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An Introduction to the Atomic Theory
Sophomore Natural ScienceThomas Aquinas College
Revised 2016
Sophomore Natural ScienceSophomore Natural Science
Revised 2007
2017
©2017
This Thomas Aquinas College Sophomore Natural Science Manual is a modified and
expanded version of the St. John’s College Freshman Laboratory Atomic Theory Manual.
We thank St. John’s College for permission to use much of their manual. The original
source for many, but not all, of the selections and editorial footnotes in the present
manual is A Source Book in Chemistry: 1400-1900, eds. H. Leicester and H. Klickstein
(Cambridge: Harvard University Press, 1952).
1
TABLE OF CONTENTS
ATOMIC THEORY MANUAL
Introduction…………………………………………………………………………………….. 3
CHAPTER I: Aristotle’s Account of Chemistry and the Elements……………………………. 5
St. Thomas Aquinas, Proemium to In Libros De Generatione et Corruptione…………… 6
St. Thomas Aquinas, De Principiis Naturae, ch. 3, on “element”………………………….. 8
St. Thomas Aquinas, De Mixtione Elementorum…………………………………………… 9
Aristotle, Selections from On Coming to Be and Passing Away,
bk. 1, chs. 1-4 and 10; bk. 2, chs. 1-3…………………….. 14
CHAPTER II: Modern Chemistry, Its New Language, and the Elements……………………… 31
The Problem of Classifying Substances…………………………………………………….. 31
An Introduction to the Phlogiston Theory…………………………………………………… 35
Lavoisier, Memoir on the Calcination of Tin and on the Cause of the Gain in Weight…….. 38
Lavoisier, Memoir on the Nature of the Principle
that Combines with Metals During Calcination…………………………… 48
Lavoisier, Memoir on Combustion in General………………………………………………. 52
Lavoisier, Elements of Chemistry, Preface…………………………………………………... 57
Morveau, Memoir on Chemical Names……………………………………………………… 65
Morveau, Lavoisier, Berthollet, Fourcroy, Method of Chemical Nomenclature……………. 66
Lavoisier, Elements of Chemistry, chs. 1-2………………………………………………….. 75
Is Heat a Substance? Two Papers to the Contrary (Davy and Rumford)……………………. 87
Lavoisier, Elements of Chemistry, ch. 8…………………………………………………….. 92
Lavoisier, Elements of Chemistry, chs. 5-7 and 16-17……………………………………… 98
On the “Acidifying Principle”……………………………………………………………….120
APPENDIX: St. Thomas Aquinas on Change of Density (optional reading)……………….122
CHAPTER III: Further Developments in the New Chemistry: Weight Laws………………….123
Berthollet, Essay on Chemical Statics………………………………………………………123
Proust, Researches on Copper………………………………………………………………128
Richter, Stoichiometry……………………………………………………………………….132
CHAPTER IV: Atoms Proposed……………………………………………………………….135
Dalton, A New System of Chemical Philosophy……………………………………………..135
Gay-Lussac, Memoir on the Combination of Gaseous Substances With Each Other……….142
APPENDIX: Dalton, “On Gay-Lussac’s Laws” (optional reading)…………………………152
CHAPTER V: Revisiting the Law of Equivalence and the Law of Multiple Proportions…..…155
Wollaston, A Synoptic Scale of Chemical Equivalents………………………………….......155
CHAPTER VI: Chemical Combination and Electricity…………………………………...……173
Davy’s Decomposition of the Alkalis and Salifiable Earths………………………………...176
Berzelius, The Electrochemical Theory……………………………………………………...178
2
CHAPTER VII: Determination of Atomic and Molecular Weights………………….………....181
Avogadro, Essay on a Manner of Determining
the Relative Masses of the Elementary Molecules…………………..……..181
Modern Chemical Symbols…………………………………….……………………………189
Dulong and Petit, Researches on Certain Important Points about the Theory of Heat……..192
Cannizzaro, Sketch of A Course of Chemical Philosophy…………………………………...196
Mendeleev: Letter to Voskresenski………………………………………………………….223
CHAPTER VIII: Structural Formulas and Valence………………………………..…………...225
Gerhardt’s System of Types…………………………………………………………………225
Couper, On A New Chemical Theory………………………………………………………..230
CHAPTER IX: The Periodic Table…………………………………………………..…….….. 249
Mendeleev, The Relation Between the Properties and Atomic Weights of the Elements……249
Mendeleev, The Periodic Law of the Chemical Elements…………………………………...253
Mendeleev’s 1879 Periodic Table…………………………………………………………...271
Notes on the Modern Periodic Table………………………………………………………...273
Philosophical Questions regarding the Atomic Theory……………………………………...276
APPENDIX: Relative Atomic Weight (1962)……………………………………………….279
AFTERWORD: “Is the Atom Really an Atom?” J. J. Thomson………………………………..281
The Modern Periodic Table……………………………………………………………………..287
3
“It is of great advantage to the student of any subject to read the original
memoirs on the subject, for the science is most completely assimilated
when it is in the nascent state.”
James Clerk Maxwell
Treatise on Electricity and Magnetism
Preface, p. xi
INTRODUCTION
The central issue in this laboratory is the atomic theory of matter. We will deal with (1)
the questions to which the theory provides some sort of answer, (2) the background from
which it developed, and (3) part of the explanatory and predictive power of the theory.
Apparently the theory cannot be logically proved starting from undeniable
premises. In what sense the theory may be considered right or true will probably only
become clear by learning a great deal about the theory as it has been developed and
modified. The belief that this is true has directed the way in which this laboratory has
been organized. Some progress should be made in understanding the interaction between
experimental work and the theory that both explains (in some sense) the experimental
results and suggests further experimental work. To emphasize this interaction the
laboratory has been arranged so that there is a general alternation between experimental
work and discussions based on original papers that deal with theory and experimental
work.
We will not examine the support for a particle theory of matter provided by the
kinetic molecular theory. To do this would require more sophistication in mathematics
and mechanics on your part than you could be legitimately expected to possess now.
However, a consistent case for atomism can be and was made without direct appeals to
the kinetic molecular theory. This is the case we will examine.
We have chosen to deal almost exclusively with the 18th and 19th century
chemistry not because we have an interest in the past history as such, but because this
seems to us the best way to learn something about the ways of this physical science. We
will ask what the ideas and experimental results are, how they are come by, and how they
fit together in a phase of science in which we have a good chance of finding answers to
some of our questions.
This laboratory will not concern itself with any 20th century developments in the
atomic theory. Our concern is with understanding the building up and justification of this
great theory as an example of scientific theory. The scientists of the 20th century
generally accepted and still accept most of the essentials of the atomic theory as we will
leave it.
You may find it helpful to think of our task as, to a large extent, unpacking the
meaning of four terms: element (Chapters I and II), compound—as distinguished from
mixture as well as from element—(Chapter III, IV, V), atom (Chapter IV), and molecule
(Chapters IV, VI, VII). Chapters VIII and IX, using the understanding of the terms now
established, further the explanation of the nature of chemical change, and make some
remarkable predictions on the basis of these explanations.
4
There is perhaps no theory of more pervasive importance in modern natural
science than the atomic theory. How one can defend this theory—one positing entities
that are not perceivable even sub-microscopically—should be of interest.
* * *
Measurement is the major link between mathematics and natural science. During
the first weeks of this semester we were primarily concerned with studying measurement
as such. In this lab we will be concerned with studying a science—chemical atomism—as
such. However, the work of this lab is related to that of the measurement segment of the
Freshman and Sophomore Natural Science in a variety of ways. Four of these are
mentioned here.
I. Many kinds of measurement previously studied will be used or referred to this
semester— length, weight, volume, density, specific gravity, center of gravity,
pressure, buoyancy, heat, temperature, specific heat, and the gas laws. Here all
the measurements will serve a single major concern.
II. In considering which characteristics of material are to be held as most important
in explaining chemical composition, which are “measurable” in the light of what
you now understand about measurement? Does this, in any way, direct which
characteristics one chooses to emphasize?
III. Consider the use made of measurement in the arguments presented. Compare, for
example, the role of measurement in the readings from Aristotle and in the
readings from Lavoisier. What significance can be attributed to the difference?
IV. During the first part of this semester you probably tacitly (or explicitly) assumed
all magnitudes were continuous, rather than composed of distinguishable parts
(recall in the Measurement Manual Question 5, p. 10, and Question 3, p. 33).
Should you reconsider this assumption in the face of a generally accepted atomic
theory of matter?
5
CHAPTER I
Aristotle’s Account of Chemistry and the Elements
READINGS:
FIRST:
Introduction to this Manual (3-4)
Aristotle, On Coming to Be and Passing Away, Book I, ch. 1, 314a1-7 (14)
St. Thomas Aquinas, Prologue to the Commentary of On Coming to Be and
Passing Away (6-7)
St. Thomas Aquinas, on the meaning of “element,” On the Principles of Nature, n.
21 (8)
SECOND:
Aristotle, On Coming to Be and Passing Away, Book I, ch. 2, 315a30-32; 315b16-
316a34; 316b17-18; 316b32-317a32 (16-19)
THIRD:
Ibid., ch. 3, 317a33-318a30; 319a3-319b5 (19-23)
Ibid., ch. 4, in toto (23-24)
FOURTH and FIFTH:
Ibid., Book I, ch. 10 (24-26)
Ibid., Book II, ch. 7, 334b4-18; 334b26-31 (27)
St. Thomas Aquinas, On the Combination of the Elements (9-13)
SIXTH:
Aristotle, On Coming to Be and Passing Away, Book II, selections from chapters 1-
3 (28-30)
6
St. Thomas Aquinas
In Libros De Generatione et Corruptione
{Commentary on the Books On Coming to Be and Passing Away}
Proemium [Translation by C. Decaen]
1. Sicut tradit Philosophus in iii De
Anima, scientiae secantur quemadmodum
et res: Nam omnes habitus distinguuntur
per obiecta, ex quibus speciem habent. Res
autem quas considerat naturalis, sunt
motus et mobile; dicit enim Philosophus in
ii Physic. quod quaecumque mota movent,
sunt physicae speculationis. Et ideo oportet
quod secundum differentiam motuum et
mobilium, distinguantur et ordinentur
partes scientiae naturalis.
Primus autem motuum est motus
localis, qui est perfectior ceteris, et
communis omnibus corporibus naturalibus,
ut probatur in viii Physic.. Et ideo post
considerationem motuum et mobilium in
communi, quae fuit tradita in libro
Physicorum, primo oportuit quod
tractaretur de corporibus secundum quod
moventur motu locali, in libro De Caelo;
quae est secunda pars scientiae naturalis.
Restat igitur consideratio de motibus
aliis consequentibus, qui non sunt
communes omnibus corporibus, sed
inveniuntur in solis inferioribus. Inter quos
principatum obtinet generatio et corruptio.
Alteratio enim ordinatur ad generationem
sicut ad finem, qui est perfectior naturaliter
his quae sunt ad finem. Augmentum etiam
consequenter se habet ad generationem:
Nam augmentum non fit sine quadam
particulari generatione, qua scilicet
nutrimentum convertitur in nutritum; sicut
Philosophus dicit in ii De Anima quod
cibus nutrit inquantum est potentia caro,
augmentat autem inquantum est potential
quanta caro. Et ideo necesse est, quia hi
motus quodammodo consequenter se
habent ad generationem, quod simul de his
1. Just as the Philosopher treats it in the third
book On the Soul, the sciences are divided in the
same way things are: For all habits are
distinguished through the objects from which they
have their species. However, the things that the
naturalist considers are motion and the mobile;
for the Philosopher says in the second book of
Physics that whatever moved things move are of
the contemplation of physics. And therefore it is
necessary that the parts of natural science be
distinguished and ordered according to the
differences of motions and mobiles.
But the first of the motions is local motion,
which is more perfect than the others, and is
common to all natural bodies, as is shown in the
eighth book of Physics. And therefore after the
universal consideration of motions and mobiles,
which has been treated in the book of Physics, it
was necessary that one treat first of bodies
according as they are moved with local motion, in
the book of On the Heavens, which is the second
part of natural science.
There remains, therefore, the consideration of
the other consequent motions, which are not
common to all bodies, but are found in the lower
bodies alone. Among which generation and
corruption {alt. coming to be and passing away}
hold the chief place. For alteration is ordered to
generation as to an end, which is naturally more
perfect than those things that are for the end.
Growth also bears itself as consequent to
generation: For growth does not come to be
without some particular generation by which,
namely, the nutriment is converted into the one
nourished, just as the Philosopher says in the
second book of On the Soul that food nourishes
inasmuch as it is potentially flesh, but it causes
growth inasmuch as it is potentially so much
flesh. And therefore it is necessary, because these
motions bear themselves in some way as
7
et de generatione et corruptione tractetur. consequent to generation, that one treat of them
and of generation and corruption together.
2. Est autem considerandum quod de
unoquoque quod in pluribus invenitur,
prius est considerandum in communi,
quam ad species descendere: Alioquin
oporteret idem dicere multoties, ita scilicet
quod in singulis id quod est commune
repeteretur, sicut probat Philosophus in i
De Partibus Animalium. Et ideo prius
oportuit de generatione et corruptione in
communi determinare, quam ad partes eius
descendere.
Similiter etiam considerare oportet
quod, si in aliquo genere aliquod primum
invenitur quod sit causa aliorum, eiusdem
considerationis est commune genus et id
quod est primum in genere illo. Quia illud
primum est causa totius generis, oportet
autem eum qui considerat genus aliquod,
causas totius generis considerare. Et inde
est quod Philosophus in metaphysica simul
determinat de ente in communi et de ente
primo, quod est a materia separatum. Sunt
autem in genere generabilium et
corruptibilium quaedam prima principia,
scilicet elementa, quae sunt causa
generationis et corruptionis et alterationis
in omnibus aliis corporibus.
Et inde est quod Aristoteles in hoc
libro, qui est tertia pars scientiae naturalis,
determinat non solum de generatione et
corruptione in communi et aliis motibus
consequentibus, sed etiam de generatione
et corruptione elementorum.
His igitur praelibatis ad demonstran-
dum intentionem Aristotelis in hoc libro,
accedendum est ad expositionem eius.
2. However, one should consider that, of each and
every thing that is found in many, one should
make a general consideration before descending
to the species. Otherwise it would be necessary to
say the same things many times, such that that
which is common in the particulars would be
repeated, as the Philosopher shows in the first
book of On the Parts of Animals. And therefore it
was necessary to determine of generation and
corruption in general before descending to its
parts.
Likewise also one must consider that if in
some genus something first is found which is the
cause of the others [in the genus], the common
genus and that which is first in that genus are of
the same consideration. But because that first one
is the cause of the whole genus, it is necessary
that he who considers some genus consider the
causes of the whole genus. And thence it is that in
metaphysics the Philosopher determines
simultaneously of being in common and of the
first being, which is separate from matter. In the
genus of things that can be generated and
corrupted, however, there are certain first
principles, namely the elements, which are the
cause of generation and corruption and alteration
in all other bodies.
And thence it is that Aristotle, in this book,
which is the third part of natural science,
determines not only generally of generation and
corruption and the other consequent motions, but
also of the generation and corruption of the
elements.
So with these things settled first for
demonstrating the intention of Aristotle in this
book, let us now approach toward expounding it.
8
St. Thomas Aquinas on the Meaning of “Element”
De Principiis Naturae, ch. 3, nn. 24-25 [Translation by C. Decaen]
24. Elementum vero non dicitur proprie nisi
de causis ex quibus est compositio rei, quae
proprie sunt materiales. Et iterum non de
qualibet causa materiali, sed de illa ex qua
est prima compositio: sicut nec membra
elementa sunt hominis, quia membra etiam
sunt composita ex aliis; sed dicimus quod
terra et aqua sunt elementa, quia haec non
componuntur ex aliis corporibus, sed ex ipsis
est prima compositio corporum naturalium.
24. “Element” can be properly said only of the
causes from which a thing is composed, which are
properly material causes. Further, it is not [said] of
just any material cause, but of that from which the
thing is first composed, just as neither are the
[bodily] members of a man elements, since the
members are also composed from other things. But
we do say that earth and water are elements, since
these are not composed from other bodies, but the
first composition of natural bodies is from them.
25. Unde Aristoteles in quinto Metaph. dicit
quod elementum est id ex quo componitur
res primo, et est in ea, et non dividitur
secundum formam. Expositio primae
particulae, ex quo componitur res primo,
patet per ea quae diximus. Secunda particula,
scilicet et est in ea, ponitur ad differentiam
illius materiae quae ex toto corrumpitur per
generationem: sicut panis est materia
sanguinis, sed non generatur sanguis nisi
corrumpatur panis; unde panis non remanet
in sanguine: unde non potest dici panis
elementum sanguinis. Sed elementa oportet
aliquo modo manere, cum non
corrumpantur, ut dicitur in libro de Gener.
Tertia particula, scilicet et non dividitur
secundum formam, ponitur ad differentiam
eorum scilicet quae habent partes diversas in
forma, idest in specie, sicut manus, cuius
partes sunt caro et ossa, quae differunt
secundum speciem. Sed elementum non
dividitur in partes diversas secundum
speciem, sicut aqua, cuius quaelibet pars est
aqua. Non enim oportet ad esse elementi ut
non dividatur secundum quantitatem, sed
sufficit si non dividatur secundum speciem:
et si etiam non dividitur, dicitur elementum,
sicut litterae dicuntur elementa dictionum.
25. Whence Aristotle, in the fifth book of the
Metaphysics, says that an element is “that from
which a thing is first composed, and is in it, and is
not divided according to form.” The explanation of
the first phrase, “from which a thing is first
composed,” is clear from what we have said. The
second phrase, namely “and is in it,” is posited for
distinguishing [an element] from that matter which
is wholly corrupted through generation, just as
bread is the matter of blood, but blood is not
generated unless the bread is corrupted; whence
bread does not remain in blood, whence bread
cannot be called an element of blood. But elements
in some manner must remain, since they are not
corrupted, as is said in the [first] book of On
Coming to Be and Passing Away. The third phrase,
namely “and is not divided according to form,” is
posited for distinguishing [elements] from those
things that have parts diverse in form, that is, in
species, such as a hand, the parts of which are flesh
and bone, which differ according to species. But an
element is not divided into parts diverse according
to species, such as water, any part of which is
water. For it is not necessary for the being of an
element that it not be divided according to quantity,
but it suffices that it not be divided according to
species. And even if it is not divided it is called an
element, just as letters are called elements of
speech.
9
St. Thomas Aquinas
De Mixtione Elementorum
{On the Combination of the Elements} [Translated by J. F. Nieto; with minor emendations.]
I
1. Dubium apud multos esse solet quomodo
elementa sint in mixto.
2. Videtur autem quibusdam quod,
qualitatibus activis et passivis elementorum
ad medium aliqualiter reductis per
alterationem, formae substantiales
elementorum manent:
3. Si enim formae substantiales non
maneant, corruptio quaedam elementorum
esse videbitur et non mixtio.
4. Rursus si forma substantialis corporis
mixti sit actus materiae non praesuppositis
formis simplicium corporum, simplicia
corpora elementorum rationem amittent.
5. Est enim elementum ex quo componitur
aliquid primo, et est in eo, et est indivisibile
secundum speciem; sublatis enim formis
substantialibus, non sic ex simplicibus
corporibus corpus mixtum componetur,
quod in eo remaneant.
1. To many, how the elements are in a combined
thing is usually uncertain.
2. However, it seems to certain men that, with
the active and passive qualities of the elements
having been by alteration reduced to a mean of
some sort, the substantial forms of the elements
remain.
3. For if the substantial forms do not remain,
there would seem to be a certain corruption of
the elements and not a combination.
4. Again, if the substantial form of the combined
body be the actuality of the matter, without the
forms of the simple bodies having been
presupposed, the simple bodies would lose the
notion of elements.
5. For an element is that from which something
is first composed, and is in it, and is indivisible
according to species; for with the substantial
forms destroyed, the combined body would not
be so composed from the simple bodies that they
would remain in it.
II
6. Est autem impossibile sic se habere.
7. Impossibile est enim materiam secundum
idem diversas formas elementorum
suscipere. Si igitur in corpore mixto formae
elementorum salventur, oportebit diversis
partibus materiae eas inesse.
8. Materiae autem diversas partes accipere
est impossibile, nisi praeintellecta quantitate
6. But it is impossible that it be this way.
7. For it is impossible that matter insofar as it is
the same take on the diverse forms of the
elements. Therefore, if the substantial forms of
the elements be preserved in the combined body,
they must be in diverse parts of matter.
8. But it is impossible to take diverse parts of
matter except with quantity previously
10
in materia; sublata enim quantitate,
substantia indivisibilis permanet, ut patet in
primo Physic., ex materia autem sub
quantitate existente, et forma substantiali
adveniente, corpus physicum constituitur.
Diversae igitur partes materiae formis
elementorum subsistentes plurium corporum
rationem suscipiunt.
9. Multa autem corpora impossibile est esse
simul. Non igitur in qualibet parte corporis
mixti erunt quatuor elementa; et sic non erit
vera mixtio, sed secundum sensum, sicut
accidit in aggregatione corporum
insensibilium propter parvitatem.
10. Amplius, omnis forma substantialis
propriam dispositionem in materia requirit,
sine qua esse non potest: Unde alteratio est
via ad generationem et corruptionem.
Impossibile est autem in idem convenire
propriam dispositionem, quae requiritur ad
formam ignis, et propriam dispositionem
quae requiritur ad formam aquae, quia
secundum huiusmodi dispositiones ignis et
aqua sunt contraria. Contraria autem
impossibile est esse in eodem. Impossibile
est igitur quod in eadem parte mixti sint
formae substantiales ignis et aquae. Si igitur
mixtum fiat remanentibus formis
substantialibus simplicium corporum,
sequitur quod non sit vera mixtio, sed solum
ad sensum, quasi iuxta se positis partibus
insensibilibus propter parvitatem.
understood to be in the matter, for with quantity
having been taken away substance remains
indivisible, as is clear in the first book of the
Physics. But a physical body is constituted from
matter existing under quantity and a substantial
form coming [to it]. Therefore the diverse parts
of matter subsisting by the forms of the elements
take on the notion of many bodies.
9. But it is impossible for many bodies to be
together. Therefore the four elements will not be
in any part of the combined body. And so there
will not be a true combination, but one according
to sense, as happens in an aggregate of bodies
insensible on account of smallness.
10. Additionally, every substantial form requires
a proper disposition in the matter, without which
it cannot be. Whence alteration is the path to
generation and corruption. But it is impossible
that in the same thing there come together the
proper disposition that is required for the form of
fire and the proper disposition that is required for
the form of water, since according to dispositions
of this sort fire and water are contraries. But it is
impossible that contraries be in the same thing.
Therefore it is impossible that in the same part of
a combined thing there be the substantial forms
of fire and water. If, therefore, there come to be a
combined thing with the substantial forms of the
simple bodies remaining, it follows that it will
not be a true combination, but one only
according to sense, as if with parts insensible on
account of smallness having been placed next to
each other.
III
11. Quidam autem utrasque rationes vitare
volentes, in maius inconveniens inciderunt.
Ut enim mixtionem ab elementorum
corruptione distinguerent, dixerunt formas
substantiales elementorum aliqualiter
remanere in mixto.
11. But some, wishing to avoid both ar- guments,
have fallen into a greater incongruity. For, in
order that they might distinguish the combination
of the elements from their corruption, they have
said that the substantial forms of the elements
remain in the combined thing in some way.
11
12. Sed rursus ne cogerentur dicere esse
mixtionem ad sensum, et non secundum
veritatem, posuerunt quod formae
elementorum non manent in mixto
secundum suum complementum, sed in
quoddam medium reducuntur; dicunt enim
quod formae elementorum suscipiunt magis
et minus et habent contrarietatem ad
invicem.
13. Sed quia hoc manifeste repugnat
communi opinioni et dictis Aristotelis
dicentis in Praedic., quod substantiae nihil
est contrarium, et quod non recipit magis et
minus; ulterius procedunt, dicentes quod
formae elementorum sunt imperfectissimae,
utpote materiae primae propinquiores: Unde
sunt mediae inter formas substantiales et
accidentales; et sic, inquantum accedunt ad
naturam formarum accidentalium, magis et
minus suscipere possunt.
12. But again, lest they be forced to say that
there is a combination according to sense and not
according to truth, they have posited that the
forms of the elements do not remain in the
combined thing according to their fullness, but
are reduced into a certain mean. For they say that
the forms of the elements take on more and less,
and have contrariety toward each other.
13. But because this is manifestly repugnant to
common opinion and to the words of Aristotle
saying, in the Categories, that nothing is
contrary to substance and that it does not receive
more and less, they proceed further, saying that
the forms of the elements are the most imperfect,
as they are closer to first matter. Whence they
are means between substantial and accidental
forms, and thus, inasmuch as they approach the
nature of accidental forms, they can take on more
and less.
IV
14. Haec autem positio multipliciter
improbabilis est.
15. Primo quidem quia esse aliquid medium
inter substantiam et accidens est omnino
impossibile:
16. Esset enim aliquid medium inter
affirmationem et negationem. Proprium enim
accidentis est in subiecto esse, substantiae
vero in subiecto non esse. Formae autem
substan-tiales sunt quidem in materia, non
autem in subiecto: Nam subiectum est hoc
aliquid; forma autem substantialis est quae
facit hoc aliquid, non autem praesupponit
ipsum.
17. Item ridiculum est dicere medium esse
inter ea quae non sunt unius generis; ut
probatur in decimo Metaph., medium enim et
extrema ex eodem genere esse oportet; nihil
14. But this position can be disproven in many
ways.
15. First, because that there be some mean
between substance and accident is altogether
impossible.
16. For there would be some mean between
affirmation and negation. For it is proper to
accident to be in a subject, but to substance not
to be in a subject. Moreover, substantial forms
are in fact in matter, but not in a subject, for a
subject is a ‘this something’, but a substantial
form is what makes a ‘this something’, and
does not presuppose it.
17. Again, to say there is a mean between
things that are not of one genus is ridiculous, as
is proved in the tenth book of the Metaphysics,
for the mean and the extremes must be from the
12
igitur medium esse potest inter substantiam et
accidens.
18. Deinde impossibile est formas
substantiales elementorum suscipere magis et
minus. Omnis enim forma suscipiens magis et
minus est divisibilis per accidens, inquantum
scilicet subiectum eam potest participare vel
magis vel minus. Secundum autem id quod
est divisibile per se vel per accidens, contingit
esse motum continuum, ut patet in VI Physic..
Est enim loci mutatio et augmentum et
decrement-tum, secundum quantitatem et
locum quae sunt per se divisibilia; alteratio
autem secundum qualitates quae suscipiunt
magis et minus, ut calidum et album. Si igitur
formae elementorum suscipiunt magis et
minus, tam generatio quam corruptio
elementorum erit motus continuus. Quod est
impossibile, nam motus continuus non est nisi
in tribus generibus, scilicet in quantitate et
qualitate, et ubi, ut probatur in V Physic.
19. Amplius, omnis differentia secundum
formam substantialem variat speciem. Quod
autem recipit magis et minus, differt quod est
magis ab eo quod est minus et quodammodo
est ei contrarium, ut magis album et minus
album. Si igitur forma ignis suscipiat magis et
minus, magis facta vel minus facta speciem
variabit, et non erit eadem forma, sed alia. Et
hinc est quod Philosophus dicit in VIII
Metaph., quod sicut in numeris variatur
species per additionem et subtractionem, ita
in substantiis.
same genus. Nothing, therefore, can be a mean
between substance and accident.
18. Further, it is impossible that the substantial
forms of the elements take on more and less.
For every form taking on more and less is
divisible accidentally, inasmuch as the subject
can share it either more or less. But continuous
motion occurs according to what is divisible
through itself or accidentally, as is clear in the
sixth book of the Physics. For change of place
and growth and decrease are according to
quantity and place, which are divisible through
themselves, but alteration [is divisible]
according to the qualities that take on more and
less, such as the hot and the white. So if the
forms of the elements take on more and less,
then both the generation and the corruption of
the elements will be a continuous motion;
which is impossible, for continuous motion is
not but in three genera, namely in quantity,
quality, and where, as is proved in the fifth
book of the Physics.
19. Further, every difference according to
substantial form varies the species. But that
which receives more and less differentiates that
which is more from that which is less, and in a
certain way is contrary to it, as the more white
and the less white. So if the form of fire were to
take on more and less, then having been made
more or having been made less will vary the
species, and it will not be the same form, but
another. And so it is that the Philosopher says
in the eighth book of the Metaphysics that, just
as in numbers the species is varied through
addition and subtraction, so also in substances.
V
20. Oportet igitur alium modum invenire,
quo et veritas mixtionis salvetur, et tamen
elementa non totaliter corrumpantur, sed
aliqualiter in mixto remaneant.
20. Therefore another manner must be found by
which both the truth of the combination might be
preserved, and yet the elements might not be
totally corrupted, but remain in the combined
thing in some way.
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21. Considerandum est igitur quod
qualitates activae et passivae elementorum
contrariae sunt ad invicem et magis et
minus recipiunt. Ex contrariis autem
qualitatibus quae recipiunt magis et minus
constitui potest media qualitas, quae sapiat
utriusque extremi naturam, sicut pallidum
inter album et nigrum, et tepidum inter
calidum et frigidum. Sic igitur, remissis
excellentiis qualitatum elementarium,
constituitur ex his quaedam qualitas media,
quae est propria qualitas corporis mixti,
differens tamen in diversis secundum
diversam mixtionis proportionem: Et haec
quidem qualitas est propria dispositio ad
formam corporis mixti, sicut qualitas
simplex ad formam corporis simplicis.
22. Sicut igitur extrema inveniuntur in
medio, quod participat naturam utriusque,
sic qualitates simplicium corporum
inveniuntur in propria qualitate corporis
mixti. Qualitas autem simplicis corporis est
quidem aliud a forma substantiali ipsius,
agit tamen in virtute formae substantialis,
alioquin calor calefaceret tantum, non
autem per eius actionem forma
substantialis educeretur in actum; cum
nihil agat ultra suam speciem. Sic igitur
virtutes formarum substantialium
simplicium corporum in corporibus mixtis
salvantur.
23. Sunt igitur formae elementorum in
corporibus mixtis non quidem actu, sed
virtute: Et hoc est quod Aristoteles dicit in
I De Gener.: “Non manent igitur,”
elementa scilicet in mixto, “actu, ut corpus
et album, nec corrumpuntur nec alterum
nec ambo: Salvatur enim virtus eorum.”
21. So one must consider that the active and
passive qualities of the elements are contrary to
each other and allow of more and less. But from
contrary qualities that allow of more and less can
be constituted a mean quality that tastes of the
nature of each extreme, just as the pallid between
the white and the black, and the tepid between the
hot and the cold. So, with the extremes of the
qualities of the elements having been so remitted,
there is constituted from these a certain mean
quality that is the proper quality of the combined
body, differing nevertheless in diverse ones
according to the diverse proportion of the
combination. And this quality is indeed the proper
disposition for the form of the combined body,
just as the simple quality is for the form of the
simple body.
22. So just as extremes are found in a mean that
shares the nature of each, so the qualities of the
simple bodies are found in the proper quality of
the combined body. The quality of the simple
body, however, is something other than its
substantial form, yet it acts in virtue [alt. power]
of the substantial form, otherwise heat would only
heat, and through its action a substantial form
would not be led forth into actuality, since nothing
acts beyond its own species. So in this way the
virtues [alt. powers] of the substantial forms of the
simple bodies are preserved in the combined
bodies.
23. So the forms of the elements are in combined
bodies not actually, but virtually [alt. by power].
And this is what Aristotle says in the first book of
On Coming to Be and Passing Away: “Therefore
they do not remain,” that is, the elements in the
combined thing, “actually, as [do] the body and
the white, and neither are they corrupted, neither
one nor both. For their virtue is preserved.”
14
Aristotle
De Generatione et Corruptione
(On Coming to be and Passing Away)
[H. Joachim translation (taken from the Basic Works of Aristotle, McKeon
edition), with emendations by C. Decaen; passages in brackets indicate implied
words or, if in italics, the Greek of the immediately preceding word(s).
Occasionally when the Greek is given, an alternate rendering is included
(indicated by the abbreviation “alt.”). Paragraph numbering follows that in the
Moerbeke translation in St. Thomas’s commentary.]
Note: the grayed text is not part of the assigned reading.
B O O K I
Chapter 1
1.-3. About coming to be and passing away [geneseōs kai phthoras], we must
distinguish the causes and the accounts of these things in general as they apply uniformly
to all the things that come to be and pass away by nature. Further, we are to study growth
and alteration, what each of them is, and whether alteration has the same nature as
coming to be, or whether there are separate things corresponding to these different
names.
4.-6. Of the ancients, some say that what is called unqualified coming to be is
alteration, while others say that alteration and coming to be are distinct. For those who
say that all is one thing, and who generate all things out of one thing, must assert that
coming to be is alteration, and that whatever comes to be in the proper sense is being
altered, but those like Empedocles, Anaxagoras, and Leucippus, who make the matter of
things more than one, [must assert] that coming to be is different than alteration.
7. And yet Anaxagoras ignored his own utterance. He says, at all events, that coming
to be and passing away are the same as being altered; yet, in common with the others, he
affirms that the elements are many.
8. Thus Empedocles holds that the bodily elements are four, while all the elements
with the movers are six in number; whereas Anaxagoras agrees with Leucippus and
Democritus that the elements are infinite.
9. Anaxagoras posits as elements the like-parted things, for example, bone, flesh,
marrow, and everything else which is such that part and whole take the same name; while
Democritus and Leucippus say that these are composed of indivisible bodies, being
infinite both in multitude and in forms, the compounds differing one from another
according to their constituents, and their position and arrangement.
10. And the views of the school of Anaxagoras seem contrary to those of the
followers of Empedocles. Empedocles says that fire, water, air, and earth are the four
elements, and are thus simple, rather than flesh, bone, and bodies which, like these, are
like-parted. But the followers of Anaxagoras regard like-parted things as simple and
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elements, whilst they affirm that earth, fire, water, and air are composite; for each of
these is (according to them) a universal seed-bed of like-parted things.
11.-12. On the one hand, then, those who construct all things out of one must say that
coming to be and passing away are alteration, for the underlying always remains the same
and one, and such a thing we say is being altered. But, on the other hand, those who make
the genera of things more than one [must] distinguish alteration from coming to be, for
coming to be and passing away result from them being together and being separated. That
is why Empedocles also speaks this way when he says, “There is no birth [physis] of
anything, but only a mixing and a divorce of what have been mixed.” Thus it is clear that
their account in these terms is in accordance with their assumption, and that they do in
fact speak this way.
13.-14. Nevertheless, it is necessary even for them to say that alteration is something
besides coming to be, though it is impossible for them to do so consistently with what
they say. That we are right in this criticism is easy to perceive. For just as while the
substance remains unchanged, we see a change in it according to magnitude, called
growth and diminution, so also it is with alteration. Nevertheless, the statements of those
who posit more principles than one make alteration impossible. For the passions
according to which we say that alteration occurs (I mean, e.g., hot and cold, white and
black, dry and moist, soft and hard, and so forth) are differences of the elements. As
Empedocles says, “The sun everywhere bright to see, and hot; the rain everywhere dark
and cold,” and he characterizes his remaining elements in a similar manner. If, therefore,
it is impossible for fire to become water, or water to become earth, neither will it be
possible for anything white to become black, or anything soft to become hard; and the
same account applies to all the other [qualities]. Yet this is what alteration was.
15. Also, it is apparent that there is always a single matter underlying the
contraries, whether in change according to place, or according to growth and diminution,
or according to alteration; further, the being of this [matter] and alteration likewise need
each other. For if there is alteration, then the underlying is one element, and all things
that admit of change into one another have one matter. And, conversely, if the underlying
is one, there is alteration. 16. Empedocles, then, seems to speak contrary both to the appearance and to
himself. For he denies that any one of his elements comes to be out of any other, insisting
that they are the things out of which everything else comes to be; and yet (having brought
the entirety of nature, except Strife, together into one) he maintains, simultaneously with
this denial, that each thing once more comes to be out of the One. Hence it was clearly
out of a one that this became water and that fire, various portions of it being separated off
by certain differences or passions, as indeed he calls the sun white and hot, and the earth
heavy and hard. If, therefore, these differences be taken away (for they can be taken
away, since they came to be), it will clearly be inevitable for earth to come to be out of
water and water out of earth, and for each of the other elements to undergo a similar
transformation—not only then, but also now—if they change their passions. And, to
judge by what he says, they can be attached to things and can again be separated from
them, especially since Strife and Love are still fighting with one another. It was owing to
this same conflict that the elements were generated from a One at the former period, for
presumably fire, earth, and water were no longer beings while they were one in the All.
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17. But it is not clear either whether we should regard his principle as one or
many—I mean fire and earth, and the other elements. For, on the one hand, there is one
element insofar as it underlies as matter, as that out of which earth and fire come to be,
changing through motion. On the other hand, insofar as the one results from composition
[ek syntheseōs] by them being together, whereas they result from coming apart, the many
are more elemental and prior by nature.
Chapter 2
18. We have therefore to inquire generally of unqualified coming to be and passing
away: whether it exists or does not exist, and how it exists, and also of the other simple
motions, like growth and alteration.
19. Thus Plato, on the one hand, looked into coming to be and passing away, but only
at how it is present in things, and the coming to be of the elements, but not of all things;
as to how flesh or bones or any of the other things of this sort [come to be] he said
nothing; nor about in what way alteration or growth are present in things. In general, no
one except Democritus has applied himself to any of these things in a more than
superficial way. Democritus, however, does seem not only to have thought about all of
them, but also to be distinguished from the outset by how he does it. For, as we were
saying, no one else said anything distinctly about growth, except such as any chance man
might have said—such as, that things grow by the accession of like to like ([saying]
nothing of how this happens)—and nothing about combining [mixeōs], and absolutely
nothing about each of the others, such as about acting or undergoing, in what way in
natural actions the one acts and the other undergoes.
20. Democritus and Leucippus, however, postulating the figures, make alteration and
coming to be from them, coming to be and passing away by their dissociation and
association, but alteration by their order and position.
21. And since they thought that the truth is in that which appears, and the appearances
are contrary and infinite, they made the figures infinite. Hence, with the changes of what
came together, the same thing seems different to different people, and it is transposed by
a small addition to the compound, and appears utterly other by the transposition of one
thing. For tragedy and comedy come to be from the same letters.
22. Since almost all men are of the opinion that coming to be is distinct from
alteration, and that, associating and dissociating, things come to be and pass away, but
that, passions changing, they are altered, we must stop to contemplate these things. For
they present both many and well-reasoned obstacles. For if, on the one hand, coming to
be is association, many impossible things happen; and yet, on the other hand, there are
other compelling arguments that are not easy to get through and overcome such that it
cannot be anything else. And if coming to be is not association, either coming to be
simply does not exist, or it is alteration, or else we must try to overcome this obstacle too,
it being a difficult one.
23. The starting-point [archē] of all these things is whether beings come to be and are
altered and grow, and undergo the contraries of these, because the first things are
indivisible magnitudes, or is there no indivisible magnitude—for this makes the greatest
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difference. And again, if the first things are indivisible magnitudes, are these bodies, as
Democritus and Leucippus maintain, or are they planes, as is asserted in the Timaeus?
24. To resolve bodies all the way to planes, as we have also remarked elsewhere, is
itself unreasonable. Hence, that there are indivisible bodies is far more reasonable. Yet
even this involves much that is unreasonable. Still, as we have said, it is possible to make
alteration and coming to be with them, if one transposes the same thing by turning and
order and by the varieties of the figures, as Democritus does—whence he denies that
color is a nature, for things become colored by turning. But [to explain alteration and
coming to be] is no longer possible for those who divide [bodies] into planes, for nothing
except solids results from putting them together; for they do not even attempt to generate
any passion from them.
25. The cause of a comparative inability to see wholly the things every one agrees
about is a lack of experience. Hence, those who are more at home among natural things
are more able to lay down principles such as to bring together a great many things; while
those whom attention to great accounts [alt., long speeches; tōn pollōn logōn] has
diverted from beings are too ready to draw conclusions from looking at only a few things.
One can also see from this how great is the difference between looking into things
naturally and logically [alt. dialectically; logikōs]. For concerning those saying there are
uncuttable [alt. atomic; atoma] magnitudes—they say that [otherwise] triangle itself will
be many—Democritus would appear to have been persuaded by accounts both
appropriate and natural. What we are saying will become clear as we proceed.
26. For a difficulty arises if one supposes that a body with magnitude is divisible
through and through, and that this division is possible. For what will there be that escapes
the division? For if it is divisible through and through, and this division is possible, then
it could be being divided through and through simultaneously, even if it is not divided
simultaneously; and there would be nothing impossible if this were to occur.
27. Hence whenever a body is by nature divisible through and through, whether by
bisection, or generally by any method whatever, nothing impossible will have resulted if
it has been so divided. For if it has been divided into innumerable parts, themselves
divided innumerable times, nothing impossible will have resulted, though perhaps
nobody in fact could so divide it. Since, therefore, the body is divisible through and
through, let it have been divided.
28. What, then, will remain? A magnitude? No, since then there will be something not
divided, whereas it was divisible through and through. But if it be admitted that neither a
body nor a magnitude will remain, and yet division is to take place, the body will either
consist of points (and its constituents will be without magnitude), or it will be absolutely
nothing. If the latter, then it might both come to be out of nothing and exist as a
composite of nothing; and thus the whole will be nothing but an appearance. Likewise, if
it consists of points, it will not be a quantity. For when the points were in contact and
there was just one thing with magnitude and they were together, they did not make the
whole any bigger; for when the body was divided into two or more parts, the whole was
not a bit smaller or bigger than it was before the division. Hence, even if all the points be
put together, they will not make any magnitude.
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29. But suppose that, as the body is being divided, something like sawdust is
produced, and that in this sense a body gets away from the magnitude, even then the same
argument applies. For in what sense is that divisible?
30. But if what came away was not a body but some separable form or passion, and if
the magnitude is points or contacts thus qualified, it is absurd that a magnitude should
consist of things that are not magnitudes.
31. Moreover, where will the points be? And are they immobile or mobile? And every
contact is always a contact of two things, as of some being besides the contact or the
division or the point. These, then, are the difficulties resulting from the supposition that
any and every body, whatever its size, is divisible through and through.
32. Further still, if, having divided a piece of wood or anything else, I put it together,
it is again equal to what it was, and is one. Clearly this is so, whatever the point at which
I cut the wood. The wood, therefore, has been divided potentially through and through.
What, then, is there in the wood besides the division? For even if we suppose there is
some passion, yet how is the wood dissolved into or come to be from such things? Or
how are such things separated?
33. Since, therefore, it is impossible for magnitudes to consist of contacts or points,
there must be indivisible bodies and magnitudes.
34. Yet, if we do postulate these, we are confronted with equally impossible
consequences, which we have examined in other works. But we must try to disentangle
these perplexities, and must therefore restate the problem from the starting-point [alt.
principle; archē].
35. On the one hand, then, it is in no way absurd that every sensible body should be
indivisible [alt. undivided] as well as divisible [alt. divided] at any and every point. For
the second predicate will attach to it in potency, but the first in actuality.
36.-37. On the other hand, it would seem to be impossible for a body to be potentially
divisible at all points simultaneously. For if it were possible, then it might actually occur,
with the result, not that the body would simultaneously be actually both indivisible and
divided, but that it would be simultaneously divided at any and every point.
Consequently, nothing will remain and the body will have passed away into the non-
bodily; and so it might come to be again either out of points or wholly out of nothing.
And how is that possible? But it is clear that a body is in fact divided into separable
magnitudes that are smaller at each division, i.e., into ones that are set apart from one
another and are separated. Hence, dividing a body part by part is not a breaking up that
could continue into infinity; nor can a body be simultaneously divided at every point (for
that is not possible), but only up to a certain limit. The necessary consequence, especially
if coming to be and passing away occur by association and dissociation, is that a body
must contain invisible uncuttable magnitudes [atoma megethē]. Such is the argument that
is believed to establish the necessity of uncuttable magnitudes.
38. We must now show that it conceals a faulty inference, and exactly where it
conceals it. For, since no point is in contact with another point, magnitudes are divisible
through and through in one sense, and yet not in another. When, however, it is admitted
that a magnitude is divisible through and through, it is thought that there is a point not
only anywhere, but also everywhere, in it; hence it follows that the magnitude must be
divided away into nothing. For there is a point everywhere within it, so that it consists
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either of contacts or points. But it is only in one sense that the magnitude is divisible
through and through, namely insofar as there is one point anywhere within it and all its
points are everywhere within it if you take them singly. But there are not more points
than one anywhere within it, for points are not consecutive; in this way it is not divisible
through and through. For if it were, then, if it were divisible at its center, it will be
divisible also at a contiguous point. But it is not so divisible; for position is not
contiguous to position, nor point to point. (This is a division or a composition.) Hence
there exist both dissociation and association, but neither into uncuttables [alt. atoms;
atoma] nor out of uncuttables—for that involves many impos-sibilities—nor such that
division takes place through and through—for this would have resulted if point had been
touching point. Rather, dissociation takes place into smaller parts, and association takes
place out of smaller parts.
39. Nevertheless, unqualified and complete coming to be is not defined by association
and dissociation, as some say; nor is a change in what is continuous the same thing as
alteration. On the contrary, this is where all the mistakes are made. For unqualified
coming to be and passing away occur, not by association and dissociation, but when a
thing changes from this thing to that thing as a whole. But they suppose that all such
change is alteration, whereas in fact there is a difference. For in that which underlies
there is both something corresponding to the account [kata ton logon] and something
corresponding to the matter [kata tēn hulēn]. Accordingly, whenever the change is in
these, it will be a coming to be or passing away, but whenever it is in the passions and
accidental, it will be an alteration.
40. However, dissociating and associating things come to pass away more readily.
For if water has first been dissociated into small drops, air comes to be out of it more
quickly, while if drops of water have first been associated, air comes to be more slowly.
This will become clearer in what follows.
41. For now, let so much be taken as determined: that coming to be cannot be
association, as some say it is.
Chapter 3
42. Having determined these things, we must first contemplate whether there is
anything that unqualifiedly comes to be and passes away, or whether nothing comes to be
in this chief sense [alt. properly speaking; kyriōs], but everything always comes to be
something and out of something—I mean, for example, coming to be healthy out of being
ill and ill out of being healthy, coming to be small out of being big and big out of being
small, and so on in every other instance.
43.-45. For if there is to be unqualified coming to be, something must come to be from
unqualified non-being, so that it would be true to say that non-being belongs to some
things. For qualified coming to be is from qualified non-being (e.g., out of non-white or
non-beautiful), but unqualified coming to be is from unqualified non-being.
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46.-47. Now “unqualified” [alt. simply; haplōs] means either the first thing with respect
to each category, or the universal and includes everything. Hence, if the former, there will
be a coming to be of a substance out of non-substance. But where there is not a substance
or a this something, clearly there is not any of the other categories either, such as of this
sort, or so much, or where [alt. quality, or quantity, or place where]. Otherwise, passions
would exist in separation from substances. If, on the other hand, it means what is not in
any sense at all, it will be a universal negation of everything, so that what comes to be
will have to come to be out of nothing.
48. Although we have rehearsed and settled these problems at greater length
elsewhere, we must mention them by way of summary here too. For in one sense things
unqualifiedly come to be out of that which unqualifiedly is not; yet in another sense they
come to be always out of what is. For that which is in potency, but not in actuality, must
necessarily pre-exist, being spoken of in both ways.
49. But even with these distinctions made, it is extraordinarily difficult to see how
there can be unqualified coming to be, whether out of what potentially is, or in some
other way. And we must recall this problem for further examination.
50.-51. For the question might be raised whether substance and a this something comes to
be at all, as opposed to the of a sort, the so much, or the where that come to be. And the
same question might be raised about passing away also. For if something comes to be, it
is clear that there will be (not actually, but potentially) a substance from which it comes
to be and into which that which passes away must necessarily change. Then will any of
the remaining [categories] be present in this actually? In other words, will that which is
only potentially a this something and a being, while without qualification it is not a this
something and a being, be of a sort, or so much, or somewhere? For if it is none of them,
but all of them potentially, the result will be that that which in this sense is not is capable
of being separated, and further, the greatest fear of the first philosophers will follow: that
coming to be will be out of nothing pre-existing. On the other hand, if being a this
something and a substance do not belong to it, but some of the other things said do, then
(as we said) there will be passions separable from substances.
52. We must therefore concentrate all our powers on the discussion of these
difficulties and on the solution of a further question: What is the cause of there always
being coming to be, both the unqualified as well as partial?
53. Now, the cause is either that whence, as we say, the motion begins, or it is the
matter. It is the latter cause that should be discussed here. For, as to the other cause, we
have already explained (in our accounts on motion) that it involves something immobile
through all time and something always being moved. And the treatment of the first of
these—of the immobile principle—belongs to another, and prior philosophy; while as
regards that which sets everything else in motion by being itself continuously moved, we
shall have to explain later which amongst the particular causes exhibits this character. But
at present we are speaking of the cause placed in the species of matter, to which it is due
that passing away and coming to be never fail to occur in nature. For perhaps, if we
succeed in clearing up this question, it will simultaneously become clear what account we
ought to give of that which perplexed us just now about unqualified passing away and
coming to be.
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54. Enough difficulty is involved in determining the cause of the continuity of coming
to be, if in fact what passes away vanishes into what is not, and what is not is nothing—
since what is not is neither something, nor of a sort, nor so much, nor somewhere. If,
then, some beings are always going away, why has not the universe [alt. the All; to pan]
been used up long ago and vanished away, assuming of course that there is a limit to that
out of which comes to be each thing that comes to be?
55.-56. For one ought not assume that it is on account of an infinite being out of which it
all comes to be, for that is impossible. For nothing is actually infinite, and things are
potentially infinite [only] by way of division; so that we should have to suppose there is
only one species of coming to be, one which never fails such that what comes to be is on
each successive occasion smaller than before. But in fact this is not what we see
occurring.
57. Accordingly, then, is not change necessarily ceaseless because the passing away
of something is the coming to be of something else, and the coming to be of something is
the passing away of something else? The cause implied in this solution would seem to be
adequate to account for coming to be and passing away as they occur in all existing
things alike.
58. Yet, if the coming to be of this is a passing away of that, and a passing away of
this but a coming to be of that, why are some things said to come to be and pass away
without qualification, but others only with a qualification? This question must be
investigated once more, for it demands some account. For we say “it is now passing
away” without qualification, and not merely “this is passing away”; and we call this
change coming to be, and that one passing away, without qualification. And this comes to
be something, but does not come to be without qualification; for we say “the student
comes to be knowledgeable,” not “comes to be” without qualification.
59. Now, we often make a distinction in things we say because some [sayings] signify
a this something but others do not. And the issue we are investigating results from this,
for it makes a difference into what the changing thing changes. Perhaps, for example, the
path leading into fire [alt. the passage to fire; hodos eis pyr] is unqualified coming to be,
but a passing away of something else, such as earth, but the coming to be of earth is
qualified (not unqualified) coming to be, through unqualified passing away, such as of
fire. Thus Parmenides speaks of the two—what is and what is not—as being fire and
earth. Whether we postulate these or other things of a similar kind makes no difference.
For we are trying to discover not what underlies these changes, but the way [ton tropon]
[the change happens]. Thus, the path leading into what without qualification is not is
unqualified passing away, while the path leading into what is without qualification is
unqualified coming to be. Hence, however they are characterized, whether as fire and
earth or as some other couple, the one of them will be a being and the other a non-being.
This is one way in which what comes to be and passes away without qualification is
distinguished from what does not.
60. Another is according to the sort of quality of the matter. For if the differences [of
the matter] signify more a this something, [it is] more substance; but if they signify
privation, more non-being. For example, hot is a predicament and a form, whereas cold is
a privation, and earth and fire differ from one another by these differences.
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61. The opinion, however, which most people are inclined to prefer is that the
distinction depends upon the difference between the sensible and the insensible. Thus,
when there is a change into sensible matter, people say there is coming to be; but when
there is a change into invisible matter, they call it passing away. For they distinguish
what is and what is not by their sensing and not sensing, just as what is knowable is and
what is unknowable is not, for sensation is a power of knowledge.
62. Hence, just as they deem themselves to live and to be in virtue of their sensing or
their power to sense, so too they deem things to be, and in this they are in a way on the
track of the truth, though what they actually say is not true.
63. Thus unqualified coming to be and passing away according to opinion turns out to
be different from what they are in truth. For wind and air are in truth more a this
something or form than is earth, but according to sensation they are less [a this something
and form], which explains why things are commonly said to pass away without
qualification when they change into wind and air, and to come to be when they change
into what is tangible, that is, into earth.
64. We have now stated the cause of unqualified coming to be, which is a passing
away of something else, and of unqualified passing away, which it is a coming to be of
something else. For this is due to a difference of the matter being either a substance or
not, or more or less such and such, or the matter out of which and into which the change
occurs being more or less sensible.
65-66. But why are some things said to come to be without qualification, and others only
qualifiedly to come to be, in cases different from the one we have been considering where
two things come to be reciprocally out of one another? For at present we have determined
merely why, when they come to be reciprocally out of one another, we do not attribute
coming to be and passing away equally to them both, although every coming to be is a
passing away of something else and every passing away is some other thing’s coming to
be. But the latter question is different: Why, although the one learning is said to come to
be knowledgeable but not to come to be without qualification, yet the one being born [alt.
the one growing; phuomenon] is said to come to be? These things are distinguished by
the categories. For some things signify a this something, others a sort, and others a so
much. Those things, then, that do not signify substance are not said to come to be without
qualification, but only to come to be with qualification. Nevertheless, in all things alike
we speak of coming to be according to one of the two columns,1 such as in substance, if
[it comes to be] fire but not if [it comes to be] earth; and in quality, if learned but not if
ignorant.
67. We have explained why some things come to be without qualification, but not
others—both in general, and also when the changing things are substances; and we have
said why the underlying is the cause, as matter, of the continuous occurrence of coming
to be: namely, because it is able to change into contraries and because, in substances, the
coming to be of one thing is always a passing away of another, and the passing away of
one thing is always coming to be of another.
68. But there is no need even to discuss why coming to be continues though things
are constantly being destroyed. For just as people speak of a passing away without
1See Metaphysics 986a22-27.
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qualification when a thing has passed into what is insensible and non-being, so also they
speak of a coming to be out of a non-being when a thing emerges from an insensible.
Whether, therefore, the underlying is or is not something, things come to be from non-
being, such that a thing comes to be out of what is not just as much as a thing passes
away into what is not. Hence it is reasonable enough that coming to be should never fail.
For coming to be is a passing away of what is not and passing away is a coming to be of
what is not.
69. But someone might be at a loss about whether that which without qualification is
not is one of the two contraries. For example, is earth (which is heavy) a non-being, but
fire (which is light) a being? Or, on the contrary, is not earth also a being, whereas the
matter of the earth and the fire is the non-being?
70. And again, is the matter of each different? Or is it not the same, since otherwise
they would not come to be reciprocally out of one another, contraries out of contraries?
For these things—fire, earth, water, and air—are characterized by the contraries. Or is
there one way in which the matter is the same and another in which it is different? For
while that which underlies, whatever being it has, is the same, nevertheless its being is
not the same. Let this much be said about these things, then.
Chapter 4
71. Next we must state what the difference is between coming to be and alteration, for
we say that these changes are distinct from one another.
72. Since, then, we must distinguish the underlying and the passion that is naturally
apt to be said of the underlying, and since change of each of these occurs, there is
alteration when the underlying, being something sensible, remains but the passions that
belong to it change, the passions being either contraries or intermediates. The body, for
example, although persisting as the same body, is now healthy and now ill; and the
bronze is now spherical and at another time angular, and yet remains the same bronze.
73. However, when the whole is changed, there being nothing sensible of it remaining
as underlying—like when the seed is entirely converted into blood, or water into air, or
air entirely into water—this is rightaway a coming to be of the one and a passing away of
the other.
74. This is especially [said to be so] if the change is from an insensible thing to
something sensible either to touch or to all the senses, as when water comes to be out of
air or passes away into it; for air is pretty well insensible.
75. If, however, in such cases, in the thing that has come to be any passion that is one
of a pair of contraries remains the same as it was in the thing that has passed away (such
as when out of air comes to be water, if both are transparent or cold), then it is not
necessary that that into which the one changes have the other as a passion.2 Otherwise the
change will be alteration, for example, if the musical man passed away and an unmusical
man came to be, and the man remains the same. Now, if being musical and unmusical
were not a passion through itself of this one, there would have been a coming to be of the
2 Grammatically, the “other” (thateron) could refer back to the “water,” or it could refer to the pair “transparent or
cold.”
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one and a passing away of the other; and hence, this is a passion of man, but there is
coming to be and passing away of the musical man and the unmusical man; now this is a
passion of what remains. Consequently such changes are alteration.
76. When the change from contrary to contrary is with respect to the how much [alt.
quantity], it is growth and diminution; when it is with respect to place, it is locomotion;
when it is with respect to passion and being such and such, it is alteration; but when
nothing remains of which the resultant is a passion, or in whatever way an accident, it is
coming to be and passing away.
77. What is matter most of all and in the chief sense is the underlying receptive of
coming to be and passing away; but in a way so is that of the other changes, since all
underlying things are receptive of contrarieties of some sort.
78. Let this way, then, be the determinations about coming to be—whether it exists or
not, and how—and about alteration.
Chapter 10
165. …Let us look into what combination3 is, and what it is to be combinable, and to
which beings does it belong, and how. And, further, does combination exist, or is this
false?
166. For, according to some, it is impossible for one thing to be combined with
another. For if things combined still exist and are unaltered, they are no more combined
now than they were before, but are in the same state; and if one has passed away, they
have not been combined, but one is and the other is not, whereas combination is of things
in the same state. And it makes no difference even if both things combined, when they
have come together, have passed away, because they cannot be things that have
combined if they are not beings at all. 167. What this account is looking for, it would seem, is a clarification of the difference
between combination and coming to be and passing away, and between what is combined
and what has come to be and passed away. For it is clear that they must differ, if they
exist. Therefore once these distinctions are clear, the difficulties should find a solution.
168. Now, we do not speak of the wood as combined with the fire, nor of its burning as
a combining either of its parts with one another or of itself with the fire. Rather, we say
the fire is coming to be, but the wood is passing away.
3 Mixis: The Greek word is broad enough to include the English derivative “mixing,” but the English word
“mixture,” especially in the context of chemistry, is used to name an aggregate of substances; thus, the meaning here
seems to be closer to “blending” and “combination.” The related word to mikton is correspondingly translated as
“the combinable,” or “the combined thing.” (Note also that St. Thomas’s Latin cognates mixtio and mixtum in the
related readings have been translated analogously.) Mixis should not to be confused with synthesis, which Aristotle
uses to name both the coming together of form and matter, and the juxtaposition of the parts of an aggregate. When
Aristotle uses the word synthesis to name the latter, we have translated it as “mixture.”
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169. Similarly, we speak neither of the food as combining with the body, nor of the
shape as combining with the wax and thus fashioning the lump. Nor can body combine
with whiteness, nor in general can the passions and dispositions combine with things; for
we see that they are preserved. Nor can whiteness and knowledge be combined either, nor
anything else which is not separable. (Indeed, this is a blemish in the theory of those who
assert that once all things were together and combined. For not everything can combine
with everything. On the contrary, both of the things combined must originally have
existed in separation; but no passion is separable.)
170. Since, however, some things that are exist in potency, and some exist in actuality,
the things combined can in a way be and not be. The thing that came to be from them is
in actuality, while each of the things that were before being combined still is in potency
[alt. in ability, in power; dynamei], and has not been destroyed utterly [apolōlota]. This
account is the way out of the previous difficulty. Moreover, it is evident that things
combined not only come together from having formerly been separate, but also are able
to be separated again. So neither do they both remain apart in actuality, as body and white
[do]; nor do they pass away (neither one nor both), for their potential [alt. ability, power;
dynamis] is preserved. Whence these difficulties can be set aside.
171. However, the problem connected with them—whether combination is something
relative to sensation—must be discussed. When things combining have been divided into
parts so small, and have been juxtaposed in such a manner that each of them is not
apparent to sensation, have they then been combined?
172. Or is it rather when each and every part of one thing being combined is beside a
part of the other? It is in that way that it is said that wheat combined with barley is such
that each grain of the one is beside a grain of the other.
173. But if every body is divisible, and if a body combined with a body is like-parted
[alt. homogeneous; homoiomeres], then each and every part of each thing combined
should be beside a part of the other. But since no body can be divided into least parts, and
mixture is not the same as combination, but different, it is clearly wrong to say that things
have been combined when the things being combined are preserved in small bits. For this
will be a mixture instead of a blending [krasis] or combination, nor will the part have the
same account as the whole. But we say that if there has been a combination, the
combined thing must be like-parted, and that, just as any part of water is water, any part
of such a blend is the same as the whole. However, if combination is merely a mixture of
small bits, none of these consequences will follow, but [the bits] will be combined merely
relative to sensation.
174. And the same thing will be combined to one man whose eyes are not sharp, and
nothing will be combined to the eye of Lynceus.
175. It is also [clearly wrong to say that they are combined] by being divided such that
each and every part of each is beside a part of the other; for it is impossible for things to
be so divided.
176. Either, then, there is no combination, or we must again say how it can come to be.
Now, there are, as we admit, some things that can act and others that can be acted upon
by these former ones. Moreover, on the one hand, for some things there is changing back
and forth—namely, those of which the matter is the same, being able both to act upon one
another and to be acted upon by one another. On the other hand, other things, though they
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can act, cannot be acted upon—namely, those things that do not have the same matter [as
their patients].
177. Of these latter ones there is no combination. (Hence, neither the art of healing nor
health itself produces health by combining with the bodies.) Of those things that can act
and be acted upon, however, those that are easily divisible, when many of them are
placed together with few, or large ones with small, then there is no combining but rather
growth of the dominant one. For the other changes into the dominant one. (Thus a drop of
wine does not combine with ten thousand gallons of water; for its form is lost, and it is
changed into the whole of the water.)
178. On the other hand, whenever the two are more or less equal in potency [alt.
ability, power; dynamesin], then each of them changes from its own nature towards the
one dominating [alt. ruling; to kratoun]; yet neither becomes the other, but something
intermediate, and common to both. Thus it is clear that only those things that have a
contrariety can be combined, for only these are capable of being acted upon by each
other.
179-180. Further, they combine more so if small bits of each of them are placed beside
one another. For [in that condition] they change one another more easily and more
quickly, whereas it takes a long time when the agent and the patient are present in bulk.
Hence, of things divisible and capable of being acted upon, those that are easily bounded
are able to be combined. For they are easily divided into small bits, since that is what it is
to be easily bounded. For instance, liquids are the bodies most capable of combination,
since, of all divisible things, the liquid is the most easily bounded (unless it be viscous,
for these produce no effect except to multiply and increase the bulk).
181. But when only one [of the things combined] is capable of being acted upon, or is
superlatively capable and the other is only slightly capable, what is combined from both
is either no greater in size or only a little. (This is what happens with tin and copper [alt.
bronze; chalkon].) For certain existing things are indistinct and ambiguous [alt. stutter
and waver; psellizetai kai epamphatoreizei] in relation to one another. For it is apparent
how they are both slightly combined and also as though one is receptive and the other is
form. This is how it happens for these [metals]. For the tin nearly vanishes, as though it
were a passion of the copper, but one existing without matter; and having been combined
[with the copper], it is no longer present, merely having colored the copper. The same
thing happens in other instances too.
182. It is clear, then, from the foregoing that combination exists, what it is, through
what it is, and what sort of thing can be combined. For some things are such that they can
be acted upon by each other, and are easily bounded and easily divisible. For it is not
necessary either that, when they are combined, such things pass away or that they are
without qualification. And neither need they be a mixture, nor merely relative to
sensation. Rather, anything is combinable which, being easily bounded, is capable of both
being acted upon and of acting; and it is combinable with another of the same sort (for
the combinable is relative to something of the same name); and combination is the union
of those things combined that have also been altered.
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For further development of Aristotle's teaching in GC I.10 we append this excerpt from GC II.7:
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[T]here is a certain difficulty in explaining how anything is to result from two
[elements] taken together—e.g. from cold and hot, or from Fire and Earth. For if
flesh consists of both and is neither of them, nor again is a mixture of them in
which they are preserved unaltered, what alternative is left except to identify the
product of the two elements with their matter? For the passing-away of either
element produces either the other or the matter.
Now since there are differences of degree in hot and cold, then although
when either is actual without qualification, the other will exist potentially; yet,
when neither exists in the full completeness of its being, but both by combining
destroy one another's excesses so that there exist instead a hot which (for a hot) is
cold and a cold which (for a cold) is hot; then there will exist neither their matter,
nor either of the contraries in actuality without qualification, but rather an
intermediate; and this intermediate, according as it is potentially more hot than
cold or vice versa, will in accordance with that proportion be potentially twice as
hot or as cold—or three times or whatever. Thus all the other bodies will be
produced from the contraries, or from the elements, in so far as these have been
combined…. [O]ut of the elements there come-to-be flesh and bones and the
like—the hot becoming cold and the cold becoming hot when they have been
brought to the mean. For at the mean is neither hot nor cold. The mean, however,
is of considerable extent and not indivisible. Similarly, it is in virtue of a mean
condition that the dry and the moist and the rest produce flesh and bone and the
remaining combinations.
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Book II
Chapter 1
183. It has been said now how in natural changes there is present combination, contact,
acting and being acted upon, and moreover, of coming to be and passing away
unqualifiedly, how and through what cause this exists. Likewise, this has been said of
alteration, both what being altered is and how it differs from the others. It remains to
contemplate the so-called elements of bodies. For coming to be and passing away of all
substances brought together by nature do not happen without sensible bodies [being
brought together].
184. But as to the matter that underlies these sensible bodies, some say it is one,
supposing it to be something like air or fire or an intermediate between these two, but still
a body and separable. Others, however, hold that it is more than one, some naming fire
and earth, others adding air to these to make three, others adding a fourth to these,
namely water, as Empedocles did. From the association and dissociation or alteration of
these comes the coming to be and passing away of things.
185. Let there be total agreement that [saying] the first things, the change of which
(whether it be association and dissociation or some other change) results in coming to be
and passing away, are principles and elements is well said. But they err who postulate,
besides the bodies we have mentioned, a single bodily and separable matter. For it is
impossible that this body exist without a sensible contrariety. For this indefinite thing
[alt. infinite; to apeiron touto] that some say is the principle must be either light or heavy,
cold or hot….
187. We do say, however, that there is a certain matter of the sensible bodies, but it is
not separable—rather, it is always with a contrariety—and it is that out of which the so-
called elements come to be. A more precise account of this has been given in other
works, but because this is the way that the first bodies are from the matter, we must
discuss them as well. We must regard as a principle and first thing the inseparable matter
underlying the contraries. For the hot is not matter for the cold, nor the cold for the hot,
but the underlying is matter for them both. Thus, as principles we have first, that which is
potentially a sensible body, and second, the contrarieties (I mean, for example, heat and
cold), and third, fire, water, and the like. For these bodies change into one another, and
they are not as Empedocles and others say, since alteration would then have been
impossible; but the contrarieties do not change.
188. Nevertheless, even so the question remains: What sorts of contrarieties, and how
many of them, are the principles of body? For all the other thinkers assume and use them
without explaining why they are these or why they are just so many.
Chapter 2
189. Since, then, we are looking for principles of sensible body, that is, of the tangible,
and that of which the sensation is touch is the tangible, it is clear that not all the
contrarieties of bodies make forms and principles, but only those in reference to touch.
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For it is in reference to a contrariety, and indeed a tangible contrariety, that they differ
[from each other]. Whence neither whiteness and blackness, nor sweetness and bitterness,
nor similarly any of the other sensible contrarieties either, makes an element.
190. It might be said that vision is prior to touch, so that its underlying is also prior, but
this is a passion of tangible body not as tangible, but in reference to something else, even
if it happens to be prior by nature.
191. Accordingly, first of the tangibles themselves let us distinguish which qualities
are the first differences and contraries. The contrarieties in reference to touch are the
following: hot-cold, dry-moist, heavy-light, hard-soft, viscous-brittle, rough-smooth,
coarse-fine.
192. Of these, heavy and light are neither capable of acting nor of being acted upon;
they are not said of bodies in virtue of being able to act upon something or being able to
be acted upon. But the elements must be able to act upon and be acted upon in turn by
each other, since they combine and change into one another.
193. On the other hand, hot and cold, and dry and moist, are said of things of which the
one pair is able to act, and the other to be acted upon. Hot is that which associates things
of the same kind (for dissociating, which some say fire does, is associating things of the
same type, since its effect is to eliminate what is foreign), while cold is that which brings
together and associates things of the same kind and things of different type alike.
194. And moist is that which is not bounded by any boundary of its own, but is easily
bounded; while dry is that which is easily bounded by its own boundary, but is bounded
with difficulty.
195. Fine and coarse, viscous and brittle, hard and soft, and the remaining differences,
come from these.
196. For the ability to fill things comes from [alt. is of] the moist because it has no
boundaries and is easily bounded and follows after that with which it is in contact, and
the fine [alt. subtle, thin, delicate; to lepton] is what is able to fill things up (for its parts
are fine, and that which has tiny parts is able to fill things up, for the whole of it touches
the whole, and that which is fine is most of all like this). Hence it is evident that the fine
comes from the moist, while the coarse [alt. bulky, thick, cumbersome; to pachy] comes
from the dry.
197. Again, the viscous comes from the moist, for the viscous, such as oil, is a moist
thing modified in a certain way. The brittle, on the other hand, comes from the dry, for
the brittle is that which is dry so completely that it has actually solidified due to lack of
moisture.
198. Further, the soft derives from the moist. For soft is that which yields by retiring
into itself, though it does not change position, as the moist does, which is why the moist
is not soft, although the soft comes from the moist. The hard, on the other hand, comes
from the dry, for the hard is that which is solidified, and the solidified is dry. . . .
199. It is clear, then, that all the other differences can be led back to the first four.
200. It is also clear that these admit of no further reduction. For the hot is not the same
as the moist or dry, nor the moist the same as the hot or cold; nor are the cold and the dry
from one another or from the hot and the moist. Hence these must be four.
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Chapter 3
201. Since the elements are four, and of the four six couples can be made, but
contraries are not naturally apt to be coupled, as it is impossible for the same thing to be
hot and cold, or moist and dry, it is therefore evident that the couplings of the elements
will be four: hot with dry, and moist with hot, and again cold with dry, and cold with
moist. And, according to the account, they are in agreement with the things appearing to
be simple bodies: fire, air, water, and earth. For fire is hot and dry, air is hot and moist
(for air is a sort of a vapor), water is cold and moist, while earth is cold and dry. Thus the
differences are reasonably distributed to the first bodies, and their number is in accord
with the account. . .
203. In fact, however, fire and air and each of the bodies we have mentioned are not
simple, but combined things. The simple bodies are indeed like these, but they are not the
same as them; that which is like fire is fiery [alt. fire-looking; pyroeides], but not fire;
that which is like air is aeriform [alt. air-looking; aeroeides]; and so on with the rest. But
fire is the superlative [alt. excess; hyperbolē] of heat, just as ice is the superlative of cold.
For freezing [alt. solidifying; pēxis] and boiling are superlatives of a sort, the one of cold
and the other of heat. Therefore if ice is a freezing of moist and cold, fire analogously
will be a boiling of dry and hot, which is why nothing comes to be either out of ice or out
of fire. . .
204. And, further, two of them are contrary to the other two, water being contrary to
fire and earth to air; for they are brought together from contrary passions.
205. Nevertheless, each of them, being four, belongs without qualification to one of
them: Earth belongs to {lit. is of} the dry more than to the cold, water to the cold more
than to the moist, air to the moist more than to the hot, and fire to the hot more than to the
dry.
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CHAPTER II
Modern Chemistry, Its New Language, and the Elements
The Problem of Classifying Substances
Introduction
At the beginning, we must define the names we shall use. This is especially
important here, since the meanings of many of our basic names have changed somewhat
since Aristotle’s time, though not altogether. This shift in meanings creates much
confusion, though a study of how and why it has occurred is very instructive indeed.
However, we cannot yet profitably examine the reasons for this shift; here it is enough to
clarify the meanings of the names. When you have become more familiar with the
rudiments of Aristotle’s doctrine of nature in your philosophy class, it will be fruitful to
examine the shift in meanings more deeply.
In Aristotle, the basic meaning of substance is clearly expressed in his
Categories: “that which is neither in a subject nor predicated of a subject”—in other
words, the individual existing thing, such as this man, or this tree, or this stone, which in
common speech are usually named “things” or “beings” (without qualification). Such
things as these are clearly distinguished from color, shape, size, and the like, which can
only exist by inhering in other things. By this definition, then, such things as men or
horses or other living things are obviously substances, and it is no paradox to speak of
angels as “incorporeal substances.”
In present usage—and especially in modern chemistry—the name substance
tends to have the same meaning, but is limited in its use. Those substances that are also
persons or living things are always called by the latter names, and the rest keep the
common name, just as the name “animal” is often restricted to the animals other than
man, though by so doing no one means to deny that man is an animal in the more general
sense.
The Greek equivalent of the name matter is ‘(hyle), which originally meant
“lumber.” Aristotle’s use of this word follows its original sense: “Matter” means “that
from which something is made or comes to be,” and thus, in general, whatever can
become something more perfect, or is potential in some way. Present day use of the
English noun material, as in “raw material,” “building material,” and “material for a
dress,” corresponds closely to the notion Aristotle is intentending when he speaks of
matter.
On the other hand, since about the beginning of the 20th
century matter has come
to mean almost exclusively “that which has mass and occupies space,” and Aristotle’s
sense of the word is now less common. But a thing occupies space because it has size—
length, breadth, and depth. Thus we may say that matter is now defined by two
characteristics: mass and size. Accordingly matter, as the term is now used, roughly
32
corresponds to what Aristotle calls natural body (or natural substance). For the natural is
what has an intrinsic tendency to move, and weight seems to be the most universal and
obvious example of such a tendency. And since mass is a certain principle of weight, that
which has mass, and is thus now called matter, is a natural body (or natural substance).]
It is obvious that there cannot be weight without size—i.e., without body. But can
there be body without weight? The answer is not obvious. You will see that when
Lavoisier speaks of “the matter of heat” (caloric) in Chapter 1 of his Elements of
Chemistry, he conceives it as made up of tiny, weightless particles. Thus, he (like many
of his contemporaries, you will find) is using an even more general and basic notion of
matter as “substance with size”—what Aristotle would simply call body.
In summary, then, it is clear that with Aristotle’s terminology one and the same
thing—a lump of clay, for example—may be called a substance, body, and matter, but
for three different reasons: It is a substance because it does not exist in a subject, a
body because it has size, and matter because it can become something else. These
may be three names for the same thing, but they are not synonyms.
Next, we must recall the meaning of property. As Porphyry defines it, a
property is “what belongs only to a given species, or to every member of that species, or
both of these, whether sometimes or always.” Thus, to be a doctor and to be two-footed
are both properties of man, but to be risible is even more a property, since it belongs only
to man, to every man, and always. This is “property” in the strictest sense, which is
correlative with its species. It is distinguished from the specific difference inasmuch as it
does not constitute the nature or the essence of the species, but follows from it; risibility
does not make man what he is, but is a consequence of what he is.
However, the specific natures of most things are not knowable to us directly, but
only through their properties, and often the properties we know are insufficient to
manifest the nature. Thus, a definition by properties, though not ideal, is often the best we
can do. When we are investigating natural things in detail, and considering the most
special species, our definitions will often be of this type—i.e., where properties are given
in place of specific differences. (Might there be exceptions to this rule?)
Although modern chemistry usually uses property the same way as does
Porphyry, in common usage property tends to be used more loosely, to stand for any
perceptible attribute. Thus, to compensate for this ambiguity, one sometimes speaks of
constant and specific properties, “constant” meaning “constant under given conditions.”
For example, water is transparent under all conditions, but its boiling point is only a
constant for a given set of conditions—212F at one atmosphere of pressure, etc.
We must now turn to those names that have a special relevance to modern
chemistry, as it investigates the elements. Since the more elementary is the more simple,
all these names concern the simplicity and the complexity that matter may have. (Note
that many of these distinctions will not begin to be clearly formulated by the authors we
will be reading until we enter the dispute between Berthollet and Proust in Chapter III.
Thus, as you read the following, try to evaluate the prima facie plausibility of these
distinctions.)
A mixture is two or more substances mixed together. To mix is to bring together
and intermingle substances such that the parts of one are contained evenly within the
33
parts of the other (or others). For example, when we pour salt on top of pepper in a jar,
we have brought them together, but we have not yet made a mixture. But when we shake
the jar, so that the grains of salt are evenly distributed among the grains of pepper, we
produce a mixture. Evidently, then, as the parts become finer and more evenly
distributed, they become more perfectly mixed.
A solution is a homogeneous mixture. Now, it is not certain that any mixture is
truly homogeneous; it may be that we cannot discern the distinct parts because of their
smallness—compare what St. Thomas calls a combination “ad sensum”—such as a
mixture of salt and pepper might appear a uniform gray when viewed from a distance.
Perhaps there is even reason to fear that the very idea of a homogeneous mixture is
incoherent. However, there are certainly mixtures that appear to be homogeneous, even
with the test of experiment; for example, salty water, which in every part is both wet and
salty.
In addition to immediate sensation, there are two basic ways of testing whether a
mixture is homogeneous. One way is to allow the mixture to stand, and see whether one
substance settles out of the other; the other way is to filter, and see whether the filter
separates particles that are perceptibly different from the mixture. This leads to another
experimental definition of a solution as “a sensibly homogeneous mixture in which the
constituents do not settle out of one another on standing, and are not separated by
filtration.”
In many solutions, it seems that one substance has dissolved the other. Then the
former is called the solvent, and the latter, the solute. For example, in salt water, water is
the solvent and salt is the solute, since the water has dissolved the salt. In other cases,
however, the distinction is not clear; for example, in a solution of alcohol and water, it is
not clear which, if either, is the solvent, and which the solute. (As a result, chemists
sometimes designate as the solvent whatever there is more of, and the solute whatever
there is less of, by volume.)
Usually the amount of solute that will dissolve in a given amount of solvent may
be increased only up to a certain limit; for example, 35.7 g of table salt is as much as will
dissolve in 100 mL of water at 0C.1 When this limit is reached, the solvent is said to be
saturated with the solute. But in other cases (e.g., grain alcohol in water) the substances
will dissolve in one another in all proportions; that is, one will never become saturated
with the other.
On the opposite extreme among mixtures, a suspension is an apparently
heterogeneous mixture in which the constituents settle out of one another or may be
separated by filtration, or even with tweezers, since we can see the distinction of the
parts. An example would be the aforementioned mixed salt and pepper, or a handful of
sand stirred into a glass of water.
Intermediate between these two mixtures is what is sometimes called a colloid, or
colloidal dispersion,2 where the mixture is apparently homogeneous, and yet the parts will
1 Note that the following conventions in designating units will be followed in this manual: g = gram, L =
liter, mL = milliliter. Note also that 1 cubic centimeter (cm3) is equal to one milliliter.
2 “Colloid” is from the Greek (kola), “glue,” and ς(-oeidos), meaning “form”: hence, as it
34
slowly settle out or may be separated by filtration. Examples include smoke, milk, and
paint.
A pure substance is one that is not mixed with other substances. For example,
when we say that water is pure, we mean that nothing other than water has been mixed
with it.
However, as mentioned above, the name substance is now often limited to
materials that are not as such living substances. For example, water is still called a
substance, but flesh or bone is not. Now, since all non-living substances are at least
visibly homogeneous, it is customary to make homogeneity part of the meaning of pure
substance.
Furthermore, since we know the natures of things only through their properties, it
is not possible to determine whether a given portion of matter is a pure substance without
a consideration of its properties. For if it is a pure substance, it will have properties of its
own, while if it is a mixture, it will have only the properties of its constituents. For
example, insofar as salt water is only wet and salty (to taste) and so forth, we might
reasonably regard it as only a mixture, though a homogeneous one. This leads to another,
more experimental definition of pure substance as “a homogeneous substance with a
constant set of specific properties.”
A composite substance, or compound, is a substance that is made up of two or
more substances. These substances have become a single, new substance, in contrast to a
mixture, where the original substances remain. Thus, it is proper to call a compound a
substance, but not to call a mixture a substance. The latter is still many substances. Water
and table salt are examples of compounds, as we shall see in our work in the laboratory.
Even when we can see that a given sample is not simple, it is often difficult to
determine whether it is a compound or a mixture, especially when it is a solution as well.
Two very simple tests are to evaporate the sample (if it is a liquid) and to dissolve it in
something else. If the sample is a compound, it should evaporate altogether or not at all,
or dissolve altogether, or not at all. (Why is this a reasonable claim?) From this we get
another, more experimental definition of a compound: “a substance whose components
are not separable by evaporation or selective dissolution—that is, by a solvent that will
dissolve one but not the other.” (Given these distinctions, would Aristotle’s example3 of a
combination—bronze, which is composed from copper and tin—be a compound or a
mixture?)
A simple substance, or element, is a substance that is not made up of any other
substances. This does not mean that it has no components of any sort, but only that it has
no components that are themselves substances, and can exist separately. (Compare this
with our earlier reading from St. Thomas on “element.”)
Examples of elements are easy to come by, but hard to be sure of. The most
obvious criterion is negative: The substance in question has never been seen to result
from combination, nor has it ever been broken down. Likely examples are gold and
sulfur.
were, glue-formed or glue-like. 3 See Manual, p. 26, 328b7-15.
35
An Introduction to the Phlogiston Theory
The phlogiston theory was primarily the work of Georg E. Stahl in the late 17th
and early
18th
centuries. He posits and describes phlogiston in the following:
…it is the corporeal fire, the essential fire material, the true basis of fire
movement in all flammable compounds. However, except in [these
inflammable] compounds, no fire at all occurs, but it dissipates and
volatilizes in invisible particles, or at least, develops and forms a finely
divided and invisible fire, namely, heat. On the other hand, it is very
important to note that this fire material, of and by itself and apart from
other things, especially air and water, is not found united and active, either
as a liquid or in an attenuated state. But if once by the movement of fire,
with the addition of free air, it is attenuated and volatilized, then by this in
all such conditions it is lost through unrecognizable subtlety and
immeasurable attenuation . . . [It is] the first, unique, basic, inflammable
principle. But since it cannot, until this hour, be found by itself, outside of
all compounds and unions with other materials, and so there are no
grounds or basis for giving a descriptive name based on properties, I have
felt that it is most fitting to name it from its general action, which it
customarily shows in all compounds. And therefore I have chosen the
Greek name phlogiston [, “flammable”]…1
Stahl did not further commit himself concerning its nature and properties except to say
that “all corporeal compounded things have more or less of this substance,” some (such
as animal and vegetable matter, coal, sulfur, and bitumen) having more, others (such as
sand and stone) less. He left it an open question whether it could ever be isolated for
study.
The phlogiston theory was successful in explaining a wide variety of phenomena:
(1) combustion or burning; (2) calcination (the “burning” of a metal or mineral); (3)
reduction (the reverse of calcination) of calces; (4) reduction (the reverse of combustion)
of burnt substances; (5) the dissolution (i.e., corrosion) of metals and/or calces in acids.
(1) Combustible substances such as sulfur and phosphorus lose phlogiston on
heating in the air. The resulting materials, sulfuric acid and phosphoric acid, are “burnt”
substances. Charcoal is considered to be almost pure phlogiston. After burning it leaves
almost no residue. Wood, coal, oils, and dry organic materials burn very well, giving off
a great deal of phlogiston, and leave very little residue because they are composed largely
of charcoal.
(2) Metals are those substances that possess a grayish luster,2 malleability and
good heat conduction properties. When most metals are heated in air they yield calces.
1 Zymotechnia fundamentalis seu Fermentationis Theoria generalis, ch. 12 (1697).
2 All well-characterized metals are some shade of gray except copper and gold, which are, respectively,
copper-colored and gold-colored.
36
Calces are not lustrous; they are usually white, though some are colored—very few are
gray; they are generally poor heat conductors; and they are friable rather than malleable.
The conversion of a metal to a calx is explained as the departure of the phlogiston from
the metal. Thus a metal is a composite substance; it is composed of a calx and phlogiston.
(3) When a calx is heated with charcoal, the phlogiston in the carbon passes into
the calx and converts it into a metal. This works best in the absence of air. (Why might
this be?)
(4) When sulfuric acid or phosphoric acid is heated with charcoal a similar
transfer of phlogiston regenerates the original sulfur or phosphorus.
(5) When some metals dissolve (i.e., corrode) in acids they produce a gas,
sometimes called “inflammable air.” This gas is considered to be almost pure phlogiston
(in spite of its very different appearance from charcoal) because of its considerable
inflammability in air. In addition to the inflammable air, the metal in the acid produces a
white grainy substance—sometimes called a “salt”—which is identical with the substance
produced when a calx is dissolved in an acid, though in the latter case no phlogiston
(inflammable gas) is produced. Of course! The calx is dephlogisticated metal so it has no
phlogiston to lose during the process of dissolving (i.e., corroding) in an acid. Heating a
calx (or sulfuric acid, etc.) with inflammable air regenerates the metal (or sulfur, etc.)
which is what one would predict from the theory. To summarize (5):
Metal (phlogisticated calx) plus acid yields inflammable gas plus a salt (calx plus acid).
Calx plus acid yields a salt.
Calx plus inflammable air yields metal.
Some observers noted that metals gained weight on being converted into calces.
The theory required that something (or at least some principle) depart from the metal in
calcination. Stahl, among others, considered this an unimportant issue in view of the
considerable explanatory power of the theory. Others were disturbed by this weight gain
and held that the theory was defective to the extent that it did not explain it. Yet others
held that phlogiston had levity (a “negative weight”), which would account for the weight
gain. As Johann J. Becher put it in 1661, phlogiston “weighs less than nothing. Naturally,
then, the ash of your metals weighs more than the metals you burned. Something minus
another thing that weighs less than nothing weighs more than that original something.”3
In support of this latter position, it was pointed out that flame consistently has an upward
tendency. Further, Henry Cavendish in 1766 weighed a sealed vessel containing common
air and then the same vessel containing inflammable air and found that the latter weighed
significantly less. (Could this phenomenon be explained in any other way than by
positing levity?) As you later read through the memoirs of Antoine Lavoisier that
criticize the phlogiston theory, consider the importance of weight in the arguments.
As we can see above, it was generally appreciated (by Stahl among others) that air
was usually needed for the departure of phlogiston from a substance (an exception is
mentioned in (3) above). This was explained by asserting that air was necessary as a
receiver for phlogiston. Also, there was a certain limit to the amount of phlogiston a
3. Natur-Kundigung der Metallen, 1661.
37
given amount of air could receive. This explained why a candle would extinguish in a
sealed vessel of air after a short time, even though only a part of the wax had been
consumed.
Joseph Priestley, in a famous series of experiments with air started in 1774, made
a remarkable discovery studying the calx of mercury (also called red calx, red precipitate,
and precipitated mercury per se—the latter two names derive from a way of preparing the
substance other than by direct calcination). This calx is unusual in that it may be reduced
without the addition of a phlogiston-rich substance such as charcoal. He found that when
this substance was heated (always in the presence of some common air) mercury metal
and a somewhat different air were produced. This air was shown by Priestley to be
“between four- and five-times as good as common air.” This superior goodness was
established by three tests: by the greater length of time candles would burn in the air; by
the greater length of time mice could live in the air; and by a test with “nitrous airs,”
which we will not examine further here.
As a result of his studies, Priestley concluded that common (atmospheric) air is
not the element it was long thought to be, but is actually elemental air that has been about
four-fifths saturated with phlogiston—in other words, it is a mixture. The air he prepared
from the mercury calx, and later from other substances as well, was thus considered pure
air or dephlogisticated air. In Priestley’s view, when red calx and atmospheric air are
heated, phlogiston passes from the air to the calx, leaving the air less phlogisticated (thus,
dephlogisticated air) and producing a phlogisticated calx, that is, a metal.
Priestley also carried out studies with animal and plant respiration. Lavoisier
wrote in 1772:
Dr. Priestley, by a paper published last year in London, has greatly widened the
field of our knowledge, and has endeavored to prove by ingenious, delicate, and
very novel experiments, that the respiration of animals has the effect of
phlogisticating the air just as happened in the calcination of metals and other
chemical processes, and that the air ceases to be respirable when it becomes
overcharged and in some way saturated with phlogiston.
This was Priestley’s explanation: When animals inhale they take in common air (which is
about four-fifths phlogisticated). This air is used for combustion in the body and air of a
greater degree of phlogistication is exhaled. He understood thus, “plants, instead of
affecting the air in the same manner with animal respiration, reverse the effects of
breathing, and tend to keep the atmosphere sweet and wholesome, when it is becoming
noxious, in consequence of animals either living and breathing or dying and putrefying in
it.” Thus plants take in, in the presence of sunlight, common air, remove some of the
phlogiston from it, and expel the air in a purer (that is, freer of phlogiston) form. Thus
plants become phlogiston-rich substances. This is consistent with the eminent
combustibility of plants, at least when dry, with only a small amount of ash (earth) left as
a residue.
Thus Priestly was able to explain in terms of the phlogiston theory the nature of
common air, and to explain the respiration of plants and animals.
38
Antoine Laurent Lavoisier
Memoir on the Calcination of Tin in Closed Vessels and on the Cause of the
Gain in Weight that this metal acquires in the operation1
It was shown in the experiments that I described in Chapters V & VI of the work that I
published at the beginning of this year under the title of Opuscules physique et chimiques,
that when lead or tin is calcined with a burning glass
[i.e., a magnifying glass] under a glass bell immersed in
water or mercury, the volume of the air is diminished
about a twentieth by the calcination, and the weight
increase of the metal is in weight nearly equal to that of
the air destroyed or absorbed.
I thought that I could conclude from these
experiments that a portion of the air itself or some
material contained in an elastic state in the air combined
with the metals during their calcination, and that this was
the cause of the increase in weight of metallic calces.
The effervescence that consistently occurs in all revivification of metallic calces,
that is, wherever a metallic substance changes from the state of a calx to that of a metal,
lends support to this theory. I think that I have proved that this effervescence is caused by
the disengagement of an elastic fluid [i.e., a gas], of a species of air that can be retained
and measured, and, as a result of the many experiments that I have carried out, that when
this fluid is separated from metals by the addition of powdered charcoal or of any other
matter containing phlogiston, it does not differ at all from the substance that has been
given the name of fixed air2, mephitic gas, mephitic acid, all of which are synonymous
expressions, and that this gas was exactly the same whether it be disengaged from
metallic calces by powdered charcoal, from vegetables by fermentation, or from saline or
earth alkalis by solution in acids.
However decisive these experiments may have appeared, they were in
contradiction with those published by Boyle in his treatise on the weight of flame and
fire. That celebrated natural philosopher tried to calcine lead and tin in glass vessels
closed hermetically. He succeeded, in part at least, and found the calx that he obtained
weighed several grains more than the metal that he had used. From this Boyle concluded
that the material of the flame and fire penetrated through the substance of the glass and
that it combined with the metals and caused them to be converted into calces and
1 [Read at the public meeting of Martinmas: November 11, 1774 at the Royal Academy of Sciences.
Throughout this manual, the footnotes in square brackets […] should be understood to be those of the
editor, and all others to be those of the original author.]
2 [An air or gas is called “fixed” to signify merely that it had been affixed to a solid, as is indicated at the
top of the next page, which refers to the “fixation of a portion of the air.”]
39
increased their weights.
Such precise experiments made by a philosopher like Boyle were well able to put
me on guard against my own opinion, however it was evidenced to my eyes, and I
proposed, in consequence, not only to repeat them as they were made by Boyle but, if
possible, to add all the circumstances that appeared to me proper to render them even
more conclusive.
This is, first, how I reasoned with myself: If the increase in weight of metals
calcined in closed vessels is due, as Boyle thought, to the addition of the matter of the
flame and fire that penetrates through the pores of the glass and combines with the metal,
it follows that if, after having introduced a known quantity of metal in a glass vessel and
having closed it hermetically and weighed it exactly, on calcining by a fire of coals, as
Boyle did, and finally reweighing the same vessel after calcination, before opening it, its
weight should be found increased by the quantity of the matter of fire that is introduced
during the calcination.
If on the contrary, I further said to myself, the increase in weight of the metallic
calx is not due to the combination of the material of the fire nor to any exterior matter,
but to the fixation of a portion of the air contained in the vessel, the vessel should not
weigh more after calcination than before; it should simply be partly evacuated and only
increase in weight at the moment when the vacuum is released.
After these reflections I supplied myself with very pure lead and tin, which I cast
into rods or cylinders at most 3 or 4 lignes3 in diameter, in order to introduce them easily
into retorts with narrow openings. In order to cast them thus into cylinders I operated as
follows: With scissors I cut out little bands of paper 6 to 8 lignes wide and I rolled these
in spirals so as to form molds or hollow cylinders. To give greater strength to these molds
I wound them many times with fine thread and finally I closed the end that was to form
the bottom of the mold by drawing a turn of the string tight. Then, my molds being thus
prepared, I poured into each of them by a funnel of cardboard the lead or tin, and when
the metal was sufficiently cooled I removed the enveloping
paper and cleaned the surface of the cylinders very carefully
by scraping them with a knife.
This initial operation done, I collected a certain
number of new white glass retorts of a convenient capacity
and perfectly clean within. In each I placed eight onces4 of lead or tin weighed with
scrupulous exactness and then by means of an enameler’s lamp drew out the ends of their
necks into a very fine capillary that I left open.
Of a large number of retorts of various capacities that I have prepared thus, more
than three-quarters have broken, either over the enameler’s lamp or during the fusion or
cooling of the metal, and I ought to note, moreover, that this kind of experiment is not
without danger and that once the vessels have been sealed hermetically one should never
operate without having the face covered with a solid mask, for example, of tin plate
equipped with very thick glasses for the eyes.
3 [A ligne is 1/12 pouce and is approximately 2.26 millimeters.]
4 [1 livre = 16 onces; 1 once = 8 gros; 1 gros = 72 grains. A Paris livre was equivalent to 30.59 grams.]
40
These difficulties in carrying out the operations are such that I have been able to
carry out well only two experiments with tin and scarcely one with lead, but aside from
the precise and certain conclusions that I have been able to draw from those which were
completely successful, some of the others have not been completely useless either for the
purpose of this memoir or for other, less immediate objectives.
Calcination of Tin in a Glass Retort of 43 Cubic Pouces Capacity
I took one of the retorts prepared as I have just described, namely, with a neck drawn
down to a capillary by means of a lamp; this retort contained, like all of the others, 8
onces of very carefully weighed tin, and having weighed it in order to find the weight of
the retort, independent of the 8 onces of tin that it contained, I obtained the following
results, namely:
Onces
Gros
Grains
Weight of the tin
8
0
0.00
Weight of the retort
5
2
2.50
Sum
13
2
2.50
The balance that served me for all of the
experiments contained in this memoir
was constructed with particular care by
Mr. Chemin, inspector of coinage; it can
weigh up to 8 to 10 livres, and I have
reason to believe that no more perfect
instrument of this sort exists. I have
already had occasion to speak of this
same balance in a memoir on the
conversion of water into earth that was
published in the memoirs of this
Academy for 1772.
Having thus determined the
weight of the retort and of the tin therein,
I held it by the neck at a suitable distance
over a fire of charcoal and thus heated it
slowly in order to prevent its shattering.
When the tin had just begun to melt, I
closed the capillary opening at the end of
the neck of the retort by means of a
blowpipe without removing the retort
from above the fire, and then I cooled the
vessel as slowly as I had heated it.
41
This precaution of driving out a portion of the air contained in the retort before
closing it hermetically is essential, since without doing so, dangerous explosions are
liable to occur, or else one is obliged to use retorts of very thick glass, which because of
their great weight render the balance less sensitive and give rise to a new source of
uncertainty and error.
When the retort was thus rid of a part of the air that it contained and sealed
hermetically, I returned it to the balance and found for its weight:
Average Weight
Onces Gros Grains Onces Gros Grains
In the pans:
No. 1. . . . . . . . . . . .
No. 2. . . . . . . . . . . .
13 1
13 1
67.00
70.50
13 1 68.75
I repeated the same
weighing 3 days
afterwards, and I had
In the pans:
No. 1. . . . . . . . . . . .
No.2. . . . . . . . . . . . .
13 1
13 1
68.00
70.00
13 1 69.00
Sum of the two averages
And for the average
which I regarded as the
effective weight
26 3 65.75
13 1 68.87
No matter how exact the balance that one may use, this manner of weighing by
changing pans and taking the average is the sole one yielding rigorously exact results.
Onces
Gros
Grains
The weight before
dispelling the air and
closing the retort
hermetically . . . . . . .
It is thereafter found
to be . . . . . . . . . . . .
The difference being
the weight of the air
dispelled by the heat
13
13
0
2
1
0
2.50
68.87
5.63
This weight being nearly equivalent to 12 cubic pouces and the capacity of the retort
being about 43 pouces, it follows that before the retort was closed hermetically, I
42
expelled by heat about two-sevenths of the total quantity of air contained in it.
These various preliminary operations being done, I proceeded to the calcination
and for this I will transcribe what is recorded in laboratory journal for February 14 of this
year, 1774.
The retort was placed on the fire at 10:45 in the morning, but the tin was not
melted completely until 10:52, so that is to say, after seven minutes. Soon the surface
lost the brilliance that it had at first and became covered with a pellicle that grew little by
little and appeared to wrinkle, while at the same time a kind of black flake was formed.
Shortly afterward I noticed that there was formed, at the bottom of the vessel beneath the
tin, a black powder heavier than the melted metal. This species of calx did not appear to
form on the surface of the metal, as happens in calcination in the open air, but on the
contrary, on the bottom underneath the metal. At the end of a half hour the quantity of the
black powder ceased to increase and the surface of the metal became clear, no longer
displaying a pellicle or black flakes, but was simply a little less brilliant than the metal
had been at the first moment of fusion.
The black powder of which I have just spoken, although heavier than the melted
metal, was in such a fine state of division that when the retort was agitated, some of it
arose and fluttered in the interior like a kind of very light soot and settled on the inside
walls of the vessel.
At the end of an hour and ten minutes, seeing that no further change was taking
place, I began to allow the vessel to cool. Although I had very carefully regulated the fire
during the course of this operation, the bottom of the retort was nevertheless a little
deformed and elongated in the form of a pear. This seemed to indicate that there had been
during the course of the operation no exterior pressure tending to force it in, or at least, if
so, that this pressure was more than counterbalanced by the 8 onces that weighed on the
bottom of the retort.
When the vessel had cooled sufficiently I had only to weigh it again without
opening it, and even before it was entirely cooled I had the following results.
Total Weight Before Opening AVERAGE WEIGHT
Onces Gros Grains On. Gro.
Gra.
In the pans:
No. 1
No. 2
13
13
1
1
66.90
70.30
13
1
68.60
The same retort closed hermetically
before the calcination weighed. . . .
Difference . . . . .
13
1
68.87
.27
The difference is so small that it may be regarded as zero; moreover, it will be seen below
that there exist other causes of uncertainty and error of which I did not then know and
which may give rise to considerable differences.
43
From this first observation one may already be certain that nothing exterior to the
retort combines with metals during their calcination. If we suppose, then, as will be
shown later, that the metal gained in weight, we must search for the cause in the interior
of the retort.
This first fact established, I then proceeded to open the flask by heating it strongly
toward the middle of its belly with a glowing coal and then wetting the heated place with
a little water. I succeeded in this way in making a crack that I conducted around with a
glowing coal and thus divided the retort into two nearly equal portions. I took pains to
carry out this operation on a large sheet of white paper in order to make certain that not
the least fragment of the retort was lost.
When the retort had been opened thus and the air in the interior of the vessel had
come to equilibrium with the atmosphere, I weighed anew the whole comprising the
retort, the lead,5 and the black powder or calx. I found:
Total Weight After the Entrance of the Air
Average Weight
Onces Gros Grains On. Gro. Gra.
In the pans:
No. 1 . . . . . . .
No. 2. . . . . . . .
13
13
2
2
6.75
4.50
13
2
5.63
This same retort, full of air before
the calcination.
13 2 2.50
Whence, the increase in weight
during the calcination.
3.13
It has just been said that while the retort remained closed hermetically, it suffered no
increase in weight as a result of the calcination, and that the increase in weight did not
take place until after the entrance of the exterior air. Whence, in this operation more air is
found in the retort after than before the calcination, and it is evident that this excess of air
causes the increase in weight. If, then, just this increase be found in the metal, it will be
proved that the excess of air that entered served to replace the portion that combined with
the metal during the calcination and increased its weight. Therefore I weighed separately
the retort, the lead,6 and the calx that I obtained and obtained the results which follow,
namely:
5 [This is apparently an error. Tin is meant.]
6 [See previous note.]
44
Weight of the Tin Average Weight
Onces
Gros
Grains
Onces
Gros
grains
In the pans
No. 1
No. 2
7
7
6
6
37.75
37.25
7
6
37.50
No. 1
No. 2
7
7
6
6
37.50
37.00
7
6
37.25
Sum of the weights
15
5
2.75
Mean or effective weight
7
6
37.37 Weight of black powder or calx of tin
1
37.75
Total of the tin and the calx
8
0
3.12
Same tin before calcination weighed
8
0
0
Increase
3.12
To make the proof I weighed the two fragments of the retort and had:
Onces
Gros
Grains
Weight of the retort
alone
5
2
2.50
Weight of the tin
7
6
37.37
Weight of the black
powder or calx of tin
1
37.75
Total weight after
the calcination
13
2
5.62
Weight before the
calcination
13
2
2.50
Increase
3.12
The quantity of air contained in the retort was 43 cubic pouces, that is to say,
about 21 grains. We forced out, as was seen above, 5 2/3 grains of air, and of this about a
45
fifth had been absorbed. The following experiment, having been made in a larger vessel,
will present a more marked increase in weight and in consequence will give more
satisfying results.
[Lavoisier here describes a similar experiment involving a retort of 250 cubic pouces capacity.
The conclusions are the same as those arrived at in the first experiment.]
I tried to repeat with lead the experiments that I have just described, but, as I said,
I succeeded well only once and then with such uncertain and extraordinary results that I
am induced to postpone its publication.
To summarize the conclusions that may be drawn from the two experiments on
the calcination of tin that I have just described, it appears to me that we cannot refuse to
conclude that:
First, only a certain quantity of tin may be calcined in a given quantity of air.
Second, this quantity of metal calcined is greater in a larger retort than a smaller
one, although we cannot yet be certain that the quantity of metal calcined is exactly
proportional to the capacity of the vessels.
Third, retorts sealed hermetically and weighed before and after the calcination of
a portion of the tin that they contain present no change in weight, proving that the
increase in weight that the metal undergoes evidently does not arise from the matter of
fire nor from any material exterior to the retort.
Fourth, in all calcinations of tin, the increase in weight of the metal is practically
exactly equal to the weight of the air absorbed; which proves that the portion of the air
that combines with the metal during the calcination is nearly equal in specific gravity to
the air of the atmosphere.
I might add that certain considerations arising from these experiments that I made
on the calcination of metals in closed vessels, considerations that would be very difficult
for me to explain to the reader without entering into too long detail, incline me to believe
that the portion of the air that combines with metals is slightly heavier than the air of the
atmosphere, and that that which remains after the calcination, on the other hand, is a little
lighter. The specific gravity of the air, according to this supposition, would be the
resultant mean between these two airs, but more direct evidence is needed on this matter,
especially since such small differences are involved, before I can speak of it with
certainty.
The reader will easily see, as I have only too well myself, that, despite all the care
and precision that I have tried to employ in these experiments, they still leave very much
to be desired. It is the fate of all those who occupy themselves with physical and
chemical researches that they perceive a new step as soon as they have already made one,
and they would never give anything to the public if they waited until they reached the end
of the path that continually unfolds before them and continues to lengthen as they
advance along it.
I know, for instance, that it would be important in order to complete this work to
carry out a series of calcinations of metals in a great number of vessels of different
capacities in order to determine with some precision the law that governs the increase in
weight of a metal in relation to the volume of the air in which it is calcined. It would be
46
no less interesting to try calcinations in very small vessels and even in the vacuum of the
pneumatic pump, but experiments of this kind demand so much time and attention for
their proper pursuit, they are so tiresome and require so much apparatus that is
cumbersome and difficult to make, that I had not the courage to carry this work further.
This was not true of a new route that these experiments have opened to me. It has
just been seen that a portion of the air is susceptible to combination with metallic
substances to form calces, while another portion of this same air always refuses to
combine thus. This calcination has made me suspect that the air of the atmosphere is not
a simple substance at all but is composed of very different substances, and the work that I
have undertaken on the calcination and the revivification of the calx of mercury has
singularly confirmed me in this opinion. Without anticipating the conclusions that result
from this work, I think that I may announce here that all the air of the atmosphere is not
in a respirable state; that it is the salubrious portion that combines with metals during
their calcination; and that that which remains after the calcination is a kind of noxious
gas, incapable of maintaining either the respiration of animals or the combustion of
bodies. Not only does the air of the atmosphere appear to me to be apparently composed
of two elastic fluids of very different nature, but I suspect, further, that the noxious and
mephitic part is itself very compound.7
* * * * *
7 [During this period the publication of the Memoires de l’ Academie royale des sciences was several years
in arrears, and the papers, especially in Lavoisier’s case, were often drastically revised before publication.
Thus this memoir, read in 1774, was not published until the Memoires for 1774 appeared in 1777. In the
meanwhile Lavoisier had learned of Priestley’s discovery of “pure” or “dephlogisticated air” (see pp. 56-
57) and had conducted similar experiments on his own, and had revised his paper accordingly. This may
explain why here Lavoisier says that the principle that combines with metal in calcination is the salubrious
air, whereas at the beginning of this essay he had said that it is the mephitic fixed air.]
47
Questions and Problems
1. How does Boyle’s theory differ from Stahl’s phlogiston theory?
2. Why does Lavoisier (on p. 41) interchange pans?
3. On p. 42 he states that the 0.27 grains “may be regarded as zero.” How might this
statement be justified? At first glance it seems he is distorting his data to support a
preconceived result.
4. How might a phlogistonist counter Lavoisier’s claim on p. 43 that “the excess of air that
entered served to replace the portion that combined with the metal during the calcination
and increased its weight”?
5. What is Lavoisier’s criterion for something being a member of “the general class of
metallic calces”?
6. Can you justify Lavoisier’s stress on weight in his arguments? If one held to levity or if
one held that weight was not to be considered a significant factor in changes of this kind,
could you convince him that Lavoisier’s position was superior to that of a phlogistonist?
48
Lavoisier
Memoir on the Nature of the Principle that Combines with Metals
During Their Calcination and that Increases Their Weight1, 2
Are there different species of air? Is it sufficient that a body be in a durable state of
expansibility (état d’expansibilité3 durable) in order to be a species of air? Finally, are the
different airs that occur in nature or that we may produce separate substances or merely
modifications of the air of the atmosphere? Such are the principal questions that
encompass the plan I have formed and whose successive development I propose to bring
before the eyes of the Academy. But the time devoted to our public meetings does not
permit me to treat any of these questions extensively, and I will confine myself today to a
particular case and limit myself to showing that the principle that combines with metals
during their calcination, which increases their weight and constitutes them in the state of
a calx, is nothing other than the most salubrious and purest portion of the air and such
that, if the air, after having engaged in a metallic combination, becomes free again, it
appears in an eminently respirable state more capable than the air of the atmosphere of
sustaining ignition and combustion.
The majority of the metallic calces are not to be reduced, that is, returned to the
metallic state, without the immediate contact of a carbonaceous material or any substance
whatsoever containing what we call phlogiston. The charcoal that is used is completely
destroyed in this operation if it be present in suitable proportion; whence it follows that
the air that is evolved in metallic reductions with carbon is not a simple substance but in
some manner is the result of the combination of the elastic fluid disengaged from the
metal and that disengaged from the carbon. Therefore the fact that this fluid is obtained as
fixed air gives us no right to conclude that it existed in this form in the metallic calx
before its combination with the carbon.
These considerations showed me that in order to clear up the mystery of the
reduction of metallic calces it would be necessary to experiment with those calces that are
1 [This is part of one of the most famous of all Lavoisier’s memoirs. Here we have the result of the stimulus
of Priestley’s communication to Lavoisier of his discovery of “dephlogisticated air” (October 1774).
Lavoisier read it at the Rentrée Publique of the Academy on April 27, 1775. It was first revised and read
again on August 8, 1778. The following selection is taken from this later paper, which was finally printed
in the Mémoires de l’Académie royale des sciences, 1775: 520-526, published in 1778.]
2 The first experiments relative to this memoir were made more than a year ago; those on precipitated
mercury per se were first tried with a burning glass in the month of November, 1774, and made afterwards
with all necessary precaution and care conjointly with Mr. Trudaine in the laboratory at Montigny February
28 and March 1 and 2 of this year. Finally they have been repeated anew in the presence of the Duke of
Rochefoucault, Messrs. Trudaine, de Montigny, Macquer, and Cadet.
3. The word expansibilité, which I will use in this memoir, has today a definite meaning for physicists and
chemists since a modern author has defined it in a very extensive article embodying the widest and newest
viewpoints. (See Encyclopédie, vol. VI, p. 274).
49
reducible without the addition of anything. The calx of iron offered me this property and
actually, of all those calces, either natural or artificial, which we have exposed at the foci
of the large burning glasses either of the Regent or of Mr. Trudaine, there have been none
that have not been completely reduced without addition.
I tried, consequently, to reduce by means of a burning glass several species of the
calx of iron under large glass bells inverted in mercury, and I succeeded in disengaging
by this means a large quantity of elastic fluid. But at the same time this elastic fluid
became mixed with the common air contained in the bell, and this circumstance threw
much uncertainty on my results, so that none of the tests that I conducted upon this air
were perfectly conclusive and it was impossible for me to be certain whether the
phenomena I obtained arose from the common air, from that disengaged from the calx of
iron, or from the combination of the two. The experiments having failed of fully filling
my purpose, I omit their details here; they will, however, find their natural place in other
memoirs.
As much of these difficulties arise from the nature of the thing itself, from the
refractory nature of its calces, and from the difficulty of reducing them without addition, I
regarded them as insurmountable and therefore thought that I ought to direct my attention
to another species of calx, more easily treatable and being, like the calces of iron,
reducible without addition. Precipitated mercury per se, which is nothing else than a calx
of mercury, as several authors have already advanced and as will appear even more
convincingly by the reading of this memoir, precipitated mercury per se, as I said,
appeared to me to be completely appropriate for the object that I had in view, for
everyone knows today that this substance is reducible without addition at a very medium
degree of heat. Although I have repeated a great many times the experiments that I am
about to describe, I have not thought it appropriate to give the details of the each of them
here for the fear of extending the memoir too far, and consequently I have combined into
a single account the circumstances pertaining to many repetitions of the same experiment.
First, to assure myself
that the precipitated mercury
per se was a genuine metallic
calx, that it gave the same
results, the same species of air
on reduction according to the
ordinary method (that is, to
use the customary expression,
with the addition of
phlogiston), I mixed an once
of this calx with 48 grains of
powdered charcoal and
introduced the mixture into a
little glass retort of 2 cubic
pouces or more capacity. This I placed in a reverberatory furnace of proportionate size.
The neck of this retort was about a pied4 and 3 to 4 lignes in diameter and was bent in
4. [12 pouces = 1 pied.]
50
various places by means of an enameler’s lamp in such a manner that its end was
disposed beneath an ample glass bell filled with water and inverted in a tub of the same.
The apparatus that is here before the eyes of the Academy will suffice to illustrate its
operation. This apparatus, simple as it is, is even more accurate in that it has neither joints
nor lute nor any passage through which the air may enter or escape.
As soon as a fire was placed beneath the retort and the first effects of the heat felt,
the common air that it contained expanded and some little of it passed into the bell.
However, in view of the small volume of the empty part of the retort, this air made no
sensible error, and its quantity taken at the most can scarcely amount to a cubic pouce. As
the retort is heated further the air is evolved with much speed and rises through the water
in the bell. The operation did not last for more than three-quarters of an hour, the fire
being kept up during this interval. When all the calx of mercury had been reduced and the
air ceased to come forth, I marked the height of the water in the bell and found that the
quantity of air evolved had been 64 cubic pouces without counting that which was
unavoidably absorbed in traversing the water.
I submitted this air to a large number of tests, the details of which I omit, and
found that 1) it can, by shaking, combine with water and give to the water all the
properties of acidulated, gaseous, or aerated waters such as those of Seltz, Pougues,
Bussang, Pirmont, etc.; 2) it kills in some seconds animals that were placed in it; 3)
candles and all combustible bodies in general are extinguished in an instant; 4) it
precipitates lime water; 5) it combines with great ease with either fixed or volatile
alkalis,5 depriving them of their causticity and making them capable of crystallizing. All
these properties are precisely those of that species of air known under the name of fixed
air that I obtained by the reduction of minium by powdered charcoal, which calcareous
earths and effervescent alkalis evolve in combining with acids, and which vegetable
materials evolve in fermenting. It was thus established that precipitated mercury per se
gives the same products as other metallic calces when reduced with the addition of
phlogiston, and that it belongs, therefore, in the general class of metallic calces.
It then only remained to examine this calx alone, to reduce it without adding
anything, to see if some elastic fluid were evolved from it, and, supposing there were, to
determine its nature. To this end I placed in a retort of 2 cubic pouces capacity 1 once of
precipitated mercury per se alone, arranged the apparatus in the same manner as in the
preceding experiment, and operated so that all the circumstances would be exactly the
same. The reduction took place this time with a little more difficulty than when the
charcoal was added; more heat was required, and there was no sensible change until the
retort began to become slightly red. Then the air was evolved little by little, passed into
the bell, and, holding the same degree of fire during two and one-half hours, all the
mercury was reduced.
The operation completed, there was found, on the one hand, partly in the neck of
the retort and partly in a glass vessel that I placed beneath the water under the exit of the
retort, 7 gros and 18 grains of fluid mercury, and on the other hand, the quantity of air
that had passed into the bell was found to be 78 pouces; whence it follows that by
5 [“Alkalis” are soluble salts obtained from the ashes of plants.]
51
supposing that the whole loss of weight should be attributed to the air, each cubic pouce
should weigh a little less than two-thirds of a grain—a value not far removed from that of
common air.
After having thus fixed the first results, I had only to submit the 78 cubic pouces
of air that I had obtained to all the tests necessary to determine its nature, and I found
with much surprise:
1. That it would not combine with water on shaking;
2. That it did not precipitate limewater but only gave it a nearly imperceptible turbidity;
3. That it failed to unite at all with fixed or volatile alkalis;
4. That it failed entirely to diminish the causticity of these;
5. That it could be used again to calcine metals;
6. Finally, that it had none of the properties of fixed air.
In contrast to the latter, animals did not perish in it and it seemed more suitable to their
respiration. Candles and inflamed materials were not only not extinguished, but the flame
widened in a very remarkable manner and shed much more light and brilliancy than in
common air. Charcoal burned therein with a brilliance nearly like that of phosphorus, and
all combustible materials in general were consumed with astonishing rapidity. All these
circumstances have fully convinced me that this air, far from being fixed air, is in a more
respirable, more combustible state and in consequence is more pure even than the air that
sustains us.
It appears to be proved from the above that the principle that combines with and
increases the weight of metals when they are calcined is nothing other than the purest
portion of the air itself that surrounds us and that we breathe—this it is which in
calcination passes from the expansible state to the solid one. If, then, this principle is
obtained in the form of fixed air in all metallic reductions where carbon is used, it follows
that this is due to the combination of this latter with the pure portion of the air, and it is
very probable that all metallic calces would, like mercury, give only eminently respirable
air if we could reduce them all as we do precipitated mercury per se.
Since charcoal disappears completely in the revivification of the calx of mercury,
and since one retrieves in this operation only mercury and fixed air, one is forced to
conclude that the principle to which has been given till now the name fixed air is the
result of the combination of the eminently respirable portion of the air with the charcoal. I
propose to develop this in a more satisfying manner in a series of memoirs that I shall
give on the topic.
* * * * *
52
Lavoisier
Memoir on Combustion in General1
As dangerous as is the desire to systematize in the physical sciences, it is, nevertheless, to
be feared that in storing without order a great multiplicity of experiments we obscure the
science rather than clarify it, render it difficult of access to those desirous of entering
upon it, and, finally, obtain at the price of long and tiresome work only disorder and
confusion. Facts, observations, experiments—these are the materials of a great edifice,
but in assembling them we must combine them into classes, distinguish which belongs to
which order and to which part of the whole each pertains.
Systems in physical science, considered from this point of view, are no more than
appropriate instruments to aid the weakness of our organs; they are, properly speaking,
approximate methods that put us on the path to the solution of the problem; these are the
hypotheses which, successfully modified, corrected, and changed in proportion as they
are found false, should lead us infallibly one day, by a process of exclusion, to the
knowledge of the true laws of nature.
Encouraged by these reflections, I venture to propose to the Academy today a new
theory of combustion, or rather, to speak with the reserve that I customarily impose upon
myself, a hypothesis by the aid of which we may explain in a very satisfactory manner all
the phenomena of combustion and of calcination, and in part even the phenomena that
accompany the respiration of animals. I have already laid out the initial foundations of
this hypothesis on pages 279 and 280 of the first volume of my Opuscules physiques et
chimiques, but I acknowledge that, having little confidence in my own ability, I did not
then dare to put forward an opinion that might appear peculiar and was directly contrary
to the theory of Stahl and to those of many celebrated men who have followed him.
While some of the reasons that held me back perhaps remain today, facts that
appear to me to be favorable to my ideas have increased in number since and have
strengthened me in my opinion. These facts, without perhaps being too strong, have made
me more confident, and I believe that the proof or at least the probability is sufficient so
that even those who are not of my opinion will not be able to blame me for having
written.
We observe in the combustion of bodies generally four recurring phenomena that
would appear to be invariable laws of nature; while these phenomena are implied in other
memoirs that I have presented, I must recall them here in a few words.
First Phenomena: In all combustions the matter of fire or light is evolved.
Second Phenomena: Materials may not burn except in a very few kinds of air, or
rather, combustion may take place in only a single variety of air: that which Mr. Priestley
has named dephlogisticated air and which I name here pure air. Not only do these bodies
1 [Read on September 5
th, 1775. Printed in 1780 in the Mémoires de l’Académie royale des sciences, 1777:
592-600.]
53
that we call combustible not burn in either vacuum or in any other species of air, but on
the contrary, they are extinguished just as rapidly as if they had been plunged into water
or any other liquid.
Third Phenomena: In all combustion, pure air in which the combustion takes
place is destroyed or decomposed and the burning body increases in weight exactly in
proportion to the quantity of air destroyed or decomposed.
Fourth Phenomena: In all combustion the body that is burned changes into an acid
by the addition of the substance that increases its weight. Thus, for example, if sulfur is
burned under a bell, the product of the combustion is vitriolic acid; if phosphorous is
burned, the product of the combustion is phosphoric acid; if a carbonaceous substance is
burned, the product of the combustion is fixed air, formerly called acid of chalk, etc.2
The calcination of metals follows precisely the same laws, and it is with very
good reason that Mr. Macquer considers the process as a slow combustion. Thus (1) in all
metallic calcinations the matter of fire is evolved; (2) genuine calcination may take place
only in pure air; (3) air combines with the calcined body, but with this difference, that
instead of forming an acid with it, a particular combination results that is known by the
name of metallic calx.
This is not the place to show the analogy that exists between the respiration of
animals, combustion, and calcination. I will return to it in the sequel to this memoir.
These different phenomena of the calcination of metals and of combustion are
explained in a very nice manner by the hypothesis of Stahl, but it is necessary to suppose
with Stahl that the material of fire, of phlogiston, is fixed in metals, in sulfur, and in all
bodies that are regarded as combustible. Now if we demand of the partisans of the
doctrine of Stahl that they prove the existence of the matter of fire in combustible bodies,
they necessarily fall into a vicious circle and are obliged to reply that combustible bodies
contain the matter of fire because they burn and that they burn because they contain the
matter of fire. Now it is easy to see that in the last analysis this is explaining combustion
by combustion.
The existence of the matter of fire, of phlogiston in metals, sulfur, etc., is then
actually nothing but a hypothesis, a supposition that, once admitted, explains, it is true,
some of the phenomena of calcination and combustion; but if I am able to show that these
phenomena may be explained in just as natural a manner by an opposing hypothesis, that
is to say without supposing that the matter of fire or phlogiston exists in combustible
materials, the system of Stahl will be found to be shaken to its foundations.
Undoubtedly it will not be amiss to ask first what is meant by the matter of fire. I
reply with Franklin, Boerhaave, and some of the philosophers of antiquity that the matter
of fire or of light is a very subtle, very elastic fluid that surrounds all parts of the planet
that we inhabit, that penetrates bodies composed of it with greater or less ease, and that
tends when free to be in equilibrium in everything.
I will add, borrowing the language of chemistry, that this fluid is the dissolvent of
a large number of bodies; that it combines with them in the same manner as water
combines with salt and as acids combine with metals; and that the bodies thus combined
and dissolved by the igneous fluid lose in part the properties that they had before the
2 I will observe here in passing that the number of acids is infinitely greater than we think.
54
combination and acquire new ones that make them more like the matter of fire.
Thus, as I showed in a memoir deposited with the secretary of this Academy, all
aeriform liquids, all species of air are the result of the combination of any substance
whatsoever, solid or liquid, with the matter of fire or light. It is to this combination that
the aeriform liquids owe their elasticity, their specific lightness, their rarity, and all other
properties that make them like the igneous fluid.
Pure air, according to this, that which Mr. Priestley calls dephlogisticated air, is
an igneous combination in which the matter of fire or of light enters as a dissolvent and in
which another substance enters as a base. Now if in any dissolution whatsoever we
present to the base a substance with which it has more affinity, it unites instantly and the
dissolvent that it has left becomes free; it regains all its properties and escapes with the
characteristics by which it is known, that is to say, with flame, heat, and light.
To clarify whatever may be obscure about this theory let us apply it to several
examples. When a metal is calcined in pure air the base of the air, which has less affinity
with its dissolvent than with the metal, unites with the latter as soon as it is melted and
converts it into a metallic calx. This combination of the base of the air with the metal is
shown, (1) by the increase in weight that the latter undergoes during calcination, (2) by
the nearly complete destruction of the air beneath the bell. But if the base of the air were
dissolved by the matter of fire, then in proportion as this base combines with the metal
the matter of fire should become free and should produce, in evolving, flame and light. It
is concluded that the more rapid the calcination of the metal, that is to say, the more of
the base of the air is fixed in a given time, the more matter of fire will be freed at the
same time and consequently the more noticeable will be the combustion.
These phenomena, which are extremely slow and difficult to perceive during the
calcination of metals, are almost instantaneous in the combustion of sulfur and
phosphorous. I have shown by experiments, against which it appears to me rather
difficult to make any reasonable objection, that in these two combustions air, or rather the
base of air, was absorbed; that it combined with the sulfur and with the phosphorous to
form vitriolic and phosphoric acids. However, the base of the air may not pass into a new
combination without leaving its dissolvent free, and this dissolvent, which is the matter of
fire itself, should evolve with light and flame.
Carbon and all carbonaceous materials have the same effect on the base of the air:
They appropriate it for themselves and form with it by combustion an acid sui generis
known under the name of fixed air or acid of chalk. The solvent of the base of the air, the
material of the fire, is then evolved in this operation, but in less quantity than in the
combustion of sulfur and phosphorous because a portion of it combines with the mephitic
acid [i.e., fixed air] to render it into the vaporous and elastic state in which we find it.
I will observe here, in passing, that the combustion of charcoal under a bell
inverted in mercury does not occasion a very great diminution in the volume of the air
even when pure air is used in the experiment, for the reason that the mephitic acid that is
formed remains in an aeriform state, in contrast to vitriolic acid and phosphoric acids,
which condense into a concrete form as they are produced.
I might apply the same theory successfully to all combustions, but as I shall have
frequent occasion to return to this subject, I will let these general examples suffice for the
moment. Thus, to continue, the air is composed, according to me, of the matter of fire as
55
dissolvent combined with a substance that serves it as a base and in some manner
neutralizes it. Whenever a substance toward which it has more affinity is presented to this
base, it quits its dissolvent, and then the matter of fire regains its properties and reappears
before our eyes with heat, flame, and light.
Pure air, the dephlogisticated air of Mr. Priestley, is then, from this point of view,
the true combustible body and perhaps the only one in nature, and we see that there is no
longer need, in explaining the phenomena of combustion, in supposing that there exists
an immense quantity of fixed fire in all bodies that we call combustible, that on the
contrary it is very probable that little of this fire exists in metals, sulfur, and phosphorous
and in the majority of very solid, heavy, and compact bodies; perhaps even that only the
matter of free fire exists in these substances by virtue of the property that this matter has
of coming into [thermal] equilibrium with neighboring bodies.
Another striking reflection that supports the foregoing is that nearly all bodies
may exist in three different states, namely, in the solid, the liquid, which is to say, melted
state, or the state of air and vapor. These three states depend only on the greater or lesser
quantity of the matter of fire with which these bodies are penetrated and with which they
are combined. Fluidity, vaporization, and elasticity characterize the presence of fire in
great abundance; solidity, compactness, on the contrary, evidence its absence. As much,
then, as it is proved that aeriform substances and the air itself contain a large quantity of
fire, so much is it probable that solid bodies contain little.
I would be overstepping the limits that I have prescribed and that the circumstances
demand were I to undertake to show how this theory throws light on all the great
phenomena of nature. However, I cannot omit remarking upon the ease with which it
explains why the air is an elastic and rare fluid. Indeed, fire being the most subtle, elastic,
and rare of all fluids, it should communicate a part of its properties to the substance with
which it unites, and, as solutions of salts always partake of some of the properties of
water, so dissolutions by fire should retain some igneous properties.
It will be seen, then, why we cannot have combustion either in a vacuum or in any
aeriform combination where the matter of fire has a very great affinity with the base with
which it is combined.
We are no longer obliged, following these principles, to admit the presence of a
large quantity of the matter of fixed and combined fire even in the diamond itself and in a
great number of substances that have no quality like that of the matter of fire or that
possess properties incompatible with it. Finally, we are not at all obliged to maintain, as
did Stahl, that bodies that increase in weight lose a part of their substance.
I remarked above that the theory proposed in this memoir could be applied to the
explanation of a part of the phenomena of respiration, and with this I will finish.
I showed in the memoir that I read at the public meeting of last Easter that pure
air, after having entered into the lungs, leaves in part as fixed air, or the acid of chalk.
Pure air, in passing through the lungs, undergoes then a decomposition analogous to that
which takes place in the combustion of charcoal. Now in the combustion of charcoal the
matter of fire is evolved, whence the matter of fire should likewise be evolved in the
lungs in the interval between inhalation and exhalation, and it is this matter of fire
without doubt which, distributed with the blood throughout the animal economy,
maintains a constant heat of about 32 ½ degrees Réamur. This idea will appear to be
56
hazarded at first glance, but before it be rejected or condemned I beg you to consider that
it is founded on two certain and incontestable facts, namely, on the decomposition of the
air in the lungs and on the evolution of the matter of fire that accompanies all
decompositions of pure air, that is to say, all changes of pure air to the state of fixed air.
But that which further confirms that the heat of animals stems from the decomposition of
the air in the lungs is that only those animals in nature that respire habitually are warm-
blooded, and that their warmth is the greater as respiration is more frequent; that is to say,
that there is a constant relation between the warmth of an animal and the quantity of air
entering, or at least converted into fixed air in, its lungs.
Furthermore, I repeat, in attacking here Stahl’s doctrine my object is not to
substitute a rigorously demonstrated theory but solely a hypothesis that appears to me
more probable, more conformable to the laws of nature, and that appears to me to contain
fewer forced explanations and fewer contradictions.
Circumstances have permitted me to give here but a general outline of the system
and a glance at its consequences, but I propose to take up successively each point, to
develop each in different memoirs, and I venture to assert in advance that the hypothesis
that I propose explains in a very satisfactory and very simple manner the principal
phenomena of physics and chemistry.
[It was not until 1783 that Lavoisier attacked the phlogiston theory in force in a memoir entitled
“Reflections on Phlogiston, Serving to Develop the Theory of Combustion and Calcination,”
Mémoires de l’Académie royale des sciences, 1783: 505-538 published in 1786. He describes it as
a sequel to his paper published in 1777, cited above. It is a notable document, asserting that the
phlogiston theory was not only unnecessary but was incorrect, for it was in conflict with all the
facts. The conclusion of this paper follows.]
My only object in this memoir has been to give the new development of the
theory of combustion that I published in 1777 and to show that the phlogiston of Stahl is
an imaginary thing whose existence has been gratuitously supposed in metals, sulfur,
phosphorous, and all combustible bodies; that all the phenomena of combustion and
calcination may be explained in a far simpler and easier manner without phlogiston than
with it. I do not expect that my ideas will be adopted all at once; human nature bends
toward one viewpoint, and those who have envisaged nature from a certain point of view
during a part of their career change only with difficulty to new ideas: It is for time, then,
to confirm or destroy the opinions that I have presented. In the meanwhile I see with
great satisfaction that the young people who are commencing to study without prejudice,
the geometers and the natural philosophers who bring fresh minds to bear on chemical
truths, believe no longer in a phlogiston in the sense that Stahl presented it and regard all
the doctrine as a scaffolding more encumbering than useful for continuing the edifice of
chemical science.
* * * * *
57
Lavoisier
Elements of Chemistry1
Preface of the Author
When I began the following Work, my only object was to extend and explain more fully
the Memoir which I read at the public meeting of the Academy of Sciences in the month
of April 1787, on the necessity of reforming and completing the Nomenclature of
Chemistry. While engaged in this employment, I perceived, better than I had ever done
before, the justice of the following maxims of the Abbé de Condillac, in his System of
Logic, and some other of his works.
“We think only through the medium of words.—Languages are true analytical
methods.—Algebra, which is adapted to its purpose in every species of expression, in the
most simple, most exact, and best manner possible, is at the same time a language and an
analytical method.—The art of reasoning is nothing more than a language well arranged.”
Thus, while I thought myself employed only in forming a Nomenclature, and
while I proposed to myself nothing more than to improve the chemical language, my
work transformed itself by degrees, without my being able to prevent it, into a treatise
upon the Elements of Chemistry.
The impossibility of separating the nomenclature of a science from the science
itself, is owing to this, that every branch of physical science must consist of three things;
the series of facts which are the objects of the science, the ideas which represent these
facts, and the words by which these ideas are expressed. Like three impressions of the
same seal, the word ought to produce the idea, and the idea to be a picture of the fact.
And, as ideas are preserved and communicated by means of words, it necessarily follows
that we cannot improve the language of any science without at the same time improving
the science itself; neither can we, on the other hand, improve a science, without
improving the language or nomenclature which belongs to it. However certain the facts of
any science may be, and, however just the ideas we may have formed of these facts, we
can only communicate false impressions to others, while we want words by which these
may be properly expressed.
To those who will consider it with attention, the first part of this treatise will
afford frequent proofs of the truth of the above observations. But as, in the conduct of my
work, I have been obliged to observe an order of arrangement essentially differing from
what has been adopted in any other chemical work yet published, it is proper that I should
1 [Lavoisier published his Traité Élementaire de Chimie in 1789. An English translation by Robert Kerr
was published in 1790 under the title Elements of Chemistry. The selections that appear in this manual are
taken from Kerr’s translation with slight modifications: the spelling and punctuation have been
modernized, some typographical errors have been corrected, and some minor changes have been made to
the translation.]
58
explain the motives which have led me to do so.
It is a maxim universally admitted in geometry, and indeed in every branch of
knowledge, that in the progress of investigation we should proceed from known facts to
what is unknown. In early infancy, our ideas spring from our wants; the sensation of want
excites the idea of the object by which it is to be gratified. In this manner, from a series of
sensations, observations, and analyses, a successive train of ideas arises, so linked
together that an attentive observer may trace back to a certain point the order and
connection of the whole sum of human knowledge.
When we begin the study of any science, we are in a situation, respecting that
science, similar to that of children; and the course by which we have to advance is
precisely the same which Nature follows in the formation of their ideas. In a child, the
idea is merely an effect produced by a sensation; and, in the same manner, in
commencing the study of a physical science, we ought to form no idea but what is a
necessary consequence, and immediate effect, of an experiment or observation. Besides,
he that enters upon the career of science, is in a less advantageous situation than a child
who is acquiring his first ideas. To the child, Nature gives various means of rectifying
any mistakes he may commit respecting the salutary or hurtful qualities of the objects
which surround him. On every occasion his judgments are corrected by experience; want
and pain are the necessary consequences arising from false judgment; gratification and
pleasure are produced by judging aright. Under such masters, we cannot fail to become
well informed; and we soon learn to reason justly, when want and pain are the necessary
consequences of a contrary conduct.
In the study and practice of the sciences it is quite different; the false judgments
we form neither affect our existence nor our welfare; and we are not forced by any
physical necessity to correct them. Imagination, on the contrary, which is ever wandering
beyond the bounds of truth, joined to self-love and that self-confidence we are so apt to
indulge, prompt us to draw conclusions which are not immediately derived from facts; so
that we become in some measure interested in deceiving ourselves. Hence it is by no
means to be wondered, that, in the science of physics in general, men have often made
suppositions, instead of forming conclusions. These suppositions, handed down from one
age to another, acquire additional weight from the authorities by which they are
supported, till at last they are received, even by men of genius, as fundamental truths.
The only method of preventing such errors from taking place, and of correcting
them when formed, is to restrain and simplify our reasoning as much as possible. This
depends entirely upon ourselves, and the neglect of it is the only source of our mistakes.
We must trust to nothing but facts: These are presented to us by Nature, and cannot
deceive. We ought, in every instance, to submit our reasoning to the test of experiment,
and never to search for truth but by the natural road of experiment and observation. Thus
mathematicians obtain the solution of a problem by the mere arrangement of data, and by
reducing their reasoning to such simple steps, to conclusions so very obvious, as never to
lose sight of the evidence which guides them.
Thoroughly convinced of these truths, I have imposed upon myself, as a law,
never to advance but from what is known to what is unknown; never to form any
conclusion which is not an immediate consequence necessarily flowing from observation
59
and experiment; and always to arrange the facts, and the conclusions which are drawn
from them, in such an order as shall render it most easy for beginners in the study of
chemistry thoroughly to understand them. Hence I have been obliged to depart from the
usual order of courses of lectures and of treatises upon chemistry, which always assume
the first principles of the science, as known, when the pupil or the reader should never be
supposed to know them till they have been explained in subsequent lessons. In almost
every instance, these begin by treating of the elements of matter, and by explaining the
table of affinities, without considering, that, in so doing, they must bring the principal
phenomena of chemistry into view at the very outset: They make use of terms which have
not been defined, and suppose the science to be understood by the very persons they are
only beginning to teach. It ought likewise to be considered, that very little of chemistry
can be learned in a first course, which is hardly sufficient to make the language of the
science familiar to the ears, or the apparatus familiar to the eyes. It is almost impossible
to become a chemist in less than three or four years of constant application.
These inconveniencies are occasioned not so much by the nature of the subject, as
by the method of teaching it; and, to avoid them, I was chiefly induced to adopt a new
arrangement of chemistry, which appeared to me more consonant to the order of Nature. I
acknowledge, however, that in thus endeavoring to avoid difficulties of one kind, I have
found myself involved in others of a different species, some of which I have not been
able to remove; but I am persuaded that such as remain do not arise from the nature of the
order I have adopted, but are rather consequences of the imperfection under which
chemistry still labors. This science still has many chasms, which interrupt the series of
facts, and often render it extremely difficult to reconcile them with each other: It has not,
like the elements of geometry, the advantage of being a complete science, the parts of
which are all closely connected together: Its actual progress, however, is so rapid, and the
facts, under the modern doctrine, have assumed so happy an arrangement, that we have
ground to hope, even in our own times, to see it approach near to the highest state of
perfection of which it is susceptible.
The rigorous law from which I have never deviated, of forming no conclusions
which are not fully warranted by experiment, and of never supplying the absence of facts,
has prevented me from comprehending in this work the branch of chemistry which treats
of affinities, although it is perhaps the best calculated of any part of chemistry for being
reduced into a completely systematic body. Messrs. Geoffroy, Gellert, Bergman, Scheele,
De Morveau, Kirwan, and many others, have collected a number of particular facts upon
this subject, which only wait for a proper arrangement; but the principal data are still
wanting, or, at least, those we have are either not sufficiently defined, or not sufficiently
proved, to become the foundation upon which to build so very important a branch of
chemistry. This science of affinities, or elective attractions, holds the same place with
regard to the other branches of chemistry, as the higher or transcendental geometry does
with respect to the simpler and elementary part; and I thought it improper to involve
those simple and plain elements, which I flatter myself the greatest part of my readers
will easily understand, in the obscurities and difficulties which still attend that other very
useful and necessary branch of chemical science.
Perhaps a sentiment of self-love may, without my perceiving it, have given
additional force to these reflections. Mr. de Morveau is at present engaged in publishing
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the article Affinity in the Methodical Encyclopedia; and I had more reasons than one to
decline entering upon a work in which he is employed.
It will, no doubt, be a matter of surprise, that in a treatise upon the elements of
chemistry, there should be no chapter on the constituent and elementary parts of matter;
but I shall take occasion, in this place, to remark that the fondness for reducing all the
bodies in nature to three or four elements proceeds from a prejudice which has descended
to us from the Greek Philosophers. The notion of four elements, which, by the variety of
their proportions, compose all the known substances in nature, is a mere hypothesis,
assumed long before the first principles of experimental philosophy or of chemistry had
any existence. In those days, without possessing facts, they framed systems; while we,
who have collected facts, seem determined to reject them, when they do not agree with
our prejudices. The authority of these fathers of human philosophy still carry great
weight, and there is reason to fear that it will even bear hard upon generations yet to
come.
It is very remarkable that, notwithstanding of the number of philosophical
chemists who have supported the doctrine of the four elements, there is not one who has
not been led by the evidence of facts to admit a greater number of elements into their
theory. The first chemists that wrote after the revival of letters, considered sulfur and salt
as elementary substances entering into the composition of a great number of substances;
hence, instead of four, they admitted the existence of six elements. Beccher assumes the
existence of three kinds of earth, from the combination of which, in different proportions,
he supposed all the varieties of metallic substances to be produced. Stahl gave a new
modification to this system; and succeeding chemists have taken the liberty to make or to
imagine changes and additions of a similar nature. All these chemists were carried along
by the influence of the genius of the age in which they lived, which contented itself with
assertions without proofs; or, at least, often admitted as proofs the slighted degrees of
probability, unsupported by that strictly rigorous analysis required by modern philosophy.
All that can be said upon the number and nature of elements is, in my opinion,
confined to discussions entirely of a metaphysical nature. The subject only furnishes us
with indefinite problems, which may be solved in a thousand different ways, not one of
which, in all probability, is consistent with nature. I shall therefore only add upon this
subject, that if, by the term elements, we mean to express those simple and indivisible
atoms of which matter is composed, it is extremely probable we know nothing at all
about them; but, if we apply the term elements, or principles of bodies, to express our
idea of the last point which analysis is capable of reaching, we must admit, as elements,
all the substances into which we are capable, by any means, to reduce bodies by
decomposition. Not that we are entitled to affirm, that these substances we consider as
simple may not be compounded of two, or even of a greater number of principles; but,
since these principles cannot be separated, or rather since we have not hitherto discovered
the means of separating them, they act with regard to us as simple substances, and we
ought never to suppose them compounded until experiment and observation has proved
them to be so.
The foregoing reflections upon the progress of chemical ideas naturally apply to
the words by which these ideas are to be expressed. Guided by the work which, in the
year 1787, Messrs. de Morveau, Berthollet, de Fourcroy, and I composed upon the
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Nomenclature of Chemistry, I have endeavored, as much as possible, to denominate
simple bodies by simple terms, and I was naturally led to name these first. It will be
recollected that we were obliged to retain that name of any substance by which it had
been long known in the world, and that in two cases only we took the liberty of making
alterations; first, in the case of those which were but newly discovered, and had not yet
obtained names, or at least which had been known but for a short time, and the names of
which had not yet received the sanction of the public; and, secondly, when the names
which had been adopted, whether by the ancients or the moderns, appeared to us to
express evidently false ideas, when they confounded the substances, to which they were
applied, with others possessed of different, or perhaps opposite qualities. We made no
scruple, in this case, of substituting other names in their room, and the greatest number of
these were borrowed from the Greek language. We endeavored to frame them in such a
manner as to express the most general and the most characteristic quality of the
substances; and this was attended with the additional advantage both of assisting the
memory of beginners, who find it difficult to remember a new word which has no
meaning, and of accustoming them early to admit no word without connecting with it
some determinate idea.
To those bodies which are formed by the union of several simple substances we
gave new names, compounded in such a manner as the nature of the substances directed;
but, as the number of double combinations is already very considerable, the only method
by which we could avoid confusion, was to divide them into classes. In the natural order
of ideas, the name of the class or genus is that which expresses a quality common to a
great number of individuals: The name of the species, on the contrary, expresses a quality
peculiar to certain individuals only.
These distinctions are not, as some may imagine, merely metaphysical, but are
established by Nature. “A child,” says the Abbé de Condillac, “is taught to give the name
tree to the first one which is pointed out to him. The next one he sees presents the same
idea, and he gives it the same name. This he does likewise to a third and a fourth, till at
last the word tree, which he first applied to an individual, comes to be employed by him
as the name of a class or a genus, an abstract idea, which comprehends all trees in
general. But, when he learns that all trees serve not the same purpose, that they do not all
produce the same kind of fruit, he will soon learn to distinguish them by specific and
particular names.” This is the logic of all the sciences, and is naturally applied to
chemistry.
The acids, for example, are compounded of two substances, of the order of those
which we consider as simple; the one constitutes acidity, and is common to all acids, and,
from this substance, the name of the class or the genus ought to be taken; the other is
peculiar to each acid, and distinguishes it from the rest, and from this substance is to be
taken the name of the species. But, in the greatest number of acids, the two constituent
elements, the acidifying principle, and that which it acidifies, may exist in different
proportions, constituting all the possible points of equilibrium or of saturation. This is the
case in the sulfuric and the sulfurous acids; and these two states of the same acid we have
marked by varying the termination of the specific name.
Metallic substances which have been exposed to the joint action of the air and of
fire, lose their metallic luster, increase in weight, and assume an earthy appearance. In
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this state, like the acids, they are compounded of a principle which is common to all, and
one which is peculiar to each. In the same way, therefore, we have thought proper to class
them under a generic name, derived from the common principle; for which purpose we
adopted the term oxide; and we distinguish them from each other by the particular name
of the metal to which each belongs.
Combustible substances, which in acids and metallic oxides are a specific and
particular principle, are capable of becoming, in their turn, common principles of a great
number of substances. The sulfurous combinations have been long the only known ones
in this kind. Now, however, we know, from the experiments of Messrs. Vandermonde,
Monge, and Berthollet, that charcoal may be combined with iron, and perhaps with
several other metals; and that, from this combination, according to the proportions, may
be produced steel, plumbago, &c. We know likewise, from the experiments of M.
Pelletier, that phosphorus may be combined with a great number of metallic substances.
These different combinations we have classed under generic names taken from the
common substance, with a termination which marks this analogy, specifying them by
another name taken from that substance which is proper to each.
The nomenclature of bodies compounded of three simple substances was attended
with still greater difficulty, not only on account of their number, but, particularly, because
we cannot express the nature of their constituent principles without employing more
compound names. In the bodies which form this class, such as the neutral salts, for
instance, we had to consider, 1st, The acidifying principle, which is common to them all;
2d, The acidifiable principle which constitutes their peculiar acid; 3d, The saline, earthy,
or metallic basis, which determines the particular species of salt. Here we derived the
name of each class of salts from the name of the acidifiable principle common to all the
individuals of that class; and distinguished each species by the name of the saline, earthy,
or metallic basis, which is peculiar to it.
A salt, though compounded of the same three principles, may, nevertheless, by the
mere difference of their proportion, be in three different states. The nomenclature we
have adopted would have been defective, had it not expressed these different states; and
this we attained chiefly by changes of termination uniformly applied to the same state of
the different salts.
In short, we have advanced so far, that from the name alone may be instantly
found what the combustible substance is which enters into any combination; whether that
combustible substance be combined with the acidifying principle, and in what proportion;
what is the state of the acid; with what basis it is united; whether the saturation be exact,
or whether the acid or the basis be in excess.
It may be easily supposed that it was not possible to attain all these different
objects without departing, in some instances, from established custom, and adopting
terms which at first sight will appear uncouth and barbarous. But we considered that the
ear is soon habituated to new words, especially when they are connected with a general
and rational system. The names, besides, which were formerly employed, such as powder
of algaroth, salt of alembroth, pompholix, phagadenic water, turbith mineral, colcathar,
and many others, were neither less barbarous nor less uncommon. It required a great deal
of practice, and no small degree of memory, to recollect the substances to which they
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were applied, much more to recollect the genus of combination to which they belonged.
The names of oil of tartar per deliquium, oil of vitriol, butter of arsenic and of antimony,
flowers of zinc, &c. were still more improper, because they suggested false ideas: For, in
the whole mineral kingdom, and particularly in the metallic class, there exists no such
thing as butters, oils, or flowers; and, in short, the substances to which they give these
fallacious names, are nothing less than rank poisons.
When we published our essay on the nomenclature of chemistry, we were
reproached for having changed the language which was spoken by our masters, which
they distinguished by their authority, and handed down to us. But those who reproach us
on this account have forgotten that it was Bergman and Macquer themselves who urged
us to make this reformation. In a letter which the learned Professor of Upsal, M.
Bergman, wrote, a short time before he died, to M. de Morveau, he bids him spare no
improper names; those who are learned, will always be learned, and those who are
ignorant will thus learn sooner.
There is an objection to the work which I am going to present to the public, which
is perhaps better founded, that I have given no account of the opinion of those who have
gone before me; that I have stated only my own opinion, without examining that of
others. By this I have been prevented from doing that justice to my associates, and more
especially to foreign chemists, which I wished to render them. But I beseech the reader to
consider, that, if I had filled an elementary work with a multitude of quotations; if I had
allowed myself to enter into long dissertations on the history of the science, and the
works of those who have studied it, I must have lost sight of the true object I had in view,
and produced a work, the reading of which must have been extremely tiresome to
beginners. It is not to the history of the science, or of the human mind, that we are to
attend in an elementary treatise: Our only aim ought to be ease and perspicuity, and with
the utmost care to keep every thing out of view which might draw aside the attention of
the student; it is a road which we should be continually rendering more smooth, and from
which we should endeavor to remove every obstacle which can occasion delay. The
sciences, from their own nature, present a sufficient number of difficulties, though we
add not those which are foreign to them. But, besides this, chemists will easily perceive,
that, in the first part of my work, I make very little use of any experiments but those
which were made by myself: If at any time I have adopted, without acknowledgment, the
experiments or the opinions of M. Berthollet, M. Fourcroy, M. de la Place, M. Monge, or,
in general, of any of those whose principles are the same with my own, it is owing to this
circumstance, that frequent intercourse, and the habit of communicating our ideas, our
observations, and our way of thinking to each other, has established between us a sort of
community of opinions, in which it is often difficult for everyone to know his own.
The remarks I have made on the order which I thought myself obliged to follow in
the arrangement of proofs and ideas are to be applied only to the first part of this work. It
is the only one which contains the general sum of the doctrine I have adopted, and to
which I wished to give a form completely elementary.
The second part is composed chiefly of tables of the nomenclature of the neutral
salts. To these I have only added general explanations, the object of which was to point
out the most simple processes for obtaining the different kinds of known acids. This part
contains nothing which I can call my own, and presents only a very short abridgment of
64
the results of these processes, extracted from the works of different authors.
In the third part, I have given a description, in detail, of all the operations
connected with modern chemistry. I have long thought that a work of this kind was much
wanted, and I am convinced it will not be without use. The method of performing
experiments, and particularly those of modern chemistry, is not so generally known as it
ought to be; and had I, in the different memoirs which I have presented to the Academy,
been more particular in the detail of the manipulations of my experiments, it is probable I
should have made myself better understood, and the science might have made a more
rapid progress. The order of the different matters contained in this third part appeared to
me to be almost arbitrary; and the only one I have observed was to class together, in each
of the chapters of which it is composed, those operations which are most connected with
one another. I need hardly mention that this part could not be borrowed from any other
work, and that, in the principal articles it contains, I could not derive assistance from
anything but the experiments which I have made myself.
I shall conclude this preface by transcribing, literally, some observations of the
Abbé de Condillac, which I think describe, with a good deal of truth, the state of
chemistry at a period not far distant from our own. These observations were made on a
different subject; but they will not, on this account, have less force, if the application of
them be thought just.
“Instead of applying observation to the things we wished to know, we have
chosen rather to imagine them. Advancing from one ill-founded supposition to another,
we have at last bewildered ourselves amidst a multitude of errors. These errors becoming
prejudices, are, of course, adopted as principles, and we thus bewilder ourselves more
and more. The method, too, by which we conduct our reasonings is as absurd; we abuse
words which we do not understand, and call this the art of reasoning. When matters have
been brought this length, when errors have been thus accumulated, there is but one
remedy by which order can be restored to the faculty of thinking; this is, to forget all that
we have learned, to trace back our ideas to their source, to follow the train in which they
rise, and, as my Lord Bacon says, to frame the human understanding anew.”
“This remedy becomes the more difficult in proportion as we think ourselves
more learned. Might it not be thought that works which treated of the sciences with the
utmost perspicuity, with great precision and order, must be understood by everybody?
The fact is, those who have never studied anything will understand them better than those
who have studied a great deal, and especially than those who have written a great deal.”
At the end of the fifth chapter, the Abbé de Condillac adds: “But, after all, the
sciences have made progress, because philosophers have applied themselves with more
attention to observe, and have communicated to their language that precision and
accuracy which they have employed in their observations: In correcting their language
they reason better.”
65
Louis de Morveau
Memoir on Chemical Names1
First Principle: A phrase is not a name; chemicals and chemical products should
have names that denominate them on all occasions, without recourse to circumlocutions.
Second Principle: Denominations should, as far as possible, conform to nature of
things.
(Corollaries) Firstly, the substantive name preferably belongs to the simplest
object, to the entire, unaltered object, and the expression that modifies it and makes it
specific should be placed as an epithet, or in a similar manner.
Secondly, the denomination of a chemical compound is only clear and exact in as
much as it recalls the constituent parts by names conforming to their nature.
Thirdly, the names of discoverers that cannot conform with any things, either
individual or generic, should be forbidden from all important nomenclature.
Third Principle: When we have no certain understanding of the character that
ought chiefly to determine the denomination, a name that expresses nothing is preferable
to one which may express a false idea.
Fourth Principle: In choosing new denominations, those having roots from the
most widespread dead languages should be preferred in order that the word may easily be
recalled by the sense and the sense by the word.
Fifth Principle: Denominations should be matched with care with regard to the
genius of the language for which they are formed.
1 [This is an edited form of Morveau’s rules for the establishment of a new nomenclature as they appeared
in his Memoir on Chemical Names, the Necessity for Perfecting the System,the Rules for Attaining it,
Followed by a Table of Chemical Nomenclature, published in 1782. The explanatory text has been
omitted.]
66
Morveau, Lavoisier, Claude Berthollet, and Antoine de Fourcroy
Method of Chemical Nomenclature1
The principles of which the general exposition was contained in the memoir of Mr.
Lavoisier without doubt are sufficient to justify our design of reforming the chemical
nomenclature; these principles have appeared to us to carry with them such convictions
as cannot fail to acquire universal approbation, after which it would seem that we had
nothing more to do but present to the Academy the result of our common labor, or the
synopsis formed according to those principles. But we were of opinion that it was
incumbent on us to give an account to the Academy of the reasons that have directed us,
and even thereby to acquire information to determine us in the choice of the principal
denominations; that it especially was of importance to the success of the undertaking to
surmount the difficulties of retaining and hearing the new denominations by reducing to a
single sheet the entire system containing all the necessary examples for the formation of
compound names; in fine, that it was necessary to add to it the Latin version of the new
nomenclature, thereby to demonstrate how this system when once adopted would become
agreeable to every idiom, and to contribute as much as possible to the regulation of that
uniformity of language that is so essentially necessary to the communication of
discoveries and to the progress of the science.
Such are the subjects of the present memoir, which shall be no more than the
expression of the unanimous wish, and the result of all the discussions and conferences
that we have had on the subject. When I published an essay on the chemical
nomenclature in the Journal de Physique for the month of May 1782, I did not think that
the simple merit of having perceived the necessity of correcting the nomenclature would
at this day have procured me the satisfaction of being occupied with some of the
members of the Academy, of being charged by them to present the plan, and to be able to
gain that kind attention that the Academy has always been pleased to show.
In the order which we have proposed to ourselves, the simple substances, that is to
say, such as chemists to the present time have not been able to decompose, ought chiefly
to fix our attention, because the denominations of bodies that by exact analysis can be
reduced to their elements are properly expressed by the re-union of the names of those
same principles.
The substances that we have not as yet been able to decompose may be divided
into five classes.
The first class contains the principles that, without presenting any remarkable
analogy with each other, have notwithstanding one thing in common, that is to say, that
they appear to approach the nearest to a state of simplicity, which makes them resist all
further analysis, and at the same time renders them so active in their combinations.
The second class includes all the acidifiable bases or radical principles of the
acids.
In the third class we place all the substances whose remarkable characteristic is to
appear in a metallic form.
The fourth contains all the different earths.
1 [Published in 1787.]
67
The fifth is occupied by the alkalis.
After these five classes we shall indicate in an appendix the more compound
bodies, which, combining as simple substances or without undergoing any sensible
decomposition, have appeared to us worthy of occupying a place in the methodical
nomenclature for the completion of the system.
We shall here give some general notions of each of these classes.
FIRST SECTION:
OF THE SUBSTANCES THAT APPROACH NEAREST TO A STATE OF
SIMPLICITY
The substances of the first class are five in number: light, matter of heat,
dephlogisticated air or vital air, inflammable gas, and phlogisticated air; this last shall be
placed in the nomenclature among the acidifiable bases, because it is really the basis of
nitrous acid; but it is evident that it also possesses properties of a different nature, which
induce us to place it in this class.
Light and heat appear in many circumstances to be productive of the same effects;
but as our knowledge is not perfect enough to be able to determine their identity or their
difference, we have preserved for each its particular name: We have supposed that we
ought to distinguish heat only, which is generally thought to be a sensation produced by a
material principle, and we have expressed this latter by the word caloric. Thus we shall
say that the caloric passed from one body into another without producing a sensible heat,
or that the caloric produced heat, etc. This manner of expression will be as clear, and will
cause less embarrassment in discourse than that of the matter of heat, which the necessity
of speaking so as to be understood has for some time past introduced.
When the appellation of dephlogisticated air was changed into that of vital air, a
choice more agreeable to reason was made, by substituting for an expression founded
upon mere hypothesis, a term derived from one of the most remarkable properties of that
substance, and which is so essentially characteristic of it that one should never hesitate to
use it whenever it be necessary to indicate simply that portion of the atmospherical air
that maintains respiration and combustion; but it is at present well demonstrated that this
portion of the atmospherical fluid is not always present in the state of air or gas, that it is
decomposed in a great many operations, and loses, at least in part, the light and caloric
that are what principally constitute it vital air; this substance should be considered and
represented in that state of its greatest simplicity; the logic of the nomenclature requires
even that it be named the first, that the word that would recall the idea become the model
for the denominations of its compounds. We have agreed to those conditions by adopting
the word oxygen, deriving it, as Mr. Lavoisier proposed, from the Greek words
(oxys) acid, and (geinomai) I beget,2 on account of the property of this
principle, the basis of vital air, to change a great many of the substances with which it
unites into the state of acid, or rather because it appears to be a principle necessary to
2 [The first meaning of the Greek word (oxys) is “sharp,” applied to stones, sounds, and flavors, and
thence it also came to mean “sour,” from which it was applied to the sharp-tasting or sour corrosive
substances. (Note that the German for oxygen is Sauerstoff, literally, “sour substance.” Lavoisier implicitly
notes this origin of the name in Elements of Chemistry (p. 101). Note also that geinomai) is the
passive infinitive “to be begotten,” whereas (gennao) is “I beget.”]
68
acidity. We shall therefore say that vital air is oxygen gas, and that oxygen unites with
sulfur, and with phosphorous during their combustion, and to metals in their calcination,
etc., and this language will be at the same time both exact and perspicuous.
On applying the same principles to the aeriform substance called inflammable
gas, the necessity of having a more explicit appellation is evident at the first view; it is
true that this fluid is capable of being consumed, but this property does not exclusively
belong to it, notwithstanding that it is the only substance that produces water by its
combustion with oxygen gas. This is the property that appeared to us to be the most
worthy of affording a name, but not for the oxygen gas itself, which is a composition, but
for the more fixed principle that constitutes the basis, and we have therefore called it
hydrogen, from ‘ (hydor) water and (geinomai) I beget; experiments
having proved that water is nothing but oxygenated hydrogen, or the immediate
production of the combustion of oxygen gas with hydrogen gas, deprived of the light and
caloric that disengage during the combustion.
The denomination of phlogisticated air has been abandoned by the greater
number of chemists who thought that it expressed more than it ought, even a long time
before it was known to express an error. It is at present well known that this fluid, which
makes so considerable a part of the atmospherical air, is not vitiated vital air; that it has
nothing in common with respirable air but its state of elastic fluidity, which is caused by
its union with caloric: in short, that in losing this state of gas it becomes an element
proper to many combinations. As there are several proofs of its being a distinct substance,
a particular name for it was necessary, and in searching for one we endeavored to avoid
at the same time the inconvenience of one of those perfectly insignificant words that are
not connected with any known idea, and that offer no hold to the memory, and the
inconvenience, perhaps the more considerable, of prematurely affirming what has been
only foreseen.
It results from some synthetical experiments made by the Hon. Mr. Cavendish,
and confirmed by a great number of analyses, that this principle is a component part of
the nitrous acid. Mr. Berthollet has proved its existence in the volatile alkali,3 and in
animal substances; it is probable that the fixed alkali also contains it, and from this it
appears to deserve the appellation of alkali-gen, as was proposed by Mr. de Fourcroy. But
the analysis of these compositions is not sufficiently advanced to determine positively the
manner of existence of this principle in those different substances, and from thence to
attribute to it a constant and uniform property; besides, it was not possible by a single
word to express the double property of forming the radical of a certain acid, and assisting
in the production of an alkali; there did not appear any reasons for considering the latter
of these properties in preference to the former, and by admitting the one in a manner to
exclude the other. In this situation we thought it were the better way to derive the
denomination from its other property, which it manifests in a very great degree, viz. not
to maintain the existence of animals, to be really non-vital; in short, to be so in a more
considerable respect than the hepatic and acid gases, which do not like it constitute an
essential part of the atmospherical mass, and therefore we have denominated it azot from
the Greek privative (a) and (zoe) life. After this it may not appear difficult to
remember that the air that we breathe is a composition of oxygen gas and azotic gas.
3 [What we now call “ammonia.” This highly toxic gas is derived from from sal ammoniac (also called “salt
of Ammon”), a salt first found in large quantities near the temple of Ammon in Egypt.]
69
SECOND SECTION:
OF THE ACIDIFIABLE BASES OR RADICAL PRINCIPLES OF THE ACIDS
The class of the substances whose principal characteristic is to be capable of
being transformed into the state of acid is much more extensive; but at the same time it
has more uniformity, and the considering of a few substances and the following of them
in their various compositions is sufficient to give a perfect idea of all this part of the
nomenclature.
In this class are to be distinguished the acids whose acidifiable bases have not as
yet been separated by chemical process from the general acidifying principle.
The acidifiable bases that are known are azot, the basis of the nitrous acid, which
we have mentioned in the preceding section, charcoal, sulfur, and phosphorus. On these
bases we have established the method of naming, because their combinations are the most
numerous, the most familiar to us, and the most easy to follow; as to the others, the base
of the marine acid, of the acid of borax, of the acid of vinegar etc., we have only
expressed the simple substance of each acid that modifies the oxygen by the expression
of acidifiable base, or, for more conciseness, radical of the acid; thereby to continue the
same analogy, and to be able to consider each of these substances in order and in an
abridged manner, without hazarding anything on their essential properties until they shall
have been discovered and proved by decisive experiments. It is probable that many of
these acids have compound bases, or that they differ from one another merely by the
diversity of proportion of the same principles: When their elements and the order of their
descent shall be discovered by exact analyses, it will without doubt be necessary to
reduce them to their proper situations, but nevertheless it therefore shall not be thought
useless to study their properties and attractions in their present compound state, and
therefore we cannot avoid giving them a place in the system of our nomenclature.
Those things being premised, let us take for example sulfur, or in other words the
acidifiable base of vitriolic acid, which is the third in the class; the numerous productions
of its combinations, known this long time past, will enable us to explain the rules that we
have formed, and follow the application in the most advantageous manner, to show the
progress of the compositions and the general system of the table.
Sulfur by combining with oxygen produces an acid: It is evident that to preserve
the idea of this oxygen, and to express clearly the first degree of composition, the name
of the acid should be derived from the name of its base; but this acid presents itself in two
states of saturation, and therefore manifests different properties. That they should not be
confounded, a name ought to be given to each of these states, which always retaining its
primitive root, would yet express this difference: And the same should be done for the
salts formed by these two acids; after this the other direct combinations should be
considered: The five different states of the same principle are expressed by as many
different terminations adapted to the same original word, in the manner that appeared to
us least inharmonious to the ear.
Sulfuric acid signifies sulfur as much as possible saturated with oxygen; which
composition was formerly called vitriolic acid.
Sulfureous acid means sulfur united to a lesser quantity of oxygen; which before
was called volatile sulfurous vitriolic acid, or phlogisticated vitriolic acid.
70
Sulfat is the general name for all the salts formed by sulfuric acid.
Sulfite signifies the salts formed by the sulfureous acid.
Sulfuret denominates all the combinations of sulfur not advanced to the state of
acid, and regularly displaces the improper and absurd appellations of liver of sulfur,
hepar, pyrite, etc.
Every one must perceive, at the first glance, all the advantages of such a
nomenclature, which at the same time that it indicates the different substances, defines
them, points out their constituent principles, classes them in their order of composition,
and indicates, in a manner, even the proportions that diversify their properties.
Some persons perhaps may be astonished that we should not include in this
reformation the words vitriolic acid and vitriol, which custom appears to have rendered
sacred; in reality, it is the most considerable innovation, and the only one of the kind to
be found in the whole nomenclature: We have felt all the force of the objection, we have
considered it for a long time, and we would not have hesitated to suffer these words,
although improper, to remain, through respect for established custom, if we were to
consider them only in respect to themselves; but it was necessary to form a system for the
entire class of acids, a class the most numerous and important; and surely no person will
reproach us for not having sacrificed all the advantages of this method to the preservation
of the word vitriol. Precisely it is because the acid formed by sulfur is that which is the
most frequently employed, which enters into the greatest number of compositions, and
especially because it is that which learners first begin to study, that we judged it the more
necessary to be submitted to the rigorous application of our rules, thereby that it might
serve to facilitate the study of the other acids by an agreeable conformity. Instead of
creating a new word, we had only to modify by a new termination of the word sulfur,
which has been for a long time admitted by every chemist. We have likewise considered
that the words vitriolic acid, vitriol of iron, and vitriol of zinc, are expressions of spirit of
sulfur, green copperas, white copperas, etc., and we take it for granted that the chemists
who already have abandoned these latter terms, will at present voluntarily surrender a few
terms to render the language of chemistry pure and uniform.
As to the other acids, we had much less to do in reducing their appellations to our
systematical rules, as is evident from the words nitrous acids, tartareous acid,
phosphoric acid, etc.
There is no substance whatever that has received so many different appellations as
the gas that Dr. Black has called fixed air; at the same time expressly reserving the liberty
of changing the denomination, which he confessed was improperly applied. The
disagreement of the chemists of every country gives us, without doubt, a more perfect
liberty, because it shows the necessity of motives being presented capable of making
them all unanimous: And we have made use of that liberty according to our principles. As
fixed air has been perceived to be produced by the direct combination of charcoal and
vital air, by the assistance of combustion, the name of this gaseous acid can no longer be
arbitrary, but necessarily must be derived from its radical, which is the pure carbonic
matter; therefore it is called carbonic acid,4 and its compositions with different bases are
carbonats, and, for the sake of greater precision in the demonstration of this radical, by
distinguishing it from charcoal, according to the vulgar acceptance, in idea to isolate it
4 [Carbonic acid (gas) is the most highly oxygenated form of carbon.]
71
from the small quantity of foreign matter that it generally contains, and which constitutes
the ashes, we adapt to it the modified name carbon,5 which indicates the pure and
essential principle of charcoal, and which has the advantage of expressing it by a single
word, so as to prevent all equivocation.
Plumbago, which is only iron united to charcoal, shall take the appellation of
carburet of iron, according to the established analogy.
Muriatic acid, derived from the Latin muria, muriaticum, has already taken the
place of marine acid in the writings of several chemists; but it is well known that it is an
acid of a particular nature, because it imbibes an excess of oxygen, and because in this
state its acidity seems rather to decrease than to augment, which perhaps is occasioned by
the oxygen’s retaining in that combination a greater quantity of caloric. Whatever be the
cause of this phenomenon, it was necessary that it have a denomination appropriated to
so particular a property, which to the present time has been very falsely expressed by the
term dephlogisticated marine acid. The appellations of oxygenated muriatic acid, and
oxygenated muriats have appeared to us more simple and more conformable to our
intention of not expressing any more than the most positive facts. Likewise according to
this rule, we have formed the names of all the other combinations of the muriatic acid:
Thus corrosive sublimate, becomes corrosive mercurial muriat; the mercurious dulcis,
mild mercurial muriat; the salt produced by the dissolution of tin in this acid, muriat of
tin; the butter of tin, sublimated muriat of tin; Libavius’s liquor, smoking muriat of tin,
etc.
Analogy induces us to think that the muriatic acid has an acidifiable base, as well
as the carbonic, sulfuric, and phosphoric acids, which, like the bases of these latter,
serves to give a distinct and particular property to the product of a combination of
oxygen. We could not express this substance otherwise than by the name of muriatic
radical or muriatic radical principle; in fine, that a name should not be given to an
unknown substance, and that the expression should be limited to the simple property with
which we are acquainted, and which is to produce this acid. We have had the same
caution in respect to the other acids with which we are not yet well acquainted, some of
whose bases will probably be discovered in the substances that we have already named.
We are obliged to include in this class even the bases of the vegetable and animal acids,
of which we have not as yet any exact analysis, notwithstanding the facility with which
they are reduced to their elements.
The nature of the acidifiable base being independent of the proportion in which it
be united to the oxygen, it is evident that the sulfur is at the same time sulfuric radical,
and sulfureous radical: But it was also necessary to render that expression uniform for all
the acids; and we have gone no farther than the first termination, which signifies the most
complete saturation of the acidifiable base. Thus we say boracic radical, and even
tartaric radical, etc., although we are acquainted only with the tartareous acid, which is
the tartaric radical united to a very small portion of oxygen, if we can judge from all that
has as yet been observed in the phenomena of its combustion.
The choice of the one or the other of these terminations became very important to
indicate, in the combinations of the acids themselves, the different degrees of saturation.
As soon as they were known we have not hesitated to make the authority of the rule
5 [The French word being proposed here is carbone, a “modified” version of charbon, the French word for
charcoal.]
72
prevail over that of the custom by naming, for example, nitrous acid for that much
weaker acid where the same base is united to a much less quantity of oxygen.
According to this analogy, phlogisticated or volatile phosphoric acid becomes
phosphorus acid; the experiments of Mr. Berthollet upon radical vinegar having
demonstrated that it was no more than the common vinegar saturated with oxygen, we
thought it proper to distinguish the acetic acid and the acetous acid. This distinction,
being once established, has afforded us the nitrats and the nitrites, the phosphats and the
phosphites, the acetats, and the acetites, as has been shown in the denomination of the
salts formed by the acid of sulfur: The word nitre is the only exception, which, through
respect to custom, we have retained as synonymous with nitrat of potash . . .
73
Notes on the Reading
1. It is not intended that your discussion will concentrate on the details of the new
nomenclature. But you should study the details in order that you may read with comfort
the subsequent papers in this laboratory—all of them use the new nomenclature. You will
find most of the basic “vocabulary” you will need in Lavoisier’s Preface, Morveau’s
“Method of Chemical Nomenclature” (much of which is repeated by Lavoisier), and in
the note below.
2. The committee on nomenclature chaired by Morveau had Lavoisier as its leading
member. The system devised by Lavoisier is basically the one used today. Below are
some of the changes in, or additions to, the system, which will be of use to you in
subsequent readings:
(a) Some of the changes in spelling: from “sulfureous” to “sulfurous”, “nitrats” to
“nitrates”, “phosphats” to “phosphates”, “acetats” to “acetates”, and “carbonats”
to “carbonates”.
(b) The first and second classes (omitting caloric and light) mentioned in Morveau’s
memoir together constitute what are now called the non-metals.
(c) About the year 1800 it was decided that those new elements discovered which
had metallic properties would have a stem name given according to the
idiosyncracy of the discoverer but always with the ending: -ium: potassium,
sodium, magnesium, germanium, etc. Those newly discovered elements that
were non-metals were to have the ending -on: boron, silicon, neon, etc. The only
exceptions to this latter rule occurred in naming the group of elements obtained
by decomposing sea salts and were known as the halogens (halys = salt,
genesthai = producer). These were given names ending in -ine: fluorine, chlorine,
bromine, and iodine. This system of naming was not retroactive. Those
substances established by Lavoisier as elements that continued to be so
considered kept the names he established for them.1
(d) When a substance is formed by the combination of only two elements (called a
binary substance), the metallic element is named first with its usual full name.
The second element is then named, but with its stem plus the ending -ide; e.g.,
zinc chloride, lead sulfide, silver oxide, etc. There are only a few binary
substances formed from two metals. There are many binary substances formed
from a metal and a non-metal, or a non-metal and another non-metal. If the
binary substance is composed of two non-metals and one is oxygen, then it is an
oxide; e.g., carbon oxide. The ending -et, as in carburet of iron, is no longer used.
(e) Following a later trend of naming by putting the name of the metallic element
present first, such names as “sulfate of zinc” became, by convention, “zinc
sulfate”.
(f) The change in the name of the substance here called “oxygenated muriatic acid”
(Morveau, et al., p. 71) will be considered when we discuss the “Acidifying
Principle” later in Chapter II.
(g) The endings -ic and -ous (Morveau et al., p. 69) are not limited to specifying
binary substances having different degrees of oxygenation. The -ic ending is
added to the stem name of the first element (sometimes modified, as with copper
below) to indicate that it has a lower weight ratio to the second element
combined with it than has the -ous ending substance. Thus cupric sulfide has a
lower weight ratio of copper to sulfur than has cuprous sulfide; mercuric chloride
has a lower weight ratio of mercury to chlorine than has mercurous chloride; etc.
1 For the etymology of the names of the elements, see W.E. Floo, The Origin of Chemical Names (1963).
74
(h) Shortly after Morveau et al. published this essay, “fixed air,” the newly renamed
element “azot,” came to be called “azote.” Cavendish named this substance
“nitrogen”—“I beget nitre”—although this name did not come into common use
in English until a few decades later. See, for example, Dalton’s table of elements
on p. 138 (1808), where the word “azote” is still in use. In France it is still called
“azote.” In German it is “Stickstoff,” literally, “suffocating substance.”
3. Heat is not now considered to be a substance, and the term indicating “the matter of
heat,” caloric, is no longer used. However, we still measure heat in calorimeters and the
calorie is the most common unit of heat. The history of the abandonment of the caloric
theory is a fascinating and important story but not especially relevant to our concerns
here, although you will read two papers presenting experimental evidence that heat is not
substance (see pp. 87-91). If you wish to study this issue on your own initiative, you
might start with Harvard Case Histories in Experimental Science, No. 3, “The Rise and
Decline of Caloric Theory.”
Questions and Problems
1. Consider the role measurement plays in Lavoisier’s classification of substances.
2. What presuppositions do these scientists make about the role of language in science?
3. In what way is Lavoisier rejecting Aristotle? In what way agreeing with him?
* * * * *
75
Lavoisier
Elements of Chemistry
PART I
CHAPTER I.
Of the Combinations of Caloric, and the Formation of Elastic Aeriform Fluids.
That every body, whether solid or fluid, is augmented in all its dimensions by any
increase of its sensible heat, was long ago fully established as a physical axiom or
universal proposition by the celebrated Boerhaave. Such facts as have been adduced for
controverting the generality of this principle offer only fallacious results, or, at least, such
as are so complicated with foreign circumstances as to mislead the judgment: But, when
we separately consider the effects, so as to deduce each from the cause to which they
separately belong, it is easy to perceive that the separation of particles by heat is a
constant and general law of nature.
When we have heated a solid body to a certain degree, and have thereby caused
its particles to separate from each other, if we allow the body to cool, its particles again
approach each other in the same proportion in which they were separated by the increased
temperature; the body returns through the same degrees of expansion which it before
extended through; and, if it be brought back to the same temperature from which we set
out at the commencement of the experiment, it recovers exactly the same dimensions
which it formerly occupied. But, as we are still very far from being able to arrive at the
degree of absolute cold, or deprivation of all heat, being unacquainted with any degree of
coldness which we cannot suppose capable of still farther augmentation, it follows that
we are still incapable of causing the ultimate particles of bodies to approach each other as
near as is possible; and, consequently, that the particles of all bodies do not touch each
other in any state hitherto known, which, though a very singular conclusion, is yet
impossible to be denied.
It is supposed, that, since the particles of bodies are thus continually impelled by
heat to separate from each other, they would have no connection between themselves;
and, of consequence, that there could be no solidity in nature, unless they were held
together by some other power which tends to unite them, and, so to speak, to chain them
together; which power, whatever be its cause, or manner of operation, we name
Attraction.
Thus the particles of all bodies may be considered as subjected to the action of
two opposite powers, the one repulsive, the other attractive, between which they remain
in equilibrium. So long as the attractive force remains stronger, the body must continue in
a state of solidity; but if, on the contrary, heat has so far removed these particles from
76
each other as to place them beyond the sphere of attraction, they lose the adhesion they
before had with each other, and the body ceases to be solid.
Water gives us a regular and constant example of these facts; whilst below Zero1
of the French thermometer, or 32° of Fahrenheit, it remains solid, and is called ice.
Above that degree of temperature, its particles being no longer held together by
reciprocal attraction, it becomes liquid; and, when we raise its temperature above 80°
(212°), its particles, giving way to the repulsion caused by the heat, assume the state of
vapor or gas, and the water is changed into an aeriform fluid.
The same may be affirmed of all bodies in nature: They are either solid or liquid,
or in the state of elastic aeriform vapor, according to the proportion which takes place
between the attractive force inherent in their particles, and the repulsive power of the heat
acting upon these; or, what amounts to the same thing, in proportion to the degree of heat
to which they are exposed.
It is difficult to comprehend these phenomena, without admitting them as the
effects of a real and material substance, or very subtle fluid, which, insinuating itself
between the particles of bodies, separates them from each other; and, even allowing the
existence of this fluid to be hypothetical, we shall see in the sequel, that it explains the
phenomena of nature in a very satisfactory manner.
This substance, whatever it is, being the cause of heat, or, in other words, the
sensation which we call warmth being caused by the accumulation of this substance, we
cannot, in strict language, distinguish it by the term heat; because the same name would
then very improperly express both cause and effect. For this reason, in the memoir which
I published in 1777,2 I gave it the names of igneous fluid and matter of heat. And, since
that time, in the work3 published by Mr. de Morveau, Mr. Berthollet, Mr. de Fourcroy,
and myself, upon the reformation of chemical nomenclature, we thought it necessary to
banish all periphrastic expressions, which both lengthen physical language, and render it
more tedious and less distinct, and which even frequently does not convey sufficiently
just ideas of the subject intended. Wherefore, we have distinguished the cause of heat, or
that exquisitely elastic fluid which produces it, by the term of caloric. Besides, that this
expression fulfils our object in the system which we have adopted, it possesses this
farther advantage, that it accords with every species of opinion, since, strictly speaking,
we are not obliged to suppose this to be a real substance; it being sufficient, as will more
clearly appear in the sequel of this work, that it be considered as the repulsive cause,
whatever that may be, which separates the particles of matter from each other; so that we
are still at liberty to investigate its effects in an abstract and mathematical manner.
In the present state of our knowledge, we are unable to determine whether light be
a modification of caloric, or if caloric be, on the contrary, a modification of light. This,
1 Whenever the degree of heat occurs in this work, it is stated by the author according to Reaumur's scale.
The degrees within brackets are the correspondent degrees of Fahrenheit's scale, added by the translator. —
Translator.
2 Collections of the French Academy of Sciences for that year, p. 420.
3 Chemical Nomenclature.
77
however, is indisputable, that, in a system where only decided facts are admissible, and
where we avoid, as far as possible, to suppose anything to be that is not really known to
exist, we ought provisionally to distinguish, by distinct terms, such things as are known
to produce different effects. We therefore distinguish light from caloric; though we do not
therefore deny that these have certain qualities in common, and that, in certain
circumstances, they combine with other bodies almost in the same manner, and produce,
in part, the same effects.
What I have already said may suffice to determine the idea affixed to the
word caloric; but there remains a more difficult attempt, which is to give a just
conception of the manner in which caloric acts upon other bodies. Since this subtle matter
penetrates through the pores of all known substances; since there are no vessels through
which it cannot escape, and, consequently, as there are none which are capable of
retaining it, we can only come at the knowledge of its properties by effects which are
fleeting, and difficultly ascertainable. It is in these things which we neither see nor feel,
that it is especially necessary to guard against the extravagancy of our imagination, which
forever inclines to step beyond the bounds of truth, and is very difficultly restrained
within the narrow line of facts.
We have already seen, that the same body becomes solid, or fluid, or aeriform,
according to the quantity of caloric by which it is penetrated; or, to speak more strictly,
according as the repulsive force exerted by the caloric is equal to, stronger, or weaker,
than the attraction of the particles of the body it acts upon.
But, if these two powers only existed, bodies would become liquid at an
indivisible degree of the thermometer, and would almost instantaneously pass from the
solid state of aggregation to that of aeriform elasticity. Thus water, for instance, at the
very moment when it ceases to be ice, would begin to boil, and would be transformed
into an aeriform fluid, having its particles scattered indefinitely through the surrounding
space. That this does not happen must depend upon the action of some third power. The
pressure of the atmosphere prevents this separation, and causes the water to remain in the
liquid state till it be raised to a temperature of 80° (212°) above zero of the French
thermometer, the quantity of caloric which it receives in the lowest temperature being
insufficient to overcome the pressure of the atmosphere.
Whence it appears that, without this atmospheric pressure, we should not have
any permanent liquid, and should only be able to see bodies in that state of existence in
the very instant of melting, as the smallest additional caloric would instantly separate
their particles, and dissipate them through the surrounding medium. Besides, without this
atmospheric pressure, we should not even have any aeriform fluids, strictly speaking,
because the moment the force of attraction is overcome by the repulsive power of the
caloric, the particles would separate themselves indefinitely, having nothing to give limits
to their expansion, unless their own gravity might collect them together, so as to form an
atmosphere.
Simple reflection upon the most common experiments is sufficient to evince the
truth of these positions. They are more particularly proved by the following experiment,
which I published in the Memoirs of the French Academy for 1777, p. 426.
78
Having filled with sulfuric ether4 a small
narrow glass vessel, A, (Fig. 17.), standing upon
its stalk P, the vessel, which is from twelve to
fifteen lines diameter, is to be covered by a wet
bladder, tied round its neck with several turns of
strong thread; for greater security, fix a second
bladder over the first. The vessel should be filled
in such a manner with the ether, as not to leave
the smallest portion of air between the liquor and
the bladder. It is now to be placed under the
recipient BCD of an air-pump, of which the
upper part B ought to be fitted with a leathern
lid, through which passes a wire EF, having its
point F very sharp; and in the same receiver
there ought to be placed the barometer GH. The
whole being thus disposed, let the recipient be
exhausted, and then, by pushing down the wire
EF, we make a hole in the bladder. Immediately
the ether begins to boil with great violence, and
is changed into an elastic aeriform fluid, which
fills the receiver. If the quantity of ether be
sufficient to leave a few drops in the phial after the evaporation is finished, the elastic
fluid produced will sustain the mercury in the barometer attached to the air-pump, at
eight or ten inches in winter, and from twenty to twenty-five in summer. To render this
experiment more complete, we may introduce a small thermometer into the phial A,
containing the ether, which will descend considerably during the evaporation.
The only effect produced in this experiment is the taking away the weight of the
atmosphere, which, in its ordinary state, presses on the surface of the ether; and the
effects resulting from this removal evidently prove that, in the ordinary temperature of
the earth, ether would always exist in an aeriform state, but for the pressure of the
atmosphere, and that the passing of the ether from the liquid to the aeriform state is
accompanied by a considerable lessening of heat; because, during the evaporation, a part
of the caloric, which was before in a free state, or at least in equilibrium in the
surrounding bodies, combines with the ether, and causes it to assume the aeriform state.
The same experiment succeeds with all evaporable fluids, such as alcohol, water,
and even mercury; with this difference, that the atmosphere formed in the receiver by
alcohol only supports the attached barometer about one inch in winter, and about four or
five inches in summer; that formed by water, in the same situation, raises the mercury
only a few lines, and that by quicksilver but a few fractions of a line. There is therefore
less fluid evaporated from alcohol than from ether, less from water than from alcohol,
and still less from mercury than from either; consequently there is less caloric employed,
and less cold produced, which quadrates exactly with the results of these experiments.
4 As I shall afterwards give a definition, and explain the properties of the liquor called ether, I shall only
premise here, that it is a very volatile inflammable liquor, having a considerably smaller specific gravity
than water, or even spirit of wine.—Author.
79
Another species of experiment proves very evidently that the aeriform state is a
modification of bodies dependent on the degree of temperature, and on the pressure
which these bodies undergo. In a Memoir read by Mr. de la Place and me to the Academy
in 1777, which has not been printed, we have shown that when ether is subjected to a
pressure equal to twenty-eight inches of the barometer, or about the medium pressure of
the atmosphere, it boils at the temperature of about 32° (104°), or 33° (106.25°), of the
thermometer. Mr. de Luc, who has made similar experiments with spirit of wine, finds it
boils at 67° (182.75°). And all the world knows that water boils at 80° (212°). Now,
boiling being only the evaporation of a liquid, or the moment of its passing from the fluid
to the aeriform state, it is evident that, if we keep ether continually at the temperature of
33° (106.25°), and under the common pressure of the atmosphere, we shall have it always
in an elastic aeriform state; and that the same thing will happen with alcohol when above
67° (182.75°), and with water when above 80° (212°); all which are perfectly
conformable to the following experiment.5
I filled a large vessel ABCD (Fig. 15.) with
water, at 35° (110.75°), or 36° (113°); I suppose the
vessel transparent, that we may see what takes place in
the experiment; and we can easily hold the hands in
water at that temperature without inconvenience. Into
it I plunged some narrow necked bottles F, G, which
were filled with the water, after which they were
turned up, so as to rest on their mouths on the bottom
of the vessel. Having next put some ether into a very
small matrass, with its neck a b c, twice bent as in the
figure, I plunged this matrass into the water, so as to
have its neck inserted into the mouth of one of the bottles F. Immediately upon feeling
the effects of the heat communicated to it by the water in the vessel ABCD it began to
boil; and the caloric entering into combination with it, changed it into elastic aeriform
fluid, with which I filled several bottles successively, F, G, &c.
This is not the place to enter upon the examination of the nature and properties of
this aeriform fluid, which is extremely inflammable; but, confining myself to the object at
present in view, without anticipating circumstances, which I am not to suppose the reader
to know, I shall only observe that the ether, from this experiment, is almost only capable
of existing in the aeriform state in our world; for, if the weight of our atmosphere was
only equal to between 20 and 24 inches of the barometer, instead of 28 inches, we should
never be able to obtain ether in the liquid state, at least in summer; and the formation of
ether would consequently be impossible upon mountains of a moderate degree of
elevation, as it would be converted into gas immediately upon being produced, unless we
employed recipients of extraordinary strength, together with refrigeration and
compression. And, lastly, the temperature of the blood being nearly that at which ether
passes from the liquid to the aeriform state, it must evaporate in the primae viae, and
consequently it is very probable the medical properties of this fluid depend chiefly upon
its mechanical effect.
5 See Memoirs of the French Academy, 1780, p. 335.—Author.
80
These experiments succeed better with nitrous ether, because it evaporates in a
lower temperature than sulfuric ether. It is more difficult to obtain alcohol in the aeriform
state; because, as it requires 67° (182.75°) to reduce it to vapor, the water of the bath
must be almost boiling, and consequently it is impossible to plunge the hands into it at
that temperature.
It is evident that if water were used in the foregoing
experiment, it would be changed into gas when exposed to a
temperature superior to that at which it boils. Although
thoroughly convinced of this, Mr. de la Place and myself judged
it necessary to confirm it by the following direct experiment.
We filled a glass jar A, (Fig. 5.) with mercury, and placed it
with its mouth downwards in a dish B, likewise filled with
mercury, and having introduced about two gross of water into
the jar, which rose to the top of the mercury at CD; we then
plunged the whole apparatus into an iron boiler EFGH, full of
boiling sea-water of the temperature of 85° (223.25°), placed
upon the furnace GHIK. Immediately upon the water over the
mercury attaining the temperature of 80° (212°), it began to boil;
and, instead of only filling the small space ACD, it was
converted into an aeriform fluid, which filled the whole jar; the
mercury even descended below the surface of that in the dish B;
and the jar must have been overturned, if it had not been very
thick and heavy, and fixed to the dish by means of iron-wire.
Immediately after withdrawing the apparatus from the boiler,
the vapor in the jar began to condense, and the mercury rose to
its former station; but it returned again to the aeriform state a
few seconds after replacing the apparatus in the boiler.
We have thus a certain number of substances, which are
convertible into elastic aeriform fluids by degrees of
temperature, not much superior to that of our atmosphere. We
shall afterwards find that there are several others which undergo
the same change in similar circumstances, such as muriatic or marine acid, ammoniac or
volatile alkali, the carbonic acid or fixed air, the sulfurous acid, &c. All of these are
permanently elastic in or about the mean temperature of the atmosphere, and under its
common pressure.
All these facts, which could be easily multiplied if necessary, give me full right to
assume, as a general principle, that almost every body in nature is susceptible of three
several states of existence, solid, liquid, and aeriform, and that these three states of
existence depend upon the quantity of caloric combined with the body. Henceforwards I
shall express these elastic aeriform fluids by the generic term gas; and in each species of
gas I shall distinguish between the caloric, which in some measure serves the purpose of
a solvent, and the substance, which in combination with the caloric forms the base of the
gas.
To these bases of the different gases, which are hitherto but little known, we have
been obliged to assign names; these I shall point out in Chap. IV of this work, when I
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have previously given an account of the phenomena attendant upon the heating and
cooling of bodies, and when I have established precise ideas concerning the composition
of our atmosphere.
We have already shown that the particles of every substance in nature exist in a
certain state of equilibrium, between that attraction which tends to unite and keep the
particles together, and the effects of the caloric which tends to separate them. Hence the
caloric not only surrounds the particles of all bodies on every side, but fills up every
interval which the particles of bodies leave between each other. We may form an idea of
this, by supposing a vessel filled with small spherical leaden bullets, into which a
quantity of fine sand is poured, which, insinuating into the intervals between the bullets,
will fill up every void. The balls, in this comparison, are to the sand which surrounds
them exactly in the same situation as the particles of bodies are with respect to the
caloric; with this difference only, that the balls are supposed to touch each other, whereas
the particles of bodies are not in contact, being retained at a small distance from each
other, by the caloric.
If, instead of spherical balls, we substitute solid bodies of a hexahedral,
octohedral, or any other regular figure, the capacity of the intervals between them will be
lessened, and consequently will no longer contain the same quantity of sand. The same
thing takes place, with respect to natural bodies; the intervals left between their particles
are not of equal capacity, but vary in consequence of the different figures and magnitude
of their particles, and of the distance at which these particles are maintained, according to
the existing proportion between their inherent attraction, and the repulsive force exerted
upon them by the caloric.
In this manner we must understand the following expression, introduced by the
English philosophers, who have given us the first precise ideas upon this subject; the
capacity of bodies for containing the matter of heat. As comparisons with sensible
objects are of great use in assisting us to form distinct notions of abstract ideas, we shall
endeavor to illustrate this, by instancing the phenomena which take place between water
and bodies which are wetted and penetrated by it, with a few reflections.
If we immerse equal pieces of different kinds of wood, suppose cubes of one foot
each, into water, the fluid gradually insinuates itself into their pores, and the pieces of
wood are augmented both in weight and magnitude: But each species of wood will
imbibe a different quantity of water; the lighter and more porous woods will admit a
larger, the compact and closer grained will admit of a lesser quantity; for the proportional
quantities of water imbibed by the pieces will depend upon the nature of the constituent
particles of the wood, and upon the greater or lesser affinity subsisting between them and
water. Very resinous wood, for instance, though it may be at the same time very porous,
will admit but little water. We may therefore say that the different kinds of wood possess
different capacities for receiving water; we may even determine, by means of the
augmentation of their weights, what quantity of water they have actually absorbed; but,
as we are ignorant how much water they contained, previous to immersion, we cannot
determine the absolute quantity they contain, after being taken out of the water.
The same circumstances undoubtedly take place, with bodies that are immersed in
caloric; taking into consideration, however, that water is an incompressible fluid, whereas
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caloric is, on the contrary, endowed with very great elasticity; or, in other words, the
particles of caloric have a great tendency to separate from each other, when forced by any
other power to approach; this difference must of necessity occasion very considerable
diversities in the results of experiments made upon these two substances.
Having established these clear and simple propositions, it will be very easy to
explain the ideas which ought to be affixed to the following expressions, which are by no
means synonymous, but possess each a strict and determinate meaning, as in the
following definitions:
Free caloric is that which is not combined in any manner with any other body.
But, as we live in a system to which caloric has a very strong adhesion, it follows that we
are never able to obtain it in the state of absolute freedom.
Combined caloric is that which is fixed in bodies by affinity or elective attraction,
so as to form part of the substance of the body, even part of its solidity.
By the expression specific caloric of bodies we understand the respective
quantities of caloric requisite for raising a number of bodies of the same weight to an
equal degree of temperature. This proportional quantity of caloric depends upon the
distance between the constituent particles of bodies, and their greater or lesser degrees of
cohesion; and this distance, or rather the space or void resulting from it, is, as I have
already observed, called the capacity of bodies for containing caloric.
Heat, considered as a sensation, or, in other words, sensible heat, is only the effect
produced upon our sentient organs, by the motion or passage of caloric, disengaged from
the surrounding bodies. In general, we receive impressions only in consequence of
motion, and we might establish it as an axiom, That without motion there is no sensation.
This general principle applies very accurately to the sensations of heat and cold: When
we touch a cold body, the caloric which always tends to become in equilibrium in all
bodies, passes from our hand into the body we touch, which gives us the feeling or
sensation of cold. The direct contrary happens, when we touch a warm body, the caloric
then passing from the body into our hand, produces the sensation of heat. If the hand and
the body touched be of the same temperature, or very nearly so, we receive no
impression, either of heat or cold, because there is no motion or passage of caloric; and
thus no sensation can take place, without some correspondent motion to occasion it.
When the thermometer rises, it shows that free caloric is entering into the
surrounding bodies: The thermometer, which is one of these, receives its share in
proportion to its mass, and to the capacity which it possesses for containing caloric. The
change therefore which takes place upon the thermometer, only announces a change of
place of the caloric in those bodies, of which the thermometer forms one part; it only
indicates the portion of caloric received, without being a measure of the whole quantity
disengaged, displaced, or absorbed.
The most simple and most exact method for determining this latter point, is that
described by Mr. de la Place, in the Memoirs of the Academy, 1780, p. 364; a summary
explanation of which will be found towards the conclusion of this work. This method
consists in placing a body, or a combination of bodies, from which caloric is disengaging,
in the midst of a hollow sphere of ice; and the quantity of ice melted becomes an exact
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measure of the quantity of caloric disengaged. It is possible, by means of the apparatus
which we have caused to be constructed upon this plan, to determine, not as has been
pretended, the capacity of bodies for containing heat, but the ratio of the increase or
diminution of capacity produced by determinate degrees of temperature. It is easy with
the same apparatus, by means of diverse combinations of experiments, to determine the
quantity of caloric requisite for converting solid substances into liquids, and liquids into
elastic aeriform fluids; and, vice versa, what quantity of caloric escapes from elastic
vapors in changing to liquids, and what quantity escapes from liquids during their
conversion into solids. Perhaps, when experiments have been made with sufficient
accuracy, we may one day be able to determine the proportional quantity of caloric
necessary for producing the several species of gasses. I shall hereafter, in a separate
chapter, give an account of the principal results of such experiments as have been made
upon this head.
It remains, before finishing this article, to say a few words relative to the cause of
the elasticity of gasses, and of fluids in the state of vapor. It is by no means difficult to
perceive that this elasticity depends upon that of caloric, which seems to be the most
eminently elastic body in nature. Nothing is more readily conceived, than that one body
should become elastic by entering into combination with another body possessed of that
quality. We must allow that this is only an explanation of elasticity, by an assumption of
elasticity, and that we thus only remove the difficulty one step farther, and that the nature
of elasticity, and the reason for caloric being elastic, remains still unexplained. Elasticity
in the abstract is nothing more than that quality of the particles of bodies by which they
recede from each other when forced together. This tendency in the particles of caloric to
separate, takes place even at considerable distances. We shall be satisfied of this, when
we consider that air is susceptible of undergoing great compression, which supposes that
its particles were previously very distant from each other; for the power of approaching
together certainly supposes a previous distance, at least equal to the degree of approach.
Consequently, those particles of the air, which are already considerably distant from each
other, tend to separate still farther. In fact, if we produce Boyle's vacuum in a large
receiver, the very last portion of air which remains spreads itself uniformly through the
whole capacity of the vessel, however large, fills it completely throughout, and presses
everywhere against its sides: We cannot, however, explain this effect, without supposing
that the particles make an effort to separate themselves on every side, and we are quite
ignorant at what distance, or what degree of rarefaction, this effort ceases to act.
Here, therefore, exists a true repulsion between the particles of elastic fluids; at
least, circumstances take place exactly as if such a repulsion actually existed; and we
have very good right to conclude, that the particles of caloric mutually repel each other.
When we are once permitted to suppose this repelling force, the rationale of the
formation of gasses, or aeriform fluids, becomes perfectly simple; though we must, at the
same time, allow, that it is extremely difficult to form an accurate conception of this
repulsive force acting upon very minute particles placed at great distances from each
other.
It is, perhaps, more natural to suppose, that the particles of caloric have a stronger
mutual attraction than those of any other substance, and that these latter particles are
forced asunder in consequence of this superior attraction between the particles of the
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caloric, which forces them between the particles of other bodies, that they may be able to
reunite with each other. We have somewhat analogous to this idea in the phenomena
which occur when a dry sponge is dipped into water: The sponge swells; its particles
separate from each other; and all its intervals are filled up by the water. It is evident, that
the sponge, in the act of swelling, has acquired a greater capacity for containing water
than it had when dry. But we cannot certainly maintain, that the introduction of water
between the particles of the sponge has endowed them with a repulsive power, which
tends to separate them from each other; on the contrary, the whole phenomena are
produced by means of attractive powers; and these are, first, The gravity of the water, and
the power which it exerts on every side, in common with all other fluids; 2dly, The force
of attraction which takes place between the particles of the water, causing them to unite
together; 3dly, The mutual attraction of the particles of the sponge with each
other; and, lastly, The reciprocal attraction which exists between the particles of the
sponge and those of the water. It is easy to understand, that the explanation of this fact
depends upon properly appreciating the intensity of, and connection between, these
several powers. It is probable that the separation of the particles of bodies, occasioned by
caloric, depends in a similar manner upon a certain combination of different attractive
powers, which, in conformity with the imperfection of our knowledge, we endeavor to
express by saying, that caloric communicates a power of repulsion to the particles of
bodies.
CHAPTER II.
General Views relative to the Formation and Composition of our Atmosphere.
These views which I have taken of the formation of elastic aeriform fluids or gasses
throw great light upon the original formation of the atmospheres of the planets, and
particularly that of our earth. We readily conceive, that it must necessarily consist of a
mixture of the following substances: First, Of all bodies that are susceptible of
evaporation, or, more strictly speaking, which are capable of retaining the state of
aeriform elasticity in the temperature of our atmosphere, and under a pressure equal to
that of a column of twenty-eight inches of quicksilver in the barometer; and, secondly, Of
all substances, whether liquid or solid, which are capable of being dissolved by this
mixture of different gasses.
The better to determine our ideas relating to this subject, which has not hitherto
been sufficiently considered, let us, for a moment, conceive what change would take
place in the various substances which compose our earth, if its temperature were
suddenly altered. If, for instance, we were suddenly transported into the region of the
planet Mercury, where probably the common temperature is much superior to that of
boiling water, the water of the earth, and all the other fluids which are susceptible of the
gaseous state, at a temperature near to that of boiling water, even quicksilver itself, would
become rarified; and all these substances would be changed into permanent aeriform
fluids or gasses, which would become part of the new atmosphere. These new species of
airs or gasses would mix with those already existing, and certain reciprocal
decompositions and new combinations would take place, until such time as all the
elective attractions or affinities subsisting amongst all these new and old gaseous
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substances had operated fully; after which, the elementary principles composing these
gasses, being saturated, would remain at rest. We must attend to this, however, that, even
in the above hypothetical situation, certain bounds would occur to the evaporation of
these substances, produced by that very evaporation itself; for as, in proportion to the
increase of elastic fluids, the pressure of the atmosphere would be augmented, as every
degree of pressure tends, in some measure, to prevent evaporation, and as even the most
evaporable fluids can resist the operation of a very high temperature without evaporating,
if prevented by a proportionally stronger compression, water and all other liquids being
able to sustain a red heat in Papin’s digester; we must admit, that the new atmosphere
would at last arrive at such a degree of weight, that the water which had not hitherto
evaporated would cease to boil, and, of consequence, would remain liquid; so that, even
upon this supposition, as in all others of the same nature, the increasing gravity of the
atmosphere would find certain limits which it could not exceed. We might even extend
these reflections greatly farther, and examine what change might be produced in such
situations upon stones, salts, and the greater part of the fusible substances which compose
the mass of our earth. These would be softened, fused, and changed into fluids, &c.: But
these speculations carry me from my object, to which I hasten to return.
By a contrary supposition to the one we have been forming, if the earth were
suddenly transported into a very cold region, the water which at present composes our
seas, rivers, and springs, and probably the greater number of the fluids we are acquainted
with, would be converted into solid mountains and hard rocks, at first diaphanous and
homogeneous, like rock crystal, but which, in time, becoming mixed with foreign and
heterogeneous substances, would become opaque stones of various colors. In this case,
the air, or at least some part of the aeriform fluids which now compose the mass of our
atmosphere, would doubtless lose its elasticity for want of a sufficient temperature to
retain them in that state: They would return to the liquid state of existence, and new
liquids would be formed, of whose properties we cannot, at present, form the most distant
idea.
These two opposite suppositions give a distinct proof of the following
corollaries: First, That solidity, liquidity, and aeriform elasticity, are only three different
states of existence of the same matter, or three particular modifications which almost all
substances are susceptible of assuming successively, and which solely depend upon the
degree of temperature to which they are exposed; or, in other words, upon the quantity of
caloric with which they are penetrated.6 2dly, That it is extremely probable that air is a
fluid naturally existing in a state of vapor; or, as we may better express it, that our
atmosphere is composed of all the fluids which are susceptible of the vaporous or
permanently elastic state, in the usual temperature, and under the common pressure. 3dly,
That it is not impossible we may discover, in our atmosphere, certain substances naturally
very compact, even metals themselves; as a metallic substance, for instance, only a little
more volatile than mercury, might exist in that situation.
Amongst the fluids with which we are acquainted, some, as water and alcohol, are
susceptible of mixing with each other in all proportions; whereas others, on the contrary,
as quicksilver, water, and oil, can only form a momentary union; and, after being mixed
6 The degree of pressure which they undergo must be taken into account.—Translator.
86
together, separate and arrange themselves according to their specific gravities. The same
thing ought to, or at least may, take place in the atmosphere. It is possible, and even
extremely probable, that, both at the first creation, and every day, gasses are formed,
which are difficultly miscible with atmospheric air, and are continually separating from
it. If these gasses be specifically lighter than the general atmospheric mass, they must, of
course, gather in the higher regions, and form strata that float upon the common air. The
phenomena which accompany igneous meteors induce me to believe, that there exists in
the upper parts of our atmosphere a stratum of inflammable fluid in contact with those
strata of air which produce the phenomena of the aurora borealis and other fiery
meteors.—I mean hereafter to pursue this subject in a separate treatise.
Questions and Problems, etc.
1. Distinguish between phlogiston (which Lavoisier rejects) and caloric (which he does not
reject). Is Lavoisier’s acceptance of caloric as an element a violation of his own standard
by which he rejects phlogiston?
2. Though Lavoisier considers caloric as an element, it has a special characteristic (or
characteristics) that seems to separate it (and light) as a special kind of element. What is
special about caloric (and light)?
* * * * *
87
Is Heat a Substance? Two Papers to the Contrary
Sir Humphry Davy
Excerpts from
An Essay on Heat, Light, and the Combinations of Light1
Matter is possessed of the power of attraction. By this power the particles of bodies tend
to approximate, and to exist in a state of contiguity. The particles of all bodies with which
we are acquainted can be made to approach nearer to each other by peculiar means, that
is, the specific gravity of all bodies can be increased by diminishing their temperatures.
Consequently (on the supposition of the impenetrability of matter), the particles of bodies
are not in actual contact. There must then act on the corpuscles of bodies some other
power which prevents their actual contact; this may be called repulsion. The phenomena
of repulsion have been supposed, by the greater part of chemical philosophers, to depend
on a peculiar elastic fluid, to which the names of latent heat2 and caloric have been given.
The peculiar modes of existence of bodies—solidity, fluidity, and gasity— depend
(according to the calorists) on the quantity of the fluid of heat entering into their
composition; this substance insinuating itself between their corpuscles, separating them
from each other, and preventing their actual contact, is by them supposed to be the cause
of repulsion.
Other philosophers, dissatisfied with the evidences produced in favor of the
existence of this fluid, and perceiving the generation of heat by friction and percussion,
have supposed it to be motion.
Considering the discovery of the true cause of the repulsive power as highly
important to philosophy, I have endeavored to investigate this art of chemical science by
experiments: From these experiments (of which I am now about to give a detail) I
conclude that heat, or the power of repulsion, is not matter. . . .
Experiment I
The Phenomena of Repulsion Are Not Dependent on a Peculiar Elastic Fluid for Their
Existence, or Caloric Does not Exist
Without considering the effects of the repulsive power on bodies, or endeavoring to prove
from these effects that it is motion, I shall attempt to demonstrate by experiments that it is
not matter; and in doing this, I shall use the method called by mathematicians reductio ad
absurdum.
Let heat be considered as matter, and let it be granted that the temperature of
bodies cannot be increased unless their [heat] capacities are diminished from some cause,
1 [Contributions to Physical and Medical Knowledge, Principally from the West of England, collected by
Thomas Beddoes, M.D., 1799, taken from William Francis Magie, ed., A Source Book in Physics (New
York: McGraw-Hill, 1935), 161-165].
2 [“Latent heat” is here used in a non-technical sense, meaning only heat that is hidden. Black’s papers on
specific and latent heat were not published until 1803.]
88
or heat added to them from some bodies in contact.
Now the temperatures of bodies are uniformly raised by friction and percussion.
And since an increase of temperature is consequent on friction and percussion, it must
consequently be generated in one of these modes: First, either from a diminution of the
capacities of the acting bodies from some change induced in them by friction, a change
producing in them an increase of temperature.
Secondly, or from heat communicated from the decomposition of the oxygen gas
in contact by one or both of the bodies, and then friction must effect some change in them
(similar to an increase of temperature) enabling them to decompose oxygen gas, and they
must be found after friction partially or wholly oxydated.
Thirdly, or from a communication of caloric from the bodies in contact, produced
by a change induced by friction in the acting bodies, enabling them to attract caloric from
the surrounding bodies.
Now first let the increase of temperature produced by friction and percussion be
supposed to arise from a diminution of the capacities of the acting bodies. In this case it is
evident some change must be induced in the bodies by the action, which [change] lessens
their capacities and increases their temperatures. . . .
Experiment II
I procured two parallelopipedons of ice of the temperature of 29°, six inches long, two
wide, and two-thirds of an inch thick; they were fastened by wires to two bars of iron. By
a peculiar mechanism their surfaces were placed in contact and kept in a continued and
violent friction for some minutes. They were almost entirely converted into water, which
water was collected, and its temperature ascertained to be 35°, after remaining in an
atmosphere of a lower temperature for some minutes. The fusion [i.e., melting] took
place only at the plane of contact of the two pieces of ice, and no bodies were in friction
but ice. From this experiment it is evident that ice by friction is converted into water, and,
according to the supposition, its capacity is diminished; but it is a well-known fact, that
the capacity of water for heat is much greater than that of ice; and ice must have an
absolute quantity of heat added to it before it can be converted into water. Friction
consequently does not diminish the capacities of bodies for heat.
From this experiment it is likewise evident that the increase of temperature
consequent on friction cannot arise from the decomposition of the oxygen gas in contact,
for ice has no attraction for oxygen. Since the increase of temperature consequent on
friction cannot arise from the diminution of capacity or oxydation of the acting bodies,
the only remaining supposition is that it arises from an absolute quantity of heat added to
them, which heat must be attracted from the bodies in contact. Then friction must induce
some change in bodies, enabling them to attract heat from the bodies in contact.
89
Experiment III
I procured a piece of clock-work so constructed as to be set to work in the exhausted
receiver;3 one of the external wheels of this machine came in contact with a thin metallic
plate. A considerable degree of sensible heat was produced by friction between the wheel
and plate when the machine worked uninsulated from bodies capable of communicating
heat. I next procured a small piece of ice; round the superior edge of this a small canal
was made and filled with water. The machine was placed on the ice, but not in contact
with the water. Thus disposed, the whole was placed under the receiver (which had been
previously filled with carbonic acid), a quantity of potash (i.e., caustic vegetable alkali)
being at the same time introduced.
The receiver was now exhausted. From the exhaustion, and from the attraction of
the carbonic acid gas by the potash, a vacuum nearly perfect was, I believe, made.
The machine was now set to work. The wax rapidly melting proved the increase
of temperature.4
Caloric then was collected by friction; which caloric, on the supposition, was
communicated by the bodies in contact with the machine. In this experiment, ice was the
only body in contact with the machine. Had this ice given out caloric, the water on the
top of it must have been frozen. The water on the top of it was not frozen; consequently
the ice did not give out caloric. The caloric could not come from the bodies in contact
with the ice; for it must have passed through the ice to penetrate the machine, and an
addition of caloric to the ice would have converted it into water.
Heat, when produced by friction, cannot be collected from the bodies in contact,
and it was proved by the second experiment that the increase of temperature consequent
on friction cannot arise from diminution of capacity or from oxydation. But if it be
considered as matter, it must be produced in one of these modes. Since (as is
demonstrated by these experiments) it is produced in neither of these modes, it cannot be
considered as matter. It has then been experimentally demonstrated that caloric, or the
matter of heat, does not exist.
Solids, by long and violent friction, become expanded and, if of a higher
temperature than our bodies, affect the sensory organs with the peculiar sensation known
by the common name of heat.
Since bodies become expanded by friction, it is evident that their corpuscles must
move or separate from each other. Now a motion or vibration of the corpuscles of bodies
must be necessarily generated by friction and percussion. Therefore we may reasonably
conclude that this motion or vibration is heat, or the repulsive power.
Heat, then, or that power which prevents the actual contact of the corpuscles of
bodies, and which is the cause of our peculiar sensations of heat and cold, may be defined
as a peculiar motion, probably a vibration, of the corpuscles of bodies, tending to separate
them. It may with propriety be called the repulsive motion.
3 [That is, a sealed receptacle that can be evacuated of air, probably with a vacuum pump. This evacuation
is executed on the following page.]
4 [Evidently Davy failed to mention that there is also a piece of wax somewhere within the receiver.]
90
Benjamin Thompson (Count Rumford)
Excerpt from Heat is a Form of Motion: An Experiment in Boring Cannon1
It frequently happens that in the ordinary affairs and occupations of life opportunities
present themselves of contemplation of some of the most curious operations of nature;
and very interesting philosophical experiments might often be made, almost without
trouble or expense, by means of machinery contrived for the mere mechanical purposes
of the arts and manufactures. . . .
Being engaged lately in superintending the boring of cannon in the workshops of
the military arsenal at Munich, I was struck with the very considerable degree of heat
which a brass gun acquires, in a short time, in being bored; and with the still more intense
heat (much greater than that of boiling water, as I found by experiment) of the metallic
chips separated from it by the borer.
The more I meditated on these phenomena, the more they appeared to me to be
curious and interesting. A thorough investigating of them seemed even to bid fair to give
a farther insight into the hidden nature of heat, and to enable us to form some reasonable
conjectures respecting the existence, or non-existence, of an igneous fluid—a subject on
which the opinions of philosophers have, in all ages, been much divided.
In order that the [Royal] Society may have clear and distinct ideas of the
speculations and also of the specific objects of philosophical investigation they suggested
to me, I must beg leave to state them at some length and in such manner as I shall think
best to answer this purpose.
From whence comes the heat actually produced in the mechanical operation
above mentioned? Is it furnished by the metallic chips which are separated by the borer
from the solid mass of metal? If this were the case, then, according to the modern
doctrines of latent heat and of caloric, the capacity for the heat of the parts of the metal,
so reduced to chips, ought not only to be changed, but the change undergone by them
should be sufficiently great to account for all the heat produced.
But no such change had taken place; for I found, upon taking equal quantities, by
weight, of these chips, and of thin slips of the same block of metal separated by means of
a fine saw, and putting them at the same temperature (that of boiling water) into equal
quantities of cold water (that is to say, at the temperature of 59½ °F), the portion of the
water into which the chips were put was not, to all appearance, heated either less or more
than the other portion in which the slips of metal were to put.
This experiment being repeated several times, the results were always so nearly
the same that I could not determine whether any or what change had been produced in the
metal, in regard to its capacity for heat, by being reduced to chips by the borer.
From hence it is evident that the heat produced could not possibly have been
furnished at the expense of the latent heat of the metallic chips. . . .
By meditating on the results of all these experiments, we are naturally brought to
that great question which has so often been the subject of speculation among
philosophers; namely:
What is heat? Is there any such thing as an igneous fluid? Is there anything that
1 [Philosophical Transactions (vol. 88), 1798, from William Francis Magie, ed., A Source Book in Physics,
151-152, 160-161].
91
can with propriety be called caloric?
We have seen that a very considerable quantity of heat may be excited in the
friction of two metallic surfaces and given off in a constant stream or flux, in all
directions, without iteration or intermission, and without any signs of diminution or
exhaustion.
From whence came the heat which was continually given off in this manner in the
foregoing experiments? Was it furnished by the small particles of metal, detached from
the larger solid masses, on their being rubbed together? This, as we have already seen,
could not possibly have been the case.
Was it furnished by the air? This could not have been the case; for in three of the
experiments, the machinery being kept immersed in water, the access of the air of the
atmosphere was completely prevented.
Was it furnished by the water which surrounded the machinery? That this could
not have been the case is evident: first, because this water was continually receiving heat
from the machinery and could not, at the same time, be giving to, and receiving heat
from, the same body; and secondly, because there was no chemical decomposition of any
part of this water. Had any such decomposition taken place (which indeed could not
reasonably have been expected), one of its component elastic fluids (most probably
inflammable air) must, at the same time, have been set at liberty, and in making its escape
into the atmosphere would have been detected; but though I frequently examined the
water to see if any air bubbles rose up through it, and had even made preparations for
catching them in order to examine them if any should appear, I could perceive none; nor
was there any sign of decomposition of any kind whatever, or other chemical process,
going on in the water.
Is it possible that the heat could have been supplied by means of the iron bar to
the end of which the blunt steel borer was fixed? Or by the small neck of gun metal by
which the hollow cylinder was united to the cannon? These suppositions appear more
improbable even than either of these before mentioned; for heat was continually going
off, or out of the machinery, by both these passages, during the whole time the
experiment lasted.
And, in reasoning on this subject, we must not forget to consider that most
remarkable circumstance: that the source of the heat generated by friction in these
experiments appeared evidently to be inexhaustible.
It is indeed hardly necessary to add that anything which any insulated body, or
system of bodies, can continue to furnish without limitation cannot possibly be a material
substance, and it appears to me to be extremely difficult, if not quite impossible, to form
any distinct idea of anything capable of being excited and communicated in the manner
the heat was excited and communicated in these, except it be MOTION.2
2 [Despite the publication of these papers, the notion that heat is a substance endured for more than half a
century after, so you will see it in many of the authors we’ll be reading in the next few months. Black, for
one, argued that if heat is a motion, then one would then expect the densest bodies to have the greatest heat
capacities—the idea being that a denser body would have particles that would be harder to get moving—
whereas the reverse is often the case. Nevertheless, the position of Davy and Rumford has been accepted by
modern science since the mid-to-late nineteenth century.]
92
Lavoisier
Elements of Chemistry
PART I
CHAPTER VIII
Of the Radical Principle of Water, and of its Decomposition by Charcoal and Iron.
Until very lately, water has always been thought a simple substance, insomuch that the
older chemists considered it as an element. Such it undoubtedly was to them, as they
were unable to decompose it; or, at least, since the decomposition which took place daily
before their eyes was entirely unnoticed. But we mean to prove that water is by no means
a simple or elementary substance. I shall not here pretend to give the history of this recent
and hitherto contested discovery, which is detailed in the Memoirs of the Academy for
1781, but shall only bring forward the principal proofs of the decomposition and
composition of water; and I may venture to say that these will be convincing to such as
consider them impartially.
Experiment First.
Having fixed the glass tube EF (Fig. 11.), of from 8 to 12 lines diameter, across a
furnace, with a small inclination from E to F, sealed the superior extremity E to the glass
retort A, containing a determinate quantity of distilled water, and to the inferior extremity
F, the worm SS fixed into the neck of the doubly tubulated bottle H, which has the bent
tube KK adapted to one of its openings, in such a manner as to convey such aeriform
fluids or gasses as may be disengaged, during the experiment, into a proper apparatus for
determining their quantity and nature.
To render the success of this experiment certain, it is necessary that the tube EF
be made of well annealed and difficultly fusible glass, and that it be coated with a lute
composed of clay mixed with powdered stone-ware; besides which, it must be supported
about its middle by means of an iron bar passed through the furnace, lest it should soften
93
and bend during the experiment. A tube of China-ware, or porcelain, would answer better
than one of glass for this experiment, were it not difficult to procure one so entirely free
from pores as to prevent the passage of air or of vapors.
When things are thus arranged, a fire is lighted in the furnace EFCD, which is
supported of such a strength as to keep the tube EF red hot, but not to make it melt; and,
at the same time, such a fire is kept up in the furnace VVXX, as to keep the water in the
retort A continually boiling.
In proportion as the water in the retort A is evaporated, it fills the tube EF and
drives out the air it contained by the tube KK; the aqueous gas formed by evaporation is
condensed by cooling in the worm SS, and falls, drop by drop, into the tubed bottle H.
Having continued this operation until all the water be evaporated from the retort, and
having carefully emptied all the vessels employed, we find that a quantity of water has
passed over into the bottle H, exactly equal to what was before contained in the retort A,
without any disengagement of gas whatsoever: So that this experiment turns out to be a
simple distillation; and the result would have been exactly the same, if the water had been
run from one vessel into the other, through the tube EF, without having undergone the
intermediate incandescence.
Experiment Second.
The apparatus being disposed, as in the former experiment, 28 grs. of charcoal,
broken into moderately small parts, and which has previously been exposed for a long
time to a red heat in close vessels, are introduced into the tube EF. Everything else is
managed as in the preceding experiment.
The water contained in the retort A is distilled, as in the former experiment, and,
being condensed in the worm, falls into the bottle H; but, at the same time, a considerable
quantity of gas is disengaged, which, escaping by the tube KK, is received in a
convenient apparatus for that purpose. After the operation is finished, we find nothing but
a few atoms of ashes remaining in the tube EF; the 28 grs. of charcoal having entirely
disappeared.
When the disengaged gasses are carefully examined, they are found to weigh
113.7 grs.1; these are of two kinds, viz. 144 cubical inches of carbonic acid gas, weighing
100 grs. and 380 cubical inches of a very light gas, weighing only 13.7 grs. which takes
fire when in contact with air, by the approach of a lighted body; and, when the water
which has passed over into the bottle H is carefully examined, it is found to have lost
85.7 grs. of its weight. Thus, in this experiment, 85.7 grs. of water, joined to 28 grs. of
charcoal, have combined in such a way as to form 100 grs. of carbonic acid, and
13.7 grs. of a particular gas capable of being burnt.
I have already shown that 100 grs. of carbonic acid gas consists of 72 grs. of
oxygen, combined with 28 grs. of charcoal; hence the 28 grs. of charcoal placed in the
glass tube have acquired 72 grs. of oxygen from the water; and it follows that 85.7 grs. of
water are composed of 72 grs. of oxygen, combined with 13.7 grs. of a gas susceptible of
1 In the latter part of this work will be found a particular account of the processes necessary for separating
the different kinds of gasses, and for determining their quantities.—Author.
94
combustion. We shall see presently that this gas cannot possibly have been disengaged
from the charcoal, and must, consequently, have been produced from the water.
I have suppressed some circumstances in the above account of this experiment,
which would only have complicated and obscured its results in the mind of the reader.
For instance, the inflammable gas dissolves a very small part of the charcoal, by which
means its weight is somewhat augmented, and that of the carbonic gas proportionally
diminished. Although the alteration produced by this circumstance is very inconsiderable,
yet I have thought it necessary to determine its effects by rigid calculation, and to report,
as above, the results of the experiment in its simplified state, as if this circumstance had
not happened. At any rate, should any doubts remain respecting the consequences I have
drawn from this experiment, they will be fully dissipated by the following experiments,
which I am going to adduce in support of my opinion.
Experiment Third.
The apparatus being disposed exactly as in the former experiment, with this
difference, that instead of the 28 grs. of charcoal, the tube EF is filled with 274 grs. of
soft iron in thin plates, rolled up spirally. The tube is made red hot by means of its
furnace, and the water in the retort A is kept constantly boiling till it be all evaporated,
and has passed through the tube EF, so as to be condensed in the bottle H.
No carbonic acid gas is disengaged in this experiment, instead of which we obtain
416 cubical inches, or 15 grs. of inflammable gas, thirteen times lighter than atmospheric
air. By examining the water which has been distilled, it is found to have lost 100 grs. and
the 274 grs. of iron confined in the tube are found to have acquired 85 grs. additional
weight, and its magnitude is considerably augmented. The iron is now hardly at all
attractable by the magnet; it dissolves in acids without effervescence; and, in short, it is
converted into a black oxide, precisely similar to that which has been burnt in oxygen
gas.
In this experiment we have a true oxidation of iron, by means of water, exactly
similar to that produced in air by the assistance of heat. One hundred grains of water
having been decomposed, 85 grs. of oxygen have combined with the iron, so as to
convert it into the state of black oxide, and 15 grs. of a peculiar inflammable gas are
disengaged: From all this it clearly follows, that water is composed of oxygen combined
with the base of an inflammable gas, in the respective proportions of 85 parts, by weight
of the former, to 15 parts of the latter.
Thus water, besides the oxygen, which is one of its elements in common with
many other substances, contains another element as its constituent base or radical, and for
which we must find an appropriate term. None that we could think of seemed better
adapted than the word hydrogen, which signifies the generative principle of water, from
υδορ (aqua), and γεινομας (gignor).2 We call the combination of this element with
2 This expression Hydrogen has been very severely criticized by some, who pretend that it signifies
engendered by water, and not that which engenders water. The experiments related in this chapter prove,
that, when water is decomposed, hydrogen is produced, and that, when hydrogen is combined with oxygen,
water is produced: So that we may say, with equal truth, that water is produced from hydrogen, or hydrogen
is produced from water.—Author.
95
caloric hydrogen gas; and the term hydrogen expresses the base of that gas, or the radical
of water.
This experiment furnishes us with a new combustible body, or, in other words, a
body which has so much affinity with oxygen as to draw it from its connection with
caloric, and to decompose air or oxygen gas. This combustible body has itself so great
affinity with caloric, that, unless when engaged in a combination with some other body, it
always subsists in the aeriform or gaseous state, in the usual temperature and pressure of
our atmosphere. In this state of gas it is about 1/13 of the weight of an equal bulk of
atmospheric air; it is not absorbed by water, though it is capable of holding a small
quantity of that fluid in solution, and it is incapable of being used for respiration.
As the property this gas possesses, in common with all other combustible bodies,
is nothing more than the power of decomposing air, and carrying off its oxygen from the
caloric with which it was combined, it is easily understood that it cannot burn, unless in
contact with air or oxygen gas. Hence, when we set fire to a bottle full of this gas, it burns
gently, first at the neck of the bottle, and then in the inside of it, in proportion as the
external air gets in: This combustion is slow and successive, and only takes place at the
surface of contact between the two gasses. It is quite different when the two gasses are
mixed before they are set on fire: If, for instance, after having introduced one part of
oxygen gas into a narrow-mouthed bottle, we fill it up with two parts of hydrogen gas,
and bring a lighted taper, or other burning body, to the mouth of the bottle, the
combustion of the two gasses takes place instantaneously with a violent explosion. This
experiment ought only to be made in a bottle of very strong green glass, holding not more
than a pint, and wrapped round with twine, otherwise the operator will be exposed to
great danger from the rupture of the bottle, of which the fragments will be thrown about
with great force.
If all that has been related above, concerning the decomposition of water, be
exactly conformable to truth;—if, as I have endeavored to prove, that substance be really
composed of hydrogen, as its proper constituent element, combined with oxygen, it ought
to follow, that, by reuniting these two elements together, we should recompose water; and
that this actually happens may be judged of by the following experiment.
Experiment Fourth.
I took a large crystal balloon A (Fig. 5) holding about 30 pints, having a large
opening to which was cemented the plate of copper BC, pierced with four holes in which
four tubes terminate. The first tube, H h, is intended to be adapted to an air pump, by
which the balloon is to be exhausted of its air. The second tube gg, communicates, by its
extremity MM, with a reservoir of oxygen gas, with which the balloon is to be filled. The
third tube d D d', communicates, by its extremity d NN, with a reservoir of hydrogen gas.
The extremity d' of this tube terminates in a capillary opening, through which the
hydrogen gas contained in the reservoir is forced, with a moderate degree of quickness,
by the pressure of one or two inches of water. The fourth tube contains a metallic wire
FL, having a knob at its extremity L, intended for giving an electrical spark from L to d',
on purpose to set fire to the hydrogen gas: This wire is moveable in the tube, that we may
be able to separate the knob L from the extremity d' of the tube D d'. The three tubes d D
d', gg, and H h, are all provided with stopcocks.
96
That the hydrogen gas
and oxygen gas may be as
much as possible deprived of
water, they are made to pass,
in their way to the balloon A,
through the tubes MM, NN,
of about an inch diameter, and
filled with salts, which, from
their deliquescent nature,
greedily attract the moisture
of the air: Such are the acetate
of potash, and the muriate or
nitrate of lime.3 These
salts must only be reduced to
a coarse powder, lest they run
into lumps, and prevent the
gasses from getting through
their interstices.
We must be provided beforehand with a sufficient quantity of oxygen gas,
carefully purified from all admixture of carbonic acid, by long contact with a solution of
potash.4
We must likewise have a double quantity of hydrogen gas, carefully purified in
the same manner by long contact with a solution of potash in water. The best way of
obtaining this gas free from mixture is by decomposing water with very pure soft iron, as
directed in Exp. 3. of this chapter.
Having adjusted everything properly, as above directed, the tube H h is adapted to
an air-pump, and the balloon A is exhausted of its air. We next admit the oxygen gas so
as to fill the balloon, and then, by means of pressure, as is before mentioned, force a
small stream of hydrogen gas through its tube D d', which we immediately set on fire by
an electric spark. By means of the above described apparatus, we can continue the mutual
combustion of these two gasses for a long time, as we have the power of supplying them
to the balloon from their reservoirs, in proportion as they are consumed. I have in another
place5 given a description of the apparatus used in this experiment, and have explained
the manner of ascertaining the quantities of the gasses consumed with the most
scrupulous exactitude.
In proportion to the advancement of the combustion, there is a deposition of water
upon the inner surface of the balloon or matrass A: The water gradually increases in
3 See the nature of these salts in the second part of this book.—Author.
4 By potash is here meant, pure or caustic alkali, deprived of carbonic acid by means of quick-lime: In
general, we may observe here, that all the alkalis and earths must invariably be considered as in their pure
or caustic state, unless otherwise expressed.—Translator. The method of obtaining this pure alkali of potash
will be given in the sequel.—Author.
5 See the third part of this work.—Author.
97
quantity, and, gathering into large drops, runs down to the bottom of the vessel. It is easy
to ascertain the quantity of water collected, by weighing the balloon both before and after
the experiment. Thus we have a twofold verification of our experiment, by ascertaining
both the quantities of the gasses employed and of the water formed by their combustion:
These two quantities must be equal to each other. By an operation of this kind, Mr.
Meusnier and I ascertained that it required 85 parts, by weight, of oxygen, united to 15
parts of hydrogen, to compose 100 parts of water. This experiment, which has not
hitherto been published, was made in the presence of a numerous committee from the
Royal Academy. We exerted the most scrupulous attention to its accuracy, and have
reason to believe that the above propositions cannot vary a two hundredth part from
absolute truth.
From these experiments, both analytical and synthetic, we may now affirm that
we have ascertained, with as much certainty as is possible in physical or chemical
subjects, that water is not a simple elementary substance, but is composed of two
elements, oxygen and hydrogen; which elements, when existing separately, have so
strong affinity for caloric, as only to subsist under the form of gas in the common
temperature and pressure of our atmosphere.
This decomposition and recomposition of water is perpetually operating before
our eyes, in the temperature of the atmosphere, by means of compound elective
attraction. We shall presently see that the phenomena attendant upon vinous
fermentation, putrefaction, and even vegetation, are produced, at least in a certain degree,
by decomposition of water. It is very extraordinary that this fact should have hitherto
been overlooked by natural philosophers and chemists: Indeed, it strongly proves that in
chemistry, as in moral philosophy, it is extremely difficult to overcome prejudices
imbibed in early education, and to search for truth in any other road than the one we have
been accustomed to follow.
I shall finish this chapter by an experiment much less demonstrative than those
already related, but which has appeared to make more impression than any other upon the
minds of many people. When 16 ounces of alcohol are burnt in an apparatus6 properly
adapted for collecting all the water disengaged during the combustion, we obtain from 17
to 18 ounces of water. As no substance can furnish a product larger than its original bulk,
it follows, that something else has united with the alcohol during its combustion; and I
have already shown that this must be oxygen, or the base of air. Thus alcohol contains
hydrogen, which is one of the elements of water; and the atmospheric air contains
oxygen, which is the other element necessary to the composition of water. This
experiment is a new proof that water is a compound substance.
6 See an account of this apparatus in the third part of this work.—Author.
98
Lavoisier
Elements of Chemistry
PART I
CHAPTER V
Of the Decomposition of Oxygen Gas by Sulfur, Phosphorus, and
Charcoal—and of the Formation of Acids in general.
In performing experiments, it is a necessary principle, which ought never to be deviated
from, that they be simplified as much as possible, and that every circumstance capable of
rendering their results complicated be carefully removed. Wherefore, in the experiments
which form the object of this chapter, we have never employed atmospheric air, which is
not a simple substance. It is true that the azotic gas, which forms a part of its mixture,
appears to be merely passive during combustion and calcination; but, besides that it
retards these operations very considerably, we are not certain but it may even alter their
results in some circumstances; for which reason I have thought it necessary to remove
even this possible cause of doubt, by only making use of pure oxygen gas in the
following experiments, which show the effects produced by combustion in that gas; and I
shall advert to such differences as take place in the results of these, when the oxygen gas,
or pure vital air, is mixed, in different proportions, with azotic gas.
Having filled a bell-glass (Fig. 3),
of between five and six pints measure,
with oxygen gas, I removed it from the
water trough, where it was filled, into the
quicksilver bath, by means of a shallow
glass dish slipped underneath, and
having dried the mercury, I introduced
61¼ grains of Kunkel's phosphorus in
two little China cups, like that
represented at D, Fig. 3. under the glass
A; and that I might set fire to each of the
portions of phosphorus separately, and to
prevent the one from catching fire from
the other, one of the dishes was covered
with a piece of flat glass. I next raised the quicksilver in the bell-
glass up to E F, by sucking out a sufficient portion of the gas by
means of the syphon G H I. After this, by means of the crooked iron
wire (Fig. 16.), made red hot, I set fire to the two portions of
phosphorus successively, first burning that portion which was not covered with the piece
of glass. The combustion was extremely rapid, attended with a very brilliant flame, and
considerable disengagement of light and heat. In consequence of the great heat induced,
the gas was at first much dilated, but soon after the mercury returned to its level, and a
considerable absorption of gas took place; at the same time, the whole inside of the glass
became covered with white light flakes of concrete phosphoric acid.
99
At the beginning of the experiment, the quantity of oxygen gas, reduced, as above
directed, to a common standard, amounted to 162 cubic inches; and, after the combustion
was finished, only 23¼ cubic inches, likewise reduced to the standard, remained; so that
the quantity of oxygen gas absorbed during the combustion was 138¾ cubic inches, equal
to 69.375 grains.
A part of the phosphorus remained unconsumed in the bottom of the cups, which
being washed on purpose to separate the acid, weighed about 16¼ grains; so that about
45 grains of phosphorus had been burned: But, as it is hardly possible to avoid an error of
one or two grains, I leave the quantity so far qualified. Hence, as nearly 45 grains of
phosphorus had, in this experiment, united with 69.375 grains of oxygen, and as no
gravitating matter could have escaped through the glass, we have a right to conclude, that
the weight of the substance resulting from the combustion in form of white flakes, must
equal that of the phosphorus and oxygen employed, which amounts to 114.375 grains.
And we shall presently find, that these flakes consisted entirely of a solid or concrete
acid. When we reduce these weights to hundredth parts, it will be found, that 100 parts of
phosphorus require 154 parts of oxygen for saturation, and that this combination will
produce 254 parts of concrete phosphoric acid, in form of white fleecy flakes.
This experiment proves, in the most convincing manner, that, at a certain degree
of temperature, oxygen possesses a stronger elective attraction, or affinity, for
phosphorus than for caloric; that, in consequence of this, the phosphorus attracts the base
of oxygen gas from the caloric, which, being set free, spreads itself over the surrounding
bodies. But, though this experiment be so far perfectly conclusive, it is not sufficiently
rigorous, as, in the apparatus described, it is impossible to ascertain the weight of the
flakes of concrete acid which are formed; we can therefore only determine this by
calculating the weights of oxygen and phosphorus employed; but as, in physics, and in
chemistry, it is not allowable to suppose what is capable of being ascertained by direct
experiment, I thought it necessary to repeat this experiment, as follows, upon a larger
scale, and by means of a different apparatus.
I took a large glass balloon (Fig. 4.) with an
opening three inches diameter, to which was fitted
a crystal stopper ground with emery, and pierced
with two holes for the tubes yyy, xxx. Before
shutting the balloon with its stopper, I introduced
the support BC, surmounted by the china cup D,
containing 150 grs. of phosphorus; the stopper was
then fitted to the opening of the balloon, coated
with a fat lute, and covered with slips of linen
spread with quick-lime and white of eggs: When
the lute was perfectly dry, the weight of the whole
apparatus was determined to within a grain, or a
grain and a half. I next exhausted the balloon, by
means of an air pump applied to the tube xxx, and then introduced oxygen gas by means
of the tube yyy, having a stop cock adapted to it. This kind of experiment is most readily
and most exactly performed by means of the hydro-pneumatic machine described by Mr.
Meusnier and me in the Memoirs of the Academy for 1782, p. 466, and explained in the
100
latter part of this work, with several important additions and corrections since made to it
by Mr. Meusnier. With this instrument we can readily ascertain, in the most exact
manner, both the quantity of oxygen gas introduced into the balloon, and the quantity
consumed during the course of the experiment.
When all things were properly disposed, I set fire to the phosphorus with a
burning glass. The combustion was extremely rapid, accompanied with a bright flame
and much heat; as the operation went on, large quantities of white flakes attached
themselves to the inner surface of the balloon, so that at last it was rendered quite opaque.
The quantity of these flakes at last became so abundant, that, although fresh oxygen gas
was continually supplied, which ought to have supported the combustion, yet the
phosphorus was soon extinguished. Having allowed the apparatus to cool completely, I
first ascertained the quantity of oxygen gas employed, and weighed the balloon
accurately, before it was opened. I next washed, dried, and weighed the small quantity of
phosphorus remaining in the cup, on purpose to determine the whole quantity of
phosphorus consumed in the experiment; this residuum of the phosphorus was of a
yellow ochre color. It is evident that by these several precautions I could easily
determine, 1st, the weight of the phosphorus consumed; 2d, the weight of the flakes
produced by the combustion; and, 3d, the weight of the oxygen which had combined with
the phosphorus. This experiment gave very nearly the same results with the former, as it
proved that the phosphorus, during its combustion, had absorbed a little more than one
and a half its weight of oxygen; and I learned with more certainty, that the weight of the
new substance, produced in the experiment, exactly equaled the sum of the weights of the
phosphorus consumed, and oxygen absorbed, which indeed was easily determinable a
priori. If the oxygen gas employed be pure, the residuum after combustion is as pure as
the gas employed; this proves that nothing escapes from the phosphorus, capable of
altering the purity of the oxygen gas, and that the only action of the phosphorus is to
separate the oxygen from the caloric, with which it was before united.
I mentioned above, that when any combustible body is burnt in a hollow sphere of
ice, or in an apparatus properly constructed upon that principle, the quantity of ice melted
during the combustion is an exact measure of the quantity of caloric disengaged. Upon
this head, the memoir given by M. de la Place and me, Aº. 1780, p. 355, may be
consulted. Having submitted the combustion of phosphorus to this trial, we found that
one pound of phosphorus melted a little more than 100 pounds of ice during its
combustion.
The combustion of phosphorus succeeds equally well in atmospheric air as in
oxygen gas, with this difference, that the combustion is vastly slower, being retarded by
the large proportion of azotic gas mixed with the oxygen gas, and that only about one-
fifth part of the air employed is absorbed, because as the oxygen gas only is absorbed, the
proportion of the azotic gas becomes so great toward the close of the experiment, as to
put an end to the combustion.
I have already shown, that phosphorus is changed by combustion into an
extremely light, white, flakey matter; and its properties are entirely altered by this
transformation: From being insoluble in water, it becomes not only soluble, but so greedy
of moisture as to attract the humidity of the air with astonishing rapidity; by this means it
is converted into a liquid, considerably more dense, and of more specific gravity than
101
water. In the state of phosphorus before combustion, it had scarcely any sensible taste; by
its union with oxygen it acquires an extremely sharp and sour taste. In a word, from one
of the class of combustible bodies it is changed into an incombustible substance, and
becomes one of those bodies called acids.
This property of a combustible substance to be converted into an acid, by the
addition of oxygen, we shall presently find belongs to a great number of bodies:
Wherefore, strict logic requires that we should adopt a common term for indicating all
these operations which produce analogous results; this is the true way to simplify the
study of science, as it would be quite impossible to bear all its specific details in the
memory, if they were not classically arranged. For this reason, we shall distinguish this
conversion of phosphorus into an acid, by its union with oxygen, and in general every
combination of oxygen with a combustible substance, by the term of oxygenation: from
which I shall adopt the verb to oxygenate, and of consequence shall say, that in
oxygenating phosphorus we convert it into an acid.
Sulfur is likewise a combustible body, or, in other words, it is a body which
possesses the power of decomposing oxygen gas, by attracting the oxygen from the
caloric with which it was combined. This can very easily be proved, by means of
experiments quite similar to those we have given with phosphorus; but it is necessary to
premise, that in these operations with sulfur, the same accuracy of result is not to be
expected as with phosphorus; because the acid which is formed by the combustion of
sulfur is difficultly condensable, and because sulfur burns with more difficulty, and is
soluble in the different gasses. But I can safely assert, from my own experiments, that
sulfur in burning absorbs oxygen gas; that the resulting acid is considerably heavier than
the sulfur burnt; that its weight is equal to the sum of the weights of the sulfur which has
been burnt, and of the oxygen absorbed; and, lastly that this acid is weighty,
incombustible, and miscible with water in all proportions: The only uncertainty
remaining upon this head, is with regard to the proportions of sulfur and of oxygen which
enter into the composition of the acid.
Charcoal, which, from all our present knowledge regarding it, must be considered
as a simple combustible body, has likewise the property of decomposing oxygen gas, by
absorbing its base from the caloric: But the acid resulting from this combustion does not
condense in the common temperature; under the pressure of our atmosphere, it remains in
the state of gas, and requires a large proportion of water to combine with or be dissolved
in. This acid has, however, all the known properties of other acids, though in a weaker
degree, and combines, like them, with all the bases which are susceptible of forming
neutral salts.
The combustion of charcoal in oxygen gas may be effected like that of
phosphorus in the bell glass (Fig. 3) placed over mercury: but, as the heat of red hot iron
is not sufficient to set fire to the charcoal, we must add a small morsel of tinder, with a
minute particle of phosphorus, in the same manner as directed in the experiment for the
combustion of iron. A detailed account of this experiment will be found in the memoirs
of the academy for 1781, p. 448. By that experiment it appears that 28 parts by weight of
charcoal require 72 parts of oxygen for saturation and that the aeriform acid produced is
precisely equal in weight to the sum of the weights of the charcoal and oxygen gas
employed. This aeriform acid was called fixed or fixable air by the chemists who first
102
discovered it; they did not then know whether it was air resembling that of the
atmosphere, or some other elastic fluid, vitiated and corrupted by combustion; but since it
is now ascertained to be an acid, formed like all others by the oxygenation of its peculiar
base, it is obvious that the name of fixed air is quite ineligible.1
By burning charcoal in the apparatus mentioned [p. 100], Mr. de la Place and I
found that one lib. of charcoal melted 96 libs. 6 oz. of ice; that, during the combustion, 2
libs. 9 oz. 1 gros. 10 grs. of oxygen were absorbed, and that 3 libs. 9 oz. 1 gros. 10 grs. of
acid gas were formed. This gas weighs 0.695 parts of a grain for each cubic inch, in the
common standard temperature and pressure mentioned above, so that 34,242 cube inches
of acid gas are produced by the combustion of one pound of charcoal.
I might multiply these experiments, and show by a numerous succession of facts
that all acids are formed by the combustion of certain substances; but I am prevented
from doing so in place, by the plan which I have laid down, of proceeding only from facts
already ascertained, to such as are unknown, and of drawing my examples only from
circumstances already explained. In the meantime, however, the three examples above
cited may suffice for giving a clear and accurate conception of the manner in which acids
are formed. By these it may be clearly seen that oxygen is an element common to them
all, which constitutes their acidity; and that they differ from each other, according to the
nature of the oxygenated or acidified substance. We must therefore, in every acid,
carefully distinguish between the acidifiable base, which Mr. de Morveau calls the
radical, and the acidifiing principle, or oxygen.
CHAPTER VI
Of the Nomenclature of Acids in general, and particularly of those
drawn from Nitre and Sea-Salt.
It becomes extremely easy, from the principles laid down in the preceding chapter, to
establish a systematic nomenclature for the acids: The word acid, being used as a generic
term, each acid falls to be distinguished in language, as in nature, by the name of its base
or radical. Thus, we give the generic name of acids to the products of the combustion or
oxygenation of phosphorus, of sulfur, and of charcoal; and these products are respectively
named the phosphoric acid, the sulfuric acid, and the carbonic acid.
There is however, a remarkable circumstance in the oxygenation of combustible
bodies, and of a part of such bodies as are convertible into acids, that they are susceptible
of different degrees of saturation with oxygen, and that the resulting acids, though formed
by the union of the same elements, are possessed of different properties, depending upon
that difference of proportion. Of this, the phosphoric acid, and more especially the
sulfuric, furnishes us with examples. When sulfur is combined with a small proportion of
oxygen, it forms, in this first or lower degree of oxygenation, a volatile acid, having a
penetrating odor, and possessed of very particular qualities. By a larger proportion of
oxygen, it is changed into a fixed, heavy acid, without any odor, and which, by
1 It may be proper to remark, though here omitted by the author, that, in conformity with the general
principles of the new nomenclature, this acid is by Mr. Lavoisier and his colleagues called the carbonic
acid, and when in the aeriform state carbonic acid gas.—Translator.
103
combination with other bodies, gives products quite different from those furnished by the
former. In this instance, the principles of our nomenclature seem to fail; and it seems
difficult to derive such terms from the name of the acidifiable base, as shall distinctly
express these two degrees of saturation, or oxygenation, without circumlocution. By
reflection, however, upon the subject, or perhaps rather from the necessity of the case, we
have thought it allowable to express these varieties in the oxygenation of the acids, by
simply varying the termination of their specific names. The volatile acid produced from
sulfur was anciently known to Stahl under the name of sulfurous acid.2 We have
preserved that term for this acid from sulfur under-saturated with oxygen; and distinguish
the other, or completely saturated or oxygenated acid, by the name of sulfuric acid. We
shall therefore say, in this new chemical language, that sulfur, in combining with oxygen,
is susceptible of two degrees of saturation; that the first, or lesser degree, constitutes
sulfurous acid, which is volatile and penetrating; whilst the second, or higher degree of
saturation, produces sulfuric acid, which is fixed and inodorous. We shall adopt this
difference of termination for all the acids which assume several degrees of saturation.
Hence we have a phosphorous and a phosphoric acid, an acetous and an acetic acid; and
so on, for others in similar circumstances.
This part of chemical science would have been extremely simple, and the
nomenclature of the acids would not have been at all perplexed, as it is now in the old
nomenclature, if the base or radical of each acid had been known when the acid itself was
discovered. Thus, for instance, phosphorus being a known substance before the discovery
of its acid, this latter was rightly distinguished by a term drawn from the name of its
acidifiable base. But when, on the contrary, an acid happened to be discovered before its
base, or rather, when the acidifiable base from which it was formed remained unknown,
names were adopted for the two, which have not the smallest connection; and thus, not
only the memory became burthened with useless appellations, but even the minds of
students, nay even of experienced chemists, became filled with false ideas, which time
and reflection alone is capable of eradicating. We may give an instance of this confusion
with respect to the acid sulfur: The former chemists, having procured this acid from the
vitriol of iron, gave it the name of the vitriolic acid from the name of the substance which
produced it; and they were then ignorant that the acid procured from sulfur by
combustion was exactly the same.
The same thing happened with the aeriform acid formerly called fixed air; it not
being known that this acid was the result of combining charcoal with oxygen, a variety of
denominations have been given to it, not one of which conveys just ideas of its nature or
origin. We have found it extremely easy to correct and modify the ancient language with
respect to these acids proceeding from known bases, having converted the name of
vitriolic acid into that of sulfuric, and the name of fixed air into that of carbonic acid; but
it is impossible to follow this plan with the acids whose bases are still unknown; with
these we have been obliged to use a contrary plan, and, instead of forming the name of
the acid from that of its base, have been forced to denominate the unknown base from the
2 The term formerly used by the English chemists for this acid was written sulfureous; but we have thought
proper to spell it as above, that it may better conform with the similar terminations of nitrous, carbonous,
&c. to be used hereafter. In general, we have used the English terminations ic and ous to translate the terms
of the Author which end with ique and cux, with hardly any other alterations.—Translator.
104
name of the known acid, as happens in the case of the acid which is procured from sea
salt.
To disengage this acid from the alkaline base with which it is combined, we have
only to pour sulfuric acid upon sea-salt, immediately a brisk effervescence takes place,
white vapors arise, of a very penetrating odor, and, by only gently heating the mixture, all
the acid is driven off. As, in the common temperature and pressure of our atmosphere,
this acid is naturally in the state of gas, we must use particular precautions for retaining it
in proper vessels. For small experiments, the most
simple and most commodious apparatus consists of a
small retort G (Fig. 5.) into which the sea-salt is
introduced, well dried,3 we then pour on some
concentrated sulfuric acid, and immediately introduce
the beak of the retort under little jars or bell-glasses A,
(same Fig.), previously filled with quicksilver. In
proportion as the acid gas is disengaged, it passes into
the jar, and gets to the top of the quicksilver, which it
displaces. When the disengagement of the gas
slackens, a gentle heat is applied to the retort, and
gradually increased till nothing more passes over. This acid gas has a very strong affinity
with water, which absorbs an enormous quantity of it, as is proved by introducing a very
thin layer of water into the glass which contains the gas; for, in an instant, the whole acid
gas disappears, and combines with the water.
This latter circumstance is taken advantage of in laboratories and manufactures,
on purpose to obtain the acid of sea-salt in a liquid form; and for this purpose the
apparatus (Fig. 1.) is employed. It consists, first, of a tubulated retort A, into which the
sea-salt, and after it the sulfuric acid, are introduced through the opening H; second, of
the balloon or recipient c, b, intended for containing the small quantity of liquid which
passes over during the process; and third, of a set of bottles, with two mouths, L, L, L, L,
half filled with water, intended for absorbing the gas disengaged by the distillation. This
apparatus will be more amply described in the latter part of this work.
Although we have not yet been able, either to compose or to decompound this
acid of sea-salt, we cannot have the smallest doubt that it, like all other acids, is
3 For this purpose, the operation called decrepitation is used, which consists in subjecting it to nearly a red
heat, in a proper vessel, so as to evaporate all its water of crystallization.—Translator.
105
composed by the union of oxygen with an acidifiable base. We have therefore called this
unknown substance the muriatic base, or muriatic radical, deriving this name, after the
example of Mr. Bergman and Mr. de Morveau, from the Latin word muria, which was
anciently used to signify sea-salt. Thus, without being able exactly to determine the
component parts of muriatic acid, we design, by that term, a volatile acid, which retains
the form of gas in the common temperature and pressure of our atmosphere, which
combines with great facility, and in great quantity, with water, and whose acidifiable base
adheres so very intimately with oxygen, that no method has hitherto been devised for
separating them. If ever this acidifiable base of the muriatic acid is discovered to be a
known substance, though now unknown in that capacity, it will be requisite to change its
present denomination for one analogous with that of its base.
In common with sulfuric acid, and several other acids, the muriatic is capable of
different degrees of oxygenation; but the excess of oxygen produces quite contrary
effects upon it from what the same circumstance produces upon the acid of sulfur. The
lower degree of oxygenation converts sulfur into a volatile gaseous acid, which only
mixes in small proportions with water, whilst a higher oxygenation forms an acid
possessing much stronger acid properties, which is very fixed and cannot remain in the
state of gas but in a very high temperature, which has no smell, and which mixes in large
proportion with water. With muriatic acid, the direct reverse takes place; an additional
saturation with oxygen renders it more volatile, of a more penetrating odor, less miscible
with water, and diminishes its acid properties. We were at first inclined to have
denominated these two degrees of saturation in the same manner as we had done with the
acid of sulfur, calling the less oxygenated muriatous acid, and that which is more
saturated with oxygen muriatic acid: But, as this latter gives very particular results in its
combinations, and as nothing analogous to it is yet known in chemistry, we have left the
name of muriatic acid to the less saturated, and give the latter the more compounded
appellation of oxygenated muriatic acid.
Although the base or radical of the acid which is extracted from nitre or saltpetre
be better known, we have judged proper only to modify its name in the same manner with
that of the muriatic acid. It is drawn from nitre, by the intervention of sulfuric acid, by a
process similar to that described for extracting the muriatic acid, and by means of the
same apparatus (Fig. 1.). In proportion as the acid passes over, it is in part condensed in
the balloon or recipient, and the rest is absorbed by the water contained in the bottles L,
L, L, L; the water becomes first green, then blue, and at last yellow, in proportion to the
concentration of the acid. During this operation, a large quantity of oxygen gas, mixed
with a small proportion of azotic gas, is disengaged.
This acid, like all others, is composed of oxygen, united to an acidifiable base,
and is even the first acid in which the existence of oxygen was well ascertained. Its two
constituent elements are but weakly united, and are easily separated, by presenting any
substance with which oxygen has a stronger affinity than with the acidifiable base
peculiar to this acid. By some experiments of this kind, it was first discovered that azote,
or the base of mephitis or azotic gas, constituted its acidifiable base or radical; and
consequently that the acid of nitre was really an azotic acid, having azote for its base,
combined with oxygen. For these reasons, that we might be consistent with our
principles, it appeared necessary, either to call the acid by the name of azotic, or to name
106
the base nitric radical; but from either of these we were dissuaded, by the following
considerations. In the first place, it seemed difficult to change the name of nitre or
saltpetre, which has been universally adopted in society, in manufactures, and in
chemistry; and, on the other hand, azote having been discovered by Mr. Berthollet to be
the base of volatile alkali, or ammoniac, as well as of this acid, we thought it improper to
call it nitric radical. We have therefore continued the term of azote to the base of that part
of atmospheric air which is likewise the nitric and ammoniacal radical; and we have
named the acid of nitre, in its lower and higher degrees of oxygenation, nitrous acid in
the former, and nitric acid in the latter state; thus preserving its former appellation
properly modified.
Several very respectable chemists have disapproved of this deference for the old
terms, and wished us to have persevered in perfecting a new chemical language, without
paying any respect for ancient usage; so that, by thus steering a kind of middle course, we
have exposed ourselves to the censures of one sect of chemists, and to the expostulations
of the opposite party.
The acid of nitre is susceptible of assuming a great number of separate states,
depending upon its degree of oxygenation, or upon the proportions in which azote and
oxygen enter into its composition. By a first or lowest degree of oxygenation, it forms a
particular species of gas, which we shall continue to name nitrous gas; this is composed
nearly of two parts, by weight, of oxygen combined with one part of azote; and in this
state it is not miscible with water. In this gas, the azote is by no means saturated with
oxygen, but, on the contrary, has still a very great affinity for that element, and even
attracts it from atmospheric air, immediately upon getting into contact with it. This
combination of nitrous gas with atmospheric air has even become one of the methods for
determining the quantity of oxygen contained in air, and consequently for ascertaining its
degree of salubrity.
This addition of oxygen converts the nitrous gas into a powerful acid, which has a
strong affinity with water, and which is itself susceptible of various additional degrees of
oxygenation. When the proportions of oxygen and azote is below three parts, by weight,
of the former, to one of the latter, the acid is red colored, and emits copious fumes. In this
state, by the application of a gentle heat, it gives out nitrous gas; and we term it, in this
degree of oxygenation, nitrous acid. When four parts, by weight, of oxygen, are
combined with one part of azote, the acid is clear and colorless, more fixed in the fire
than the nitrous acid, has less odor, and its constituent elements are more firmly united.
This species of acid, in conformity with our principles of nomenclature, is called nitric
acid.
Thus, nitric acid is the acid of nitre, surcharged with oxygen; nitrous acid is the
acid of nitre surcharged with azote; or, what is the same thing, with nitrous gas; and this
latter is azote not sufficiently saturated with oxygen to possess the properties of an acid.
To this degree of oxygenation, we have afterwards, in the course of this work, given the
generic name of oxide.4
4 In strict conformity with the principles of the new nomenclature, but which the Author has given his
reasons for deviating from in this instance, the following ought to have been the terms for azote, in its
several degrees of oxygenation: Azote, azotic gas (azote combined with caloric), azotic oxide gas, nitrous
107
CHAPTER VII
Of the Decomposition of Oxygen Gas by means of Metals,
and the Formation of Metallic Oxides
Oxygen has a stronger affinity with metals heated to a certain degree than with caloric; in
consequence of which, all metallic bodies, excepting gold, silver, and platina, have the
property of decomposing oxygen gas, by attracting its base from the caloric with which it
was combined. We have already shown in what manner this decomposition takes place,
by means of mercury and iron; having observed, that, in the case of the first, it must be
considered as a kind of gradual combustion, whilst in the latter, the combustion is
extremely rapid and attended with a brilliant flame. The use of the heat employed in these
operations is to separate the particles of the metal from each other, and to diminish their
attraction of cohesion or aggregation, or, what is the same thing, their mutual attraction
for each other.
The absolute weight of metallic substances is augmented in proportion to the
quantity of oxygen they absorb; they, at the same time, lose their metallic splendor, and
are reduced into an earthy pulverulent matter. In this state metals must not be considered
as entirely saturated with oxygen, because their action upon this element is
counterbalanced by the power of affinity between it and caloric. During the calcination of
metals, the oxygen is therefore acted upon by two separate and opposite powers, that of
its attraction for caloric, and that exerted by the metal, and only tends to unite with the
latter in consequence of the excess of the latter over the former, which is, in general, very
inconsiderable. Wherefore, when metallic substances are oxygenated in atmospheric air,
or in oxygen gas, they are not converted into acids like sulfur, phosphorus, and charcoal,
but are only changed into intermediate substances, which, though approaching to the
nature of salts, have not acquired all the saline properties. The old chemists have affixed
the name of calx not only to metals in this state, but to every body which has been long
exposed to the action of fire without being melted. They have converted this word calx
into a generic term, under which they confound (1) calcareous earth, which, from a
neutral salt, which it really was before calcination, has been changed by fire into an
earthy alkali, by losing half of its weight, with (2) metals which, by the same means, have
joined themselves to a new substance, whose quantity often exceeds half their weight,
and by which they have been changed almost into the nature of acids. This mode of
classifying substances of so very opposite natures, under the same generic name, would
have been quite contrary to our principles of nomenclature, especially as, by retaining the
above term for this state of metallic substances, we must have conveyed very false ideas
of its nature. We have, therefore, laid aside the expression metallic calx altogether, and
have substituted in its place the term oxide, from the Greek word οξυς.
By this may be seen, that the language we have adopted is both copious and
expressive. The first or lowest degree of oxygenation in bodies, converts them into
oxides; a second degree of additional oxygenation constitutes the class of acids, of which
the specific names, drawn from their particular bases, terminate in ous, as the nitrous and
sulfurous acids; the third degree of oxygenation changes these into the species of acids
distinguished by the termination in ic, as the nitric and sulfuric acids; and, lastly, we can
acid, and nitric acid.—Translator.
108
express a fourth, or highest degree of oxygenation, by adding the word oxygenated to the
name of the acid, as has been already done with the oxygenated muriatic acid.
We have not confined the term oxide to expressing the combinations of metals
with oxygen, but have extended it to signify that first degree of oxygenation in all bodies,
which, without converting them into acids, causes them to approach to the nature of salts.
Thus, we give the name of oxide of sulfur to that soft substance into which sulfur is
converted by incipient combustion; and we call the yellow matter left by phosphorus,
after combustion, by the name of oxide of phosphorus. In the same manner, nitrous gas,
which is azote in its first degree of oxygenation, is the oxide of azote. We have likewise
oxides in great numbers from the vegetable and animal kingdoms; and I shall show, in the
sequel, that this new language throws great light upon all the operations of art and nature.
We have already observed that almost all the metallic oxides have peculiar and
permanent colors. These vary not only in the different species of metals, but even
according to the various degrees of oxygenation in the same metal. Hence we are under
the necessity of adding two epithets to each oxide, one of which indicates the metal
oxidized, while the other indicates the peculiar color of the oxide. Thus, we have the
black oxide of iron, the red oxide of iron, and the yellow oxide of iron; which expressions
respectively answer to the old unmeaning terms of martial ethiops, colcothar, and rust of
iron, or ochre. We have likewise the gray, yellow, and red oxides of lead, which answer
to the equally false or insignificant terms, ashes of lead, massicot, and minium.
These denominations sometimes become rather long, especially when we mean to
indicate whether the metal has been oxidized in the air, by detonation with nitre, or by
means of acids; but then they always convey just and accurate ideas of the corresponding
object which we wish to express by their use. All this will be rendered perfectly clear and
distinct by means of the tables which are added to this work….
CHAPTER XVI
Of the Formation of Neutral Salts, and of their different Bases
We have just seen that all the oxides and acids from the animal and vegetable kingdoms
are formed by means of a small number of simple elements, or at least of such as have
not hitherto been susceptible of decomposition, by means of combination with oxygen;
these are azote, sulfur, phosphorus, charcoal, hydrogen, and the muriatic radical.1 We
may justly admire the simplicity of the means employed by nature to multiply qualities
and forms, whether by combining three or four acidifiable bases in different proportions,
or by altering the dose of oxygen employed for oxidizing or acidifying them. We shall
find the means no less simple and diversified, and as abundantly productive of forms and
qualities, in the order of bodies we are now about to treat of.
1 I have not ventured to omit this element, as here enumerated with the other principles of animal and
vegetable substances, though it is not at all taken notice of in the preceding chapters as entering into the
composition of these bodies.—Translator.
109
Acidifiable substances, by combining with oxygen, and their consequent
conversion into acids, acquire great susceptibility of farther combination; they become
capable of uniting with earthy and metallic bodies, by which means neutral salts are
formed. Acids may therefore be considered as true salifying principles, and the
substances with which they unite to form neutral salts may be called salifiable bases: The
nature of the union which these two principles form with each other is meant as the
subject of the present chapter.
This view of the acids prevents me from considering them as salts, though they
are possessed of many of the principal properties of saline bodies, as solubility in water,
&c. I have already observed that they are the result of a first order of combination, being
composed of two simple elements, or at least of elements which act as if they were
simple, and we may therefore rank them, to use the language of Stahl, in the order of
mixts. The neutral salts, on the contrary, are of a secondary order of combination, being
formed by the union of two mixts with each other, and may therefore be termed
compounds. Hence I shall not arrange the alkalis2 or earths in the class of salts, to which I
allot only such as are composed of an oxygenated substance united to a base.
I have already enlarged sufficiently upon the formation of acids in the preceding
chapter, and shall not add anything farther upon that subject; but having as yet given no
account of the salifiable bases, which are capable of uniting with them to form neutral
salts, I mean in this chapter to give an account of the nature and origin of each of these
bases. These are potash, soda, ammoniac, lime, magnesia, barytes, alumina, and all the
metallic bodies.
§ 1. Of Potash
We have already shown that when a vegetable substance is submitted to the action
of fire in distilling vessels, its component elements, oxygen, hydrogen, and charcoal,
which formed a threefold combination in a state of equilibrium, unite, two and two, in
obedience to affinities which act conformable to the degree of heat employed. Thus, at
the first application of the fire, whenever the heat produced exceeds the temperature of
boiling water, part of the oxygen and hydrogen unite to form water; soon after the rest of
the hydrogen, and part of the charcoal, combine into oil; and, lastly, when the fire is
pushed to the red heat, the oil and water, which had been formed in the early part of the
process, become again decomposed, the oxygen and charcoal unite to form carbonic acid,
a large quantity of hydrogen gas is set free, and nothing but charcoal remains in the retort.
A great part of these phenomena occur during the combustion of vegetables in the
open air; but, in this case, the presence of the air introduces three new substances, the
oxygen and azote of the air and caloric, of which two at least produce considerable
changes in the results of the operation. In proportion as the hydrogen of the vegetable, or
that which results from the decomposition of the water, is forced out in the form of
hydrogen gas by the progress of the fire, it is set on fire immediately upon getting in
contact with the air, water is again formed, and the greater part of the caloric of the two
gasses becoming free produces flame. When all the hydrogen gas is driven out, burnt, and
2 Perhaps my thus rejecting the alkalis from the class of salts may be considered as a capital defect in the
method I have adopted, and I am ready to admit the charge; but this inconvenience is compensated by so
many advantages, that I could not think it of sufficient consequence to make me alter my plan.—Author.
110
again reduced to water, the remaining charcoal continues to burn, but without flame; it is
formed into carbonic acid, which carries off a portion of caloric sufficient to give it the
gaseous form; the rest of the caloric, from the oxygen of the air, being set free, produces
the heat and light observed during the combustion of charcoal. The whole vegetable is
thus reduced into water and carbonic acid, and nothing remains but a small portion of
gray earthy matter called ashes, being the only really fixed principles which enter into the
constitution of vegetables.
The earth, or rather ashes, which seldom exceeds a twentieth part of the weight of
the vegetable, contains a substance of a particular nature, known under the name of fixed
vegetable alkali, or potash. To obtain it, water is poured upon the ashes, which dissolves
the potash and leaves the ashes which are insoluble; by afterwards evaporating the water,
we obtain the potash in a white concrete form: It is very fixed even in a very high degree
of heat. I do not mean here to describe the art of preparing potash or the method of
procuring it in a state of purity, but have entered upon the above detail that I might not
use any word not previously explained.
The potash obtained by this process is always less or more saturated with carbonic
acid, which is easily accounted for: As the potash does not form, or at least is not set free,
but in proportion as the charcoal of the vegetable is converted into carbonic acid by the
addition of oxygen, either from the air or the water, it follows that each particle of potash,
at the instant of its formation, or at least of its liberation, is in contact with a particle of
carbonic acid, and, as there is a considerable affinity between these two substances, they
naturally combine together. Although the carbonic acid has less affinity with potash than
any other acid, yet it is difficult to separate the last portions from it. The most usual
method of accomplishing this is to dissolve the potash in water; to this solution add two
or three times its weight of quick-lime, then filtrate the liquor and evaporate it in close
vessels; the saline substance left by the evaporation is potash almost entirely deprived of
carbonic acid. In this state it is soluble in an equal weight of water, and even attracts the
moisture of the air with great avidity; by this property it furnishes us with an excellent
means of rendering air or gas dry by exposing them to its action. In this state it is soluble
in alcohol, though not when combined with carbonic acid; and Mr. Berthollet employs
this property as a method of procuring potash in the state of perfect purity.
All vegetables yield less or more of potash in consequence of combustion, but it is
furnished in various degrees of purity by different vegetables; usually, indeed, from all of
them it is mixed with different salts from which it is easily separable. We can hardly
entertain a doubt that the ashes, or earth which is left by vegetables in combustion, pre-
existed in them before they were burnt, forming what may be called the skeleton, or
osseous part of the vegetable. But it is quite otherwise with potash; this substance has
never yet been procured from vegetables but by means of processes or intermedia capable
of furnishing oxygen and azote, such as combustion, or by means of nitric acid; so that it
is not yet demonstrated that potash may not be a produce from these operations. I have
begun a series of experiments upon this object, and hope soon to be able to give an
account of their results.
111
§ 2. Of Soda
Soda, like potash, is an alkali procured by lixiviation from the ashes of burnt
plants, but only from those which grow upon the sea-side, and especially from the herb
kali, whence is derived the name alkali, given to this substance by the Arabians. It has
some properties in common with potash, and others which are entirely different: In
general, these two substances have peculiar characters in their saline combinations which
are proper to each, and consequently distinguish them from each other; thus soda, which,
as obtained from marine plants, is usually entirely saturated with carbonic acid, does not
attract the humidity of the atmosphere like potash, but, on the contrary, desiccates, its
crystals effloresce, and are converted into a white powder having all the properties of
soda, which it really is, having only lost its water of crystallization.
Hitherto we are not better acquainted with the constituent elements of soda than
with those of potash, being equally uncertain whether it previously existed ready formed
in the vegetable or is a combination of elements effected by combustion. Analogy leads
us to suspect that azote is a constituent element of all the alkalis, as is the case with
ammoniac; but we have only slight presumptions, unconfirmed by any decisive
experiments, respecting the composition of potash and soda.
§ 3. Of Ammoniac
We have, however, very accurate knowledge of the composition of ammoniac, or
volatile alkali, as it is called by the old chemists. Mr. Berthollet, in the Memoirs of the
Academy for 1784, p. 316, has proved by analysis that 1000 parts of this substance
consist of about 807 parts of azote combined with 193 parts of hydrogen.
Ammoniac is chiefly procurable from animal substances by distillation, during
which process the azote and hydrogen necessary to its formation unite in proper
proportions; it is not, however, procured pure by this process, being mixed with oil and
water, and mostly saturated with carbonic acid. To separate these substances it is first
combined with an acid, the muriatic for instance, and then disengaged from that
combination by the addition of lime or potash. When ammoniac is thus produced in its
greatest degree of purity it can only exist under the gaseous form, at least in the usual
temperature of the atmosphere; it has an excessively penetrating smell; it is absorbed in
large quantities by water, especially if cold and assisted by compression. Water thus
saturated with ammoniac has usually been termed volatile alkaline fluor; we shall call it
either simply ammoniac, or liquid ammoniac, and ammoniacal gas when it exists in the
aeriform state.
§ 4. Of Lime, Magnesia, Barytes, and Alumina
The composition of these four earths is totally unknown, and, until by new
discoveries their constituent elements are ascertained, we are certainly authorized to
consider them as simple bodies. Art has no share in the production of these earths, as they
are all procured ready formed from nature; but, as they have all, especially the three first,
great tendency to combination, they are never found pure. Lime is usually saturated with
carbonic acid in the state of chalk, calcareous spars, most of the marbles, &c.; sometimes
with sulfuric acid, as in gypsum and plaster stones; at other times with fluoric acid
forming vitreous or fluor spars; and lastly, it is found in the waters of the sea and of
112
saline springs, combined with muriatic acid. Of all the salifiable bases it is the most
universally spread through nature.
Magnesia is found in mineral waters, for the most part combined with sulfuric
acid; it is likewise abundant in sea-water, united with muriatic acid; and it exists in a
great number of stones of different kinds.
Barytes is much less common than the two preceding earths; it is found in the
mineral kingdom, combined with sulfuric acid, forming heavy spars, and sometimes,
though rarely, united to carbonic acid.
Alumina, or the base of alum, having less tendency to combination than the other
earths, is often found in the state of alumina, uncombined with any acid. It is chiefly
procurable from clays, of which, properly speaking, it is the base, or chief ingredient.
§ 5. Of Metallic Bodies
The metals, except gold, and sometimes silver, are rarely found in the mineral
kingdom in their metallic state, being usually less or more saturated with oxygen, or
combined with sulfur, arsenic, sulfuric acid, muriatic acid, carbonic acid, or phosphoric
acid. Metallurgy, or the docimastic art, teaches the means of separating them from these
foreign matters; and for this purpose we refer to such chemical books as treat upon these
operations.
We are probably only acquainted as yet with a part of the metallic substances
existing in nature, as all those which have a stronger affinity to oxygen, than charcoal
possesses, are incapable of being reduced to the metallic state, and, consequently, being
only presented to our observation under the form of oxides, are confounded with earths. It
is extremely probable that barytes, which we have just now arranged with earths, is in
this situation; for in many experiments it exhibits properties nearly approaching to those
of metallic bodies. It is even possible that all the substances we call earths may be only
metallic oxides, irreducible by any hitherto known process.
Those metallic bodies we are at present acquainted with, and which we can reduce
to the metallic or reguline state, are the following seventeen:
1. Arsenic 7. Bismuth 13. Copper
2. Molybdenum 8. Antimony 14. Mercury
3. Tungsten 9. Zinc 15. Silver
4. Manganese 10. Iron 16. Platina
5. Nickel 11. Tin 17. Gold
6. Cobalt 12. Lead
I only mean to consider these as salifiable bases, without entering at all upon the
consideration of their properties in the arts, and for the uses of society. In these points of
view each metal would require a complete treatise, which would lead me far beyond the
bounds I have prescribed for this work.
113
CHAPTER XVII
Continuation of the Observations upon Salifiable Bases,
and the Formation of Neutral Salts.
It is necessary to remark that earths and alkalis unite with acids to form neutral salts
without the intervention of any medium, whereas metallic substances are incapable of
forming this combination without being previously less or more oxygenated; strictly
speaking, therefore, metals are not soluble in acids, but only metallic oxides. Hence,
when we put a metal into an acid for solution, it is necessary, in the first place, that it
become oxygenated, either by attracting oxygen from the acid or from the water; or, in
other words, that a metal cannot be dissolved in an acid unless the oxygen, either of the
acid, or of the water mixed with it, has a stronger affinity to the metal than to the
hydrogen or the acidifiable base; or, what amounts to the same thing, that no metallic
solution can take place without a previous decomposition of the water or the acid in
which it is made. The explanation of the principal phenomena of metallic solution
depends entirely upon this simple observation, which was overlooked even by the
illustrious Bergman.
The first and most striking of these is the effervescence, or, to speak less
equivocally, the disengagement of gas which takes place during the solution; in the
solutions made in nitric acid, this effervescence is produced by the disengagement of
nitrous gas; in solutions with sulfuric acid, it is either sulfurous acid gas or hydrogen gas,
according as the oxidation of the metal happens to be made at the expense of the sulfuric
acid or of the water. As both nitric acid and water are composed of elements which, when
separate, can only exist in the gaseous form, at least in the common temperature of the
atmosphere, it is evident that, whenever either of these is deprived of its oxygen, the
remaining element must instantly expand and assume the state of gas; the effervescence
is occasioned by this sudden conversion from the liquid to the gaseous state. The same
decomposition, and consequent formation of gas, takes place when solutions of metals
are made in sulfuric acid: In general, especially by the humid way, metals do not attract
all the oxygen it contains; they therefore reduce it, not into sulfur, but into sulfurous acid,
and as this acid can only exist as gas in the usual temperature, it is disengaged, and
occasions effervescence.
The second phenomenon is that when the metals have been previously oxidized,
they all dissolve in acids without effervescence: This is easily explained; because, not
having now any occasion for combining with oxygen, they neither decompose the acid
nor the water by which, in the former case, the effervescence is occasioned.
A third phenomenon, which requires particular consideration is that none of the
metals produce effervescence by solution in oxygenated muriatic acid. During this
process the metal, in the first place, carries off the excess of oxygen from the oxygenated
muriatic acid, by which it becomes oxidized, and reduces the acid to the state of ordinary
muriatic acid. In this case there is no production of gas, not that the muriatic acid does
not tend to exist in the gaseous state in the common temperature, which it does equally
with the acids formerly mentioned, but because this acid, which otherwise would expand
into gas, finds more water combined with the oxygenated muriatic acid than is necessary
to retain it in the liquid form; hence it does not disengage like the sulfurous acid, but
114
remains, and quietly dissolves and combines with the metallic oxide previously formed
from its superabundant oxygen.
The fourth phenomenon is that metals are absolutely insoluble in such acids as
have their bases joined to oxygen by a stronger affinity than these metals are capable of
exerting upon that acidifying principle. Hence silver, mercury, and lead, in their metallic
states, are insoluble in muriatic acid, but, when previously oxidized, they become readily
soluble without effervescence.
From these phenomena it appears that oxygen is the bond of union between
metals and acids; and from this we are led to suppose that oxygen is contained in all
substances which have a strong affinity with acids: Hence it is very probable the four
eminently salifiable earths contain oxygen, and their capability of uniting with acids is
produced by the intermediation of that element. What I have formerly noticed relative to
these earths is considerably strengthened by the above considerations, viz. that they may
very possibly be metallic oxides, with which oxygen has a stronger affinity than with
charcoal, and consequently not reducible by any known means.
All the acids hitherto known are enumerated in the following table, the first
column of which contains the names of the acids according to the new nomenclature, and
in the second column are placed the bases or radicals of these acids, with observations.
Names of the Acids Names of the Bases, with Observations
1. Sulphurous Sulfur.
2. Sulphuric
3. Phosphorous Phosphorus.
4. Phosphoric
5. Muriatic Muriatic radical or base, hitherto unknown.
6. Oxygenated muriatic
7. Nitrous
8. Nitric Azote.
9. Oxygenated nitric
10. Carbonic Charcoal.
11. Acetous
12. Acetic The bases or radicals of all these acids seem to be
13. Oxalic formed by a combination of charcoal and hydrogen;
14. Tartarous and the only difference seems to be owing to the different
15. Pyro-tartarous proportions in which these elements combine to form
16. Citric their bases, and to the different doses of oxygen in
17. Malic their acidification. A connected series of accurate
18. Pyro-lignous experiments is still wanted upon this subject.
19. Pyro-mucous
115
20. Gallic
21. Prussic Our knowledge of the bases of these acids
22. Benzoic is hitherto imperfect; we only know that
23. Succinic they contain hydrogen and charcoal as
24. Camphoric principal elements, and that the prussic acid
25. Lactic contains azote.
26. Saccholactic
27. Bombic The base of these and all acids procured from
28. Formic animal substances seems to consist of charcoal,
29. Sebacic hydrogen, phosphorous, and azote.
30. Boracic The bases of these two are hitherto
31. Fluoric entirely unknown.
32. Antimonic Antimony.
33. Argentic Silver.
34. Arseniac Arsenic.
35. Bismuthic Bismuth.
36. Cobaltic Cobalt.
37. Cupric Copper.
38. Stannic Tin.
39. Ferric Iron.
40. Manganic Manganese.
41. Mercuric Mercury.
42. Molybdic Molybdena.
43. Nickolic Nickel.
44. Auric Gold.
45. Platinic Platina.
46. Plumbic Lead.
47. Tungstic Tungsten.
48. Zincic Zinc.
In this list, which contains 48 acids, I have enumerated 17 metallic acids hitherto
very imperfectly known, but upon which Mr. Berthollet is about to publish a very
important work. It cannot be pretended that all the acids which exist in nature, or rather
all the acidifiable bases, are yet discovered; but, on the other hand, there are considerable
grounds for supposing that a more accurate investigation than has hitherto been attempted
will diminish the number of the vegetable acids, by showing that several of these, at
present considered as distinct acids, are only modifications of others. All that can be done
in the present state of our knowledge is to give a view of chemistry as it really is, and to
establish fundamental principles, by which such bodies as may be discovered in future
may receive names, in conformity with one uniform system.
The known salifiable bases, or substances capable of being converted into neutral
salts by union with acids, amount to 24; viz. 3 alkalis, 4 earths, and 17 metallic
substances; so that, in the present state of chemical knowledge, the whole possible
116
number of neutral salts amounts to 1152.3 This number is upon the supposition that the
metallic acids are capable of dissolving other metals, which is a new branch of chemistry
not hitherto investigated, upon which depends all the metallic combinations named
vitreous. There is reason to believe that many of these supposable saline combinations are
not capable of being formed, which must greatly reduce the real number of neutral salts
producible by nature and art. Even if we suppose the real number to amount only to five
or six hundred species of possible neutral salts, it is evident that, were we to distinguish
them, after the manner of the ancients, either by the names of their first discoverers, or by
terms derived from the substances from which they are procured, we should at last have
such a confusion of arbitrary designations, as no memory could possibly retain. This
method might be tolerable in the early ages of chemistry, or even till within these twenty
years, when only about thirty species of salts were known; but, in the present times, when
the number is augmenting daily, when every new acid gives us 24 or 48 new salts,
according as it is capable of one or two degrees of oxygenation, a new method is
certainly necessary. The method we have adopted, drawn from the nomenclature of the
acids, is perfectly analogical and, following nature in the simplicity of her operations,
gives a natural and easy nomenclature applicable to every possible neutral salt.
In giving names to the different acids, we express the common property by the
generic term acid, and distinguish each species by the name of its peculiar acidifiable
base. Hence the acids formed by the oxygenation of sulfur, phosphorus, charcoal, &c. are
called sulfuric acid, phosphoric acid, carbonic acid, &c. We thought it likewise proper to
indicate the different degrees of saturation with oxygen, by different terminations of the
same specific names. Hence we distinguish between sulfurous and sulfuric, and between
phosphorous and phosphoric acids, &c.
By applying these principles to the nomenclature of neutral salts, we give a
common term to all the neutral salts arising from the combination of one acid, and
distinguish the species by adding the name of the salifiable base. Thus, all the neutral
salts having sulfuric acid in their composition are named sulfats; those formed by the
phosphoric acid, phosphats, &c. The species being distinguished by the names of the
salifiable bases gives us sulfat of potash, sulfat of soda, sulfat of ammoniac, sulfat of
lime, sulfat of iron, &c. As we are acquainted with 24 salifiable bases, alkaline, earthy,
and metallic, we have consequently 24 sulfats, as many phosphats, and so on through all
the acids. Sulfur is, however, susceptible of two degrees of oxygenation, the first of
which produces sulfurous, and the second, sulfuric acid; and, as the neutral salts produced
by these two acids, have different properties, and are in fact different salts, it becomes
necessary to distinguish these by peculiar terminations; we have therefore distinguished
the neutral salts formed by the acids in the first or lesser degree of oxygenation, by
changing the termination at into ite, as sulfites, phosphites,4 &c. Thus, oxygenated or
3 This number excludes all triple salts, or such as contain more than one salifiable base, all the salts whose
bases are over or under saturated with acid, and those formed by the nitro-muriatic acid.—Translator. 4 As all the specific names of the acids in the new nomenclature are adjectives, they would have applied
severally to the various salifiable bases, without the invention of other terms, with perfect distinctness.
Thus, sulfurous potash, and sulfuric potash, are equally distinct as sulfite of potash, and sulfat of potash;
and have the advantage of being more easily retained in the memory, because more naturally arising from
the acids themselves, than the arbitrary terminations adopted by Mr. Lavoisier.—Translator.
117
acidified sulfur, in its two degrees of oxygenation is capable of forming 48 neutral salts,
24 of which are sulfites, and as many sulfats; which is likewise the case with all the acids
capable of two degrees of oxygenation.5
It were both tiresome and unnecessary to follow these denominations through all
the varieties of their possible application; it is enough to have given the method of
naming the various salts, which, when once well understood, is easily applied to every
possible combination. The name of the combustible and acidifiable body being once
known, the names of the acid it is capable of forming, and of all the neutral combinations
the acid is susceptible of entering into, are most readily remembered. Such as require a
more complete illustration of the methods in which the new nomenclature is applied will,
in the Second Part of this book, find Tables which contain a full enumeration of all the
neutral salts, and, in general, all the possible chemical combinations, so far as is
consistent with the present state of our knowledge. To these I shall subjoin short
explanations, containing the best and most simple means of procuring the different
species of acids, and some account of the general properties of the neutral salts they
produce.
I shall not deny that to render this work more complete, it would have been
necessary to add particular observations upon each species of salt, its solubility in water
and alcohol, the proportions of acid and of salifiable base in its composition, the quantity
of its water of crystallization, the different degrees of saturation it is susceptible of, and,
finally, the degree of force or affinity with which the acid adheres to the base. This
immense work has been already begun by Messrs. Bergman, Morveau, Kirwan, and other
celebrated chemists, but is hitherto only in a moderate state of advancement, even the
principles upon which it is founded are not perhaps sufficiently accurate.
These numerous details would have swelled this elementary treatise to much too
great a size; besides that, to have gathered the necessary materials, and to have completed
all the series of experiments requisite, must have retarded the publication of this book for
many years. This is a vast field for employing the zeal and abilities of young chemists,
whom I would advise to endeavor rather to do well than to do much, and to ascertain, in
the first place, the composition of the acids, before entering upon that of the neutral salts.
Every edifice which is intended to resist the ravages of time should be built upon a sure
foundation; and, in the present state of chemistry, to attempt discoveries by experiments,
either not perfectly exact, or not sufficiently rigorous, will serve only to interrupt its
progress, instead of contributing to its advancement.
5 There is yet a third degree of oxygenation of acids, as the oxygenated muriatic and oxygenated nitric
acids. The terms applicable to the neutral salts resulting from the union of these acids with salifiable bases
is supplied by the Author in the Second Part of this Work. These are formed by prefixing the word
oxygenated to the name of the salt produced by the second degree of oxygenation. Thus, oxygenated muriat
of potash, oxygenated nitrat of soda, &c.—Translator.
118
Notes on the Reading
1. You may also want to compare your results from burning the sulfur in Demonstration 6
with those Lavoisier describes on p. 101.
2. You have seen the great emphasis Lavoisier places on the weights being equal before and
after a reaction. This is apparent in his memoirs and in the portions of the Elements of
Chemistry that you read. Also consider the following quotations from Chapter XIII of the
Elements of Chemistry:
We may lay it down as an incontestable axiom that in all the operations of art and
nature nothing is created; an equal quantity of matter exists both before and after the
experiment ; the quality and quantity of the elements remain precisely the same; and
nothing takes place beyond changes and modifications in the combination of these
elements. Upon this principle the whole art of performing chemical experiments
depends . We must always suppose an exact equality between the elements of the
body examined and those of the products of its analysis.
We may consider the substances submitted to fermentation, and the products
resulting from that operation, as forming an algebraic equation; and, by successively
supposing each of the elements in this equation unknown, we can calculate their
values in succession, and thus verify our experiments by calculation, and our
calculation by experiment reciprocally. I have often successfully employed this
method for correcting the first results of my experiments, and to direct me in the
proper road for repeating them to advantage.
Note the references to “algebra”: All this supports the view that he held to a Law of
Conservation of Matter. How would you state this law? What evidence can you cite in
support of it? Later we will be writing chemical “equations” (in analogy to algebraic
equations), and as with algebraic equations we may not “lose” anything. All chemical
equations imply a conservation of mass. For now we will write word equations (rather
than symbol equations). Such equations will be a major concern in the sophomore
natural science. Our task is to unpack their meaning.
3. A table of the kind mentioned in the last line of Chapter VIII will be found on the next
page.
4. Why does Lavoisier refer to a salt as a “secondary order of combination” (p. 109)?
5. Compare Lavoisier's criteria for what is an acid, a salifiable base, and a salt with your
criteria in your lab.
119
120
On the “Acidifying Principle”
Lavoisier seems to have been the first to propose that a single element is present as a
component in all acids, and is responsible for their characteristic properties (Elements of
Chemistry, p. 102). Can you think of any information available to him that might lead to
questioning the hypothesis that oxygen is the “acidifying principle”?
In support of Lavoisier’s assumption that degree of oxygenation is involved in
determining acidity, we may cite the following facts: Sulfuric acid is more strongly acidic
in its properties than sulfurous acid and phosphoric acid is more acidic than phosphorous
acid. Also, in the case of metals such as manganese, chromium, and tungsten, it is found
that the more highly oxygenated oxides form acids and the less highly oxygenated oxides
form what we now call bases.
The crucial question is obviously whether all acids contain oxygen. Where
Lavoisier is unable to show that a particular acid contains oxygen, he assumes that the
“radical” or “base” of the acid has not yet been dissociated from oxygen. Of the 48 acids
that he lists as known to him (Elements of Chemistry, pp. 114-115), the large majority
were known to contain oxygen. In the years 1810-1815, however, chemists reached the
conclusion that a number of the common acids do not contain oxygen. Among these are
muriatic (our hydrochloric) and fluoric (our hydrofluoric) acids. The theory that oxygen
is the acidifying principle was therefore abandoned.
Let us examine briefly the case of muriatic acid. It is obtained by heating sea salt
with sulfuric acid (see Elements of Chemistry, p. 104). A colorless gas with a sharp odor
comes off. This in turn dissolves readily in water. The resulting solution has all the
typically acidic properties.
In 1774 Carl Wilhelm Scheele had already found that, when muriatic acid is
added to a certain oxide of manganese, there is evolved a greenish-yellow gas with an
irritating odor. He called the gas dephlogisticated muriatic acid. Then in 1785, Claude
Berthollet, believing it to be a compound of the muriatic radical with oxygen, renamed it
oxygenated muriatic acid. This is the name that Lavoisier used (Elements of Chemistry, p.
105). It was finally given its present name of “chlorine” (from the Greek
[chloros], meaning “greenish-yellow”) by Humphry Davy in 1811, who had
come to the conclusion that the gas was an element.
Davy showed that chlorine and hydrogen react together when ignited or when
placed in sunlight to form the same colorless gas that is formed by the reaction of sulfuric
acid on sea salt. In particular, he showed that the water vapor which previous
investigators had always found among the products of this reaction could be eliminated
by properly drying the reactants. Moreover, he showed that many metals react either with
the muriatic acid gas or with its aqueous solution, replacing the hydrogen in the
compound and yielding a chloride salt of the metal—the same salt as was obtained in
many cases by the direct action of chlorine on the metal.1 When an electric current22 was
passed through a concentrated solution of muriatic acid in water, chlorine was released at
1 This is of course what we saw in Experiment 4, Part 1.
2 We will consider the decomposition of some substances by an electric current in Chapter VI, and you will
consider in detail the nature of electricity itself in Senior Natural Science.
121
the wire where the current entered the solution, and hydrogen at the wire where the
current left the solution. All these experiments, and others, indicate that hydrogen and
chlorine are components of muriatic acid, and persuaded Davy that chlorine was an
element and not, say, an oxide of some as of yet unknown substance. From the definition
of “element” given by Lavoisier (Elements of Chemistry, p. 60) it must be clear that,
whereas one can show definitely that some pure substances are composite, there is no
similar possibility of demonstrating that a pure substance is an element. But every
method thought of for decomposing chlorine failed. Therefore it seems that not all acids
contain oxygen.
Is there any other element or substance that might constitute the “acidifying
principle” of acids? A case can be made for hydrogen,3 as follows:
(a) Non-metallic oxides such as those of sulfur, phosphorous, and carbon exhibit
typical acidic properties (sour taste, effect on litmus paper, reaction with certain metallic
oxides to produce salts, etc.) only when water is present. Can you cite your own
experimental evidence in support of this claim? Thus, the possibility arises that these
oxides react with the water to form composites that contain not only oxygen but also
hydrogen—since water contains both.
(b) All acids, including both the “oxyacids” like phosphoric and sulfuric, and the
“hydracids” like hydrochloric, react with such metals as zinc and iron to produce
hydrogen. Is this assertion congruent with your observations in Experiment 4? In
addition, quantitative studies show that the amount of acid decreases in these reactions. A
salt of the metal is formed in its place. It is in fact the same salt that formed by reaction of
the metallic oxides with the acid. (Recall how a phlogistonist would explain how the
same salt could be formed in those two different ways.) The salt shares with the acids that
subset of properties of all chlorides. It is a plausible assumption that the metal has simply
replaced the hydrogen of the acid, and that hydrogen is responsible for the acidic
properties of acids.
On this view, it becomes necessary to revise Lavoisier’s terminology, and to
speak of the oxides of phosphorous, sulfur and carbon not as acids but as acidic
anhydrides (acids minus water). The case with bases is analogous. Metal oxides
themselves do not seem to exhibit basic properties (at least those properties we have used
for identifying bases), but in the presence of water many do exhibit basic properties. Thus
we might consider metal oxides as basic anhydrides. Can you cite experimental evidence
in support of this claim? The metal oxides (basic anhydrides) which dissolved in or
combined with water produced what are called metal hydroxides.
Evaluate the damage, if any, done to Lavoisier’s system by the change in the
“acidifying principle” discussed above.
There is an objection to the assertion that hydrogen is the acidifying principle.
Many substances that contain hydrogen, for instance, grain alcohol and sugar, are not
acidic. Why this is so will be left unexplained for the present. At least it seems to be the
case that all acids are hydrogen-bearing compounds, though perhaps not vice versa. We
might speculate that there must be more than one way for hydrogen to be present in
composite substances, but without much more evidence at this time this will have to
remain merely a speculation. In Chapter VIII we will consider some evidence that will
support this speculation.
3 Davy, and later Pierre Dulong, proposed the hydrogen-theory of acids.
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APPENDIX TO CHAPTER II:
St. Thomas Aquinas on Change of Density [Optional Reading to be read after Lavoisier, Elements of Chemistry, Chapters I and II]
(Commentary on the Physics, book 4, lect. 14, nn. 545, and 552-556 [a selection from
the comments on Physics, IV, 9, 217a21-b11]; translation by C. Decaen)
545. Dicit ergo primo quod quidam
philosophi fuerunt, qui opinati sunt quod
vacuum sit in corporibus, accipientes
rationem ex raro et denso. Videbatur enim
eis quod rarefactio et condensatio fieret
propter vacuum intrinsecum corporibus. Si
vero non esset sic rarum et densum, dicebant
quod non erat possibile ut partes alicuius
corporis coirent, idest subintrarent ad
invicem, et quod aliquod corpus calcaretur,
idest comprimeretur per condensationem…
552. Deinde cum dicit: “Nos autem dicimus
etc.,” solvit praemissam rationem. Tota
autem vis praemissae rationis in hoc
consistit, quod rarefactio et condensatio fiat
per vacuum. Unde hic obviat Aristoteles
ostendens quod contingit rarefieri et
condensari sine vacuo.
554. …et cum aer multus existens reducitur
ad minorem quantitatem per
condensationem, vel ex minori in maiorem
per rarefactionem, eadem materia est quae fit
utrumque in actu, scilicet magnum et
parvum, prius existens ad haec in potentia.
Non ergo condensatio fit per hoc quod
aliquae aliae partes subintrando adveniant;
vel rarefactio per hoc quod partes
inhaerentes extrahantur, ut existimabant
ponentes vacuum inter corpora; sed per hoc
quod materia earundem partium accipit nunc
maiorem, nunc minorem quantitatem, ut sic
rarefieri nihil aliud sit, quam materiam
recipere maiores dimensiones per
reductionem de potentia in actum;
condensari autem e converso. Sicut autem
materia est in potentia ad determinatas
formas, ita etiam est in potentia ad
determinatam quantitatem. Unde rarefactio
et condensatio non procedit in rebus
naturalibus in infinitum.
545. He says, therefore, that there were some
philosophers who thought that there is a vacuum
within bodies, taking an argument from the rare and
the dense. For it appeared to them that rarefaction
and condensation occur on account of a vacuum
intrinsic to bodies. In truth, if the rare and the dense
were not thus, they said that it would not be possible
that parts of any body could contract, i.e., steal
inward toward each other, and that any body be
compressed, i.e., be pressed together, through
condensation…
552. Next, when he says, “We, however, say, etc.,”
he resolves the aforesaid argument. The whole
power of the aforesaid argument consists in this,
that rarefaction and condensation come to be [only]
through a vacuum. Whence Aristotle opposes this,
showing that something can be rarefied and
condensed without a vacuum.
554. …[W]hen much existing air is reduced to a
lesser quantity through condensation, or from the
lesser to the greater through rarefaction, it is the
same matter that becomes each in act (namely, great
and small), existing before in potency with respect
to these.
Therefore condensation does not come to be
through this, that certain other parts come to it by
steeling inward, nor does rarefaction come to be
through this, that inhering parts are drawn outward,
as some think, positing a vacuum among the bodies.
Rather, [it happens] through this: that the matter of
the same parts takes now a greater, now a lesser
quantity, such that being rarefied is nothing other
than matter receiving greater dimensions through a
reduction from potency into act, and being
condensed is the converse. However, just as matter
is in potency to determinate forms, so also it is in
potency to a determinate quantity. Whence in
natural things rarefaction and condensation do not
proceed into infinity.
123
CHAPTER III
Further Developments in the New Chemistry: Weight Laws
Claude Louis Berthollet
Selections from
Essay on Chemical Statics (1803)1
INTRODUCTION
1. The powers which produce chemical phenomena are all derived from the
mutual attraction of the molecules2 of bodies. The name affinity has been given to this
mutual attraction to distinguish it from astronomical [gravitational] attraction.
It is probable that the two are the same property. Astronomical attraction,
however, is exercised only between masses placed at a distance, where the shape of the
molecules, the spaces within them, and their particular attributes have no influence. Its
effects, always proportional to the mass and to the inverse of the square of the distances,
can be rigorously submitted to calculation. The effects of chemical attraction, or affinity,
are on the contrary so altered by particular conditions, often indeterminate, that they
cannot be deduced from a universal principle; rather, they must be determined one by
one. Only some of these effects can be sufficiently separated from other phenomena so as
to admit of the precision of calculation.
Thus only observations can establish the chemical properties of bodies, or the
affinities by which they engage in mutual action under definite conditions. However,
since it is very probable that affinity does not differ in its origin from general attraction, it
should equally be subject to the laws that mechanics has determined for phenomena
which are caused by the action of mass.3 For the same reason, it is natural to think that the
1 [Translated in by Joseph & Caroline Haggarty from C. L. Berthollet, Essai de statique chimique, Vols. I
& II (Paris: Firmin Didot, 1803).]
2 [It would be premature to assume that Berthollet—or, for that matter, any of the chemists we read until
Avogadro in Chapter VII—intends by “molecule” precisely the same notion as that entailed by the atomic
theory we have today. Indeed, the original meaning of the word is “little bulk,” or “tiny mass” (from moles
and the diminuitive –icula).]
3 [In 1801 Berthollet published a book entitled Researches into the Laws of Affinity which presented
experimental evidence that chemical affinity was not absolute, but was dependent on the quantity or mass
of the chemicals exerting the action: “I propose to prove that elective affinities do not act as absolute forces
by virtue of which one substance in a combination would be displaced by some other. Instead, in all
compositions and decompositions caused by elective affinity, the object of the combination [A] is divided
between the substances [B and C] whose actions are opposed, and the proportions of this division are
determined not only by the strength of the affinity of these substances, but also by the quantity with which
124
more universal the principles reached by chemical theory, the more analogous to
mechanical principles they will be. But only by the path of observation can chemical
principles reach that degree of universality which we can already point out.
The immediate effect of a substance’s affinity is always a combination; thus all
the effects produced by chemical action are a consequence of the formation of some
combination.
Every substance which has a tendency to enter into combination acts by reason of
its affinity and its quantity. These truths form the ultimate term to which all chemical
observations resolve.
Two points must be observed, however.
First: In order to explain the phenomena which they produce, or to compare them
to each other, one must regard different tendencies to combination as so many forces
which contribute to one result, or which, by their opposition, destroy one other.
Second: A substance’s chemical action does not depend solely on the affinity and
the quantity of the parts which compose it. It also depends on the state of these parts—
whether due to their present combination, their affinity is concealed to a greater or lesser
degree, or due to their expansion or contraction, their mutual distance varies. These are
the conditions which, by modifying the properties of the elementary parts of a substance,
form what I call its constitution. In order to arrive at the analysis of a chemical action,
one must take into account not only each one of these conditions, but even more, the
circumstances to which they are in some way related….
The universal law governing chemical action—that substances act by virtue of
their affinity and quantity—is modified in its effects not only by cohesive force, but also
by the expansive action of caloric, i.e., of the cause of heat, which is the principle of
expansibility….
All natural phenomena take place in the atmosphere, which often contributes to
their generation by its force of compression, by its temperature, or by the combination of
the parts composing it. It is therefore necessary to have an accurate knowledge of the
qualities of the atmosphere in these three respects.
The result of the different factors which intervene during chemical action is
sometimes a combination whose proportions are constant. Sometimes, by contrast, the
proportions of the combinations which are formed are not fixed, but vary according to the
circumstances in which they are produced. The first case requires that the accumulation
of those forces which would change the proportions be equal to those which tend to
maintain the present state of combination. But when this obstacle is overcome, chemical
action continues to produce its proper effect by reason of the strength of the affinities and
of the quantities of the substances which exercise them. I have attempted to ascertain the
conditions which thus limit the proportions in some combinations and which seem to
interrupt the process of chemical action….
they act. Thus the quantity can compensate for the strength of the affinity so as to produce the same degree
of saturation. If I establish that the quantity of a substance can compensate for the strength of its affinity, it
will follow that a substance’s action is proportional to the quantity of it necessary to produce a certain
degree of saturation. I call that quantity which is the measure of the capacity of different substances to
effect saturation their [active] mass.”
125
ON COMBINATION
36. In the preceding chapters, I first considered the effects of the mutual affinity
which produces the cohesion of molecules, and then those which arise from the action
opposed to the cohesive force and from the liquid which tends towards the destruction of
that force. But all chemical action between two different substances produces an effect
analogous to that caused by the mutual affinity of similar molecules: such action forms,
or tends to form, a union among them which is the product of their mutual affinity and
which varies according to the strength of this action and according to the resistance
against it. To this union of two substances, as well as to the act which produces it, is
given the name combination.
From this it follows that a solution is a true combination, and that its action, even
at its weakest, is due to the same cause. The only difference between a solution and a
combination in the ordinary sense concerns the aspect under which each is considered. In
the case of a solution, one attends principally to the liquidity which a solid body acquires
through combination, and above all to the uniformity of the parts of the composite liquid;
the same applies to a gaseous solution. In the case of combination in the ordinary sense,
one attends principally to the other properties of the composite which has been formed—
properties which result from the union of its elements—by comparing them to those
which belonged to the substances which combined. In most cases, the solution is merely
due to a weak combination which has not caused the characteristic properties of the
dissolved body to disappear.
One consequence of the preceding considerations is that, in combination, we are
bound to discover the same laws which we have observed in the chemical action which
produces solution….
38. If we consider what is observed in the mutual combination of two antagonistic
substances—an acid and an alkali, for example—we find that the acidity diminishes in
proportion as the quantity of the alkali increases, and there arises a degree of saturation in
which the acidity and alkalinity have both disappeared and become latent. If, however,
one continues to add alkali, its character reappears and becomes more and more
dominant.
One therefore sees, first, that acidity and alkalinity saturate each other and can
become alternately dominant according to the proportion in which the combination
occurs. Moreover, there is no impediment, no pause in the progress of the combination
and of the saturation which accompanies it—unless the cohesive force or elasticity
produce a separation4 in which there appear proportions fixed by one of these two
conditions.
And secondly, one sees that the acidic and alkaline properties diminish according
to the degree of the saturation undergone by the acid and the alkali, such that one
discovers in the most intense chemical action the same characteristics which we observed
in a very weak degree when a solution is produced.
4 [The precipitation of an insoluble solid or the effervescence of a gas.]
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39. Chemists, struck by the fact that they find definite proportions in many
combinations, have often regarded it as a universal property of combinations that they are
constituted in constant proportions. Thus they hold that, when a neutral salt receives an
excess of an acid or of an alkali, the homogenous substance which results is a solution of
neutral salt in a free portion of the acid or alkali.
This is an hypothesis whose only foundation is a distinction between solution and
combination—a hypothesis in which the properties which cause a separation are confused
with the affinity which produces a combination. One must, however, recognize the
circumstances which can determine that combinations will separate5 in a certain state,
and which thereby set limits to the effects of the general law of affinity.
It is not always at the term of neutralization that separation can come into effect.
The acid tartrate of potash separates and crystallizes more easily than the neutral tartrate
does: are we to say that it is the latter which is held in solution by the excess acid?6 I
believe that I can limit myself to this example for the moment.
40. In consequence of what has just been set forth, it is necessary to distinguish
two kinds of saturation. The first is the limit of the chemical action which one substance
can engage in with another under the given circumstances: for example, one says that the
water is saturated with a salt when it cannot dissolve any more of it, even though neither
the properties of salt nor those of water have undergone saturation. The other kind of
saturation is the term at which the antagonistic properties of a substance have been
disguised by one another, and have reached an equilibrium which produces a state of
indifferenence called neutralization. This second kind of saturation is rarely encountered
at the same point as the first….
42. Several points follow from the foregoing. The first is that chemical action, the
strongest as well as the weakest, is exerted by reason of the mutual affinity of the
substances and by reason of their quantities found in the sphere of activity. The second is
that chemical action diminishes on account of saturation. The third is that there is no
point at which chemical action causes fixed proportions; it is instead in the forces which
oppose chemical action that one must seek the limits of its power and the limits of the
proportions of the combinations formed by it. The final point is that two effects of
chemical action must be distinguished: that by which it produces mutual saturation, and
that which brings about changes in constitution.
ASSORTED PASSAGES
ON SEPARATION AND THE PROPORTIONS OF ELEMENTS IN VARIOUS COMBINATIONS
193. …An interesting problem remains to be solved: namely, to identify the
dispositions and the circumstances which determine that the proportions are fixed in
certain combinations, while in others they occur in all proportions…
5 [Circumstances that cause the precipitation of solid or the effervescence of a gas.]
6 [When tartaric acid is halfway toward neutralization with potash, the material which is most readily
crystallized out of solution is called acid tartrate of potash. It is less soluble in water than tartaric acid
completely neutralized by potash (tartrate of potash).]
127
196. The cause of the separation of a substance which has entered the solid state is
therefore the same as the cause of the proportions with which it separates. These
proportions are those with which the cohesive force has strength sufficient for producing
separation, and they must be constant when the circumstances are the same…
197. Since the force by which a combination is formed produces a condensation,
and thereby increases the effects of the mutual action [of the elements in the
combination], these effects will occur especially at the term of saturation, where the two
elements of the combination exert the greatest degree of their power, as long as they
possess an equal disposition to solidity7 . . . In those combinations whose elements appear
to have nearly equal dispositions to solidity, like the salts whose base is soda, potash, or
ammoniac, and whose acid is muriatic, nitric, or acetic, the greatest degree of
concentration should therefore be at the term of neutralization….It is thus in the neutral
state that combinations whose elements have a nearly equal disposition [to solidity]8
separate through crystallization because this is the point at which their condensation is
the greatest….
194. [A] solid, a salt for example, dissolves in water in all proportions up to the
extreme point which yields saturation, where the dissolving force finds itself weaker than
the cohesive force opposed to it. But the level of saturation varies according to
temperature, which diminishes the resistance caused by cohesion…
Metals which fuse into alloys dissolve in all proportions when the difference
between their densities and fusibilities does not interrupt this mutual dissolution…
Substances which form glass also combine in all proportions up to the extreme
point where the insolubility of some of them and the temperature present an obstacle to
the formation of this solution which, being uniform and transparent, has all of the
characteristics of a chemical combination wherein all properties have become
common….
373. Many chemists, struck by the fixed points to which some oxidations are
limited, suppose that there are always definite degrees to which combination with oxygen
must submit. They ascribe to nature a balance which, subject to their own decrees,
determines the proportions which combinations must take. And they do so without
paying the least attention to the circumstances in which one can discover the causes
which limit the action of substances that tend to combine—causes whose influence
theoretical considerations oblige us to evaluate….
I must therefore show the following points. First, that the proportions of oxygen
in the oxides depends on the same conditions which influence the other combinations.
Secondly, that these proportions can vary progressively from the point at which the
combination becomes possible up to that at which it attains the ultimate degree. Thirdly,
that when this does not occur, it is merely because the conditions which I have identified
present an obstacle to this progressive action.
7 [That is, insolubility.]
8 [Such as the aforementioned neutral salts.]
128
Joseph Louis Proust
Researches on Copper1
On Carbonate of Copper
One hundred pounds of copper, dissolved in sulfuric or nitric acid and precipitated by the
carbonate of soda or potash, invariably gives 180 pounds of green carbonate.2 If this
quantity is submitted to a gradual distillation it gives 10 pounds of water, which appears
as essential to the color and composition of this carbonate as the carbonic acid itself,
since this water only passes over successively and conjointly with the acid. Deprived of
these two components the carbonate leaves 125 pounds of black oxide at the bottom of
the retort. This oxide dissolves in nitric acid with heat without decomposing the acid.
Likewise it dissolves in oxidized muriatic acid, from which, then, the oxygen escapes in
bubbles, since copper is unable to combine with more than 25 parts of oxygen per 100.
One may, then, in all analyses take 180 pounds of carbonate or 125 pounds of black oxide
for 100 pounds of copper. Native carbonates of copper are also found in this ratio of
oxidation.
Here are the components of the artificial carbonate:
Copper . . . . . . . . . . . . .100
Oxygen . . . . . . . . . . . . . 25
Carbonic Acid . . . . . . . .46
Water . . . . . . . . . . . . . . .10
180 [sic] . . .
On Native Carbonate of Copper
If 100 parts of this carbonate, dissolved in nitric acid and separated by the alkaline
carbonates, gives us 100 parts of artificial carbonate, and if the base of these two
combinations is the black oxide, we must recognize that invisible hand that holds the
balance for us in the formation of compounds and fashions properties according to its
will. We must conclude that nature operates not otherwise in the depths of the world than
at its surface or in the hands of man. These ever-invariable proportions, these constant
attributes, which characterize true compounds of art or of nature, in a word, this pondus
naturae so well seen by Stahl; all this, I say, is no more at the power of the chemist than
the law of election that presides at all combinations. From these considerations is it not
right to believe that the native carbonate of copper will never differ from that which art
produces in its imitation? Is there actually any difference between native carbonate of
soda and the natural? No. Why, therefore, should there be any difference between those
of copper or of other metals when no other perturbing cause has disarranged the
1 [Ann. Chim. (1799), 32: 26-54.]
2 [Green copper carbonate is also known as malachite.]
129
reciprocal forces of the factors of these combinations?
The malachites of Aragon in nitric acid lose carbonic acid and leave one-
hundredth part of sandy clay. By precipitation we reproduce 99 parts of artificial
carbonate in which we discover scarcely a grain of calcareous carbonate. This solution,
made warm, never shows any nitrous gas, which proves well that copper completely
refuses further oxidation.
One hundred grains of the same, calcined in a crucible at a moderate temperature
leaves 71 grains of black oxide. If we now subtract from this 2 parts for 100 of foreign
earth, we have 69 to express the oxide contained in the malachite; but, differing only by a
small fraction, these 69 grains correspond to 99 of artificial carbonate. There is, then, no
difference between these two oxides, and in nature, as in art, the degree of their oxidation
is evidently the same . . .
The following extracts are from later papers by Proust.]
But if it is found that in our hands metals cannot bind oxygen beyond the fixed
ratios known to us, because the progress of their oxidation is suddenly checked by the
action of the opposing forces specified by Berthollet, shall we also be obliged to believe
that when nature does not proceed beyond these very same ratios in the oxides that she
offers us, this is because her resources for oxidation are limited by the very same
opposing forces as those that prevail in our laboratories? And yet this is what would have
to be granted in order to account for the constant agreement we find between the
composition and properties of nature’s oxide and ours. This, I hold, involves an identity
of causes that it will not be found easy to admit; on the contrary, we shall rather concur in
the belief that the combinations that we make every day in our laboratories have a perfect
resemblance to those of nature; this is due to the fact that the powers of nature hold
invisible sway over all the operations of our arts. If we find it impossible to make an
ounce of nitric acid, an oxide, a sulfide, or a drop of water, in ratios other than those that
nature had assigned to them from all eternity, we must again recognize that there is a
balance that, subject to the decrees of nature, regulates even in our laboratories the
ratios of compounds. And even if some day we should succeed in clearly recognizing the
causes that retard or accelerate the action of substances tending to combine, we could
only flatter ourselves with knowing one more thing, namely, the means that nature uses to
restrict compounds to the ratios in which we find them combined. But such knowledge,
would it invalidate the principle I have proved? I think not, because the principle is only
the corollary of the facts that we discover every day; there is nothing hypothetical about
it; facts have led to it, facts alone can overthrow it . . .
[Note: Berthollet believed that when mercury is dissolved in nitric acid under varying conditions
of concentration and temperature, a variety of nitrates corresponding to a large number of
different oxides is produced. But he had to explain why these nitrates, when treated with
hydrochloric acid, always gave a mixture of only two salts, or chlorides, of fixed composition: the
insoluble calomel (mercurous chloride) and the soluble corrosive sublimate (mercuric chloride).]
To remove this difficulty, Berthollet says that the mercury passes into two
130
compounds of constant composition only at the moment when it can separate in these two
combinations. Hence it would have to be assumed that, in mixing the muriatic acid with
the nitrate, these two combinations are only formed at the precise moment when the
separation of the soluble and the insoluble salts is initiated by the action of this acid. That
is to say, the numerous oxides that in Berthollet’s opinion give rise to as many different
nitrates all present in the same solution, urged by the affinity of muriatic acid as much as
by the insolubility of one of the chlorides about to be formed—these oxides, I say,
suddenly and simultaneously abandon the positions they had occupied in the series, to
rush to its two extreme values, to place themselves just where are found the corrosive
sublimate and the calomel, the only two compounds remaining after the operation. It
must be admitted that this is a case of oxides behaving with much intelligence. . . If by
raising the temperature we reduce the rate of an oxide that had reached the highest degree
of oxidation, and that does not suffer the inconvenience of being volatile; or on the other
hand, if by long-continued heating we raise a metal to this highest stage of oxidation, will
it be permissible to believe with good reason that all the ascending and descending terms
of oxidation, which by these means we can introduce between the extremes, represent as
many different oxides? Certainly not! I will not recognize in this the ordinary course of
nature. I do believe that in such cases we produce mixtures in all possible ratios, of the
oxide at the minimum with the oxide at the maximum . . .
[A second citation, concerning the difference between compounds and mixtures, follows. It is
taken from Journal de physique 63: 369 (1806).]
But what difference, it will be asked, do you recognize between your chemical
combinations and the unions of combinations, which latter you tell us nature restricts to
no fixed ratios?
Is the power that makes a metal dissolve in sulfur different from that which makes
one metallic sulfide dissolve in another? I shall be in no hurry to answer this question,
legitimate though it be, for fear of losing myself in a region not yet sufficiently lighted up
by the science of facts. But my distinctions will, I hope, be appreciated all the same when
I say: Is the attraction that makes sugar dissolve in water the same or not the same as that
which makes a determinate quantity of carbon and hydrogen dissolve in another quantity
of oxygen to form the sugar3 of our plants? But that which we see clearly is that these two
sorts of attractions are so different in their results that it is impossible to confound them.
Thus the solution of niter in water is, for me, not at all like of that of azote in
oxygen that produces nitric acid or that of nitric acid in potash that produces saltpeter.4
The solution of ammonia in water is to my eyes not at all like that of hydrogen in
azote that produces ammonia . . .
Sulfide of antimony can dissolve in the lower oxide in an infinite number of ratios
3 [Sugar was known at this time to be composed of carbon, hydrogen, and oxygen. In Experiment 1 we
observed the decomposition of sugar into carbon and water (which is composed of hydrogen and oxygen).]
4 [Saltpeter, another name for niter, is a salt commonly found to exude from rocks (whence its name); its
chemical name is potassium nitrate, and was so named because it was commonly prepared from potash and
nitric acid.]
131
that give rise to the livers, the glasses, the crocuses, and all the intermediate shades. But
is it so with the antimony itself in its relations to sulfur? Do we know of solutions of the
one substance in the other of two sulfides of antimony? In the unions termed
“compounds,” nature imposes laws on itself and us, so that no chemist can make
compounds in new proportions. Chemistry no longer confounds these two types of union,
but needs names to distinguish them.
Questions and Problems
1. If you still have a copy of your class results for Experiment 2, consider what relevance
they may have to the dispute between Berthollet and Proust.
2. If one accepts Proust’s position as the more defensible, what does it add to the science of
“affinities” of which Lavoisier confessed ignorance (Elements of Chemistry, p. 59)?
3. In the writing of chemical equations, what has Proust added to the Lavoisierian
equations?
4. Proust speaks of two sorts of attractions among substances (p. 130). Can you distinguish
these?
5. Does Proust’s evidence speak to all or only to some of the objections that Berthollet
raises against asserting constant composition in composite substances?
6. Henceforth we will refer to the constant composition (of two or more elements) of pure
substances as compounds. Among the substances referred to by Proust on the bottom of
p. 130 and top of p. 131, can you decide which are compounds? How should we describe
the other substances?
7. Berthollet seems to accept the constant composition of substances that precipitate out of
solutions. Is this sufficient to satisfy Proust’s assertion that there are constant-
composition substances?
8. When table salt in water is heated, water is driven off and table salt remains. When
mercuric oxide is heated, oxygen is driven off and mercury remains. Saltwater is said to
be a solution; mercuric oxide is said to be a compound. On what grounds is this
distinction justified?
9. Are you able to compose an operational definition of a compound?
* * * * *
132
Jeremias Benjamin Richter
Extract from Rudiments of Stoichiometry1
Mathematics includes all those sciences that refer to magnitude, and consequently a
science lies more or less in the province of mathematics (geometry), according as it
requires the determination of magnitudes. In chemical experiments this truth has often led
me to the question, whether and how far chemistry is a part of applied mathematics; and
especially in considering the well-known fact that two neutral salts, when they
decompose each other, form again neutral compounds. The immediate consequence, in
my opinion, could only be that there are definite relations between the magnitudes of the
component parts of neutral salts. From that time I considered how these proportions could
be made out, partly by exact chemical experiments, partly combining chemical with
mathematical analysis. In my inaugural dissertation, published at Königsberg, in 1789, I
made a slight attempt, but was not then supplied with the requisite chemical apparatus,
nor was I sufficiently ready with all the requisite information, bearing on my present
system, imperfect as it may be. The result, therefore, was very imperfect. I promised,
however, not to let the matter rest with that imperfect essay, but to work out this branch
with the accuracy and profundity of which I was capable, as soon as I was supplied with
the requisite conveniences. This promise, I hope in the present volume, to make good,
although I am far from believing that what I am now going to say will not be in need of
still more thorough and accurate elaboration, for who will venture to limit the extent and
power that is the destination of a young and budding science? . . .
[A]s the mathematical portion of chemistry deals in a great measure with bodies
that are either elements or substances incapable of being decomposed, and as it teaches
also their relative magnitudes, I have been able to find no more fitting name for this
scientific discipline than the word stoichiometry, from (stoicheion), which in
the Greek language means a something that cannot be divided, and (metrein),
which means to find out relative magnitudes . . .
1 [Anfangsgründe der Stöchyometrie oder Messkunst chymischer Elemente, vol. 1, Preface, published 1792-
1794.]
133
DEFINITION 12
Stoichiometry is the science of measuring the quantitative proportions, or the proportions
of the masses in which chemical elements stand in regard to each other. The mere
knowledge of these relations might be called quantitative stoichiology . . .
Principle 1
Every infinitely small particle of the mass of an element has an infinitely small part of the
chemical attractive force of affinity . . .
EXPERIENCE 5
In order to make a neutral compound out of two elements, it is needful, as each of the
elements is of the same constitution at one time as at another, to take the same quantity
for the first part formed as for the second part. For example, if two parts of lime require
five parts of muriatic acid for solution, six parts of lime will require fifteen of the same
acid.
EXPERIENCE 6
When two neutral solutions are mixed, and a decomposition follows, the new resulting
products are almost without exception neutral also, but if the solutions of one or both are
not neutral before mixing, the products after mixture are also not neutral.
Corollary 1
The elements must therefore have amongst themselves a certain fixed proportion of mass.
To determine which, their neutral compounds generally give the best opportunity.3
Corollary 2
If the weights of the masses of two neutral compounds that decompose each other are A
and B, and the mass of the one element in A is a, and that of the one in B is b, then the
masses of the elements in A are A – a and a, and those in B are B – b and b. The
proportions of the masses of the elements in the neutral compounds before decomposition
are A – a : a and B – b : b; but after decomposition the new products are a + B – b and b
+ A – a, and the proportion of the masses of the elements is a : B – b, and b : A – a. If the
proportion of the masses in the compounds A and B is known, that in the new products is
known also.
If a + B – b = C and b + A – a = D, then a = C + b – B = b + A – D and C – B = A
– D, so also D – B = A – C. In addition, b = a + B – C = D – A + a. . . .
2 [Ibid., Vol. 1, pp. 121 ff.]
3 There is present in the element a certain subjectum to which the chemical attractive power or the affinity
is bound; this is the mass of the element.
134
[The following is a French translation of a table of Richter’s equivalents taken from Berthollet’s
Essai de Statique Chimique, Paris, 1803, Vol. I, p. 136. The numbers represent the weight units of
each substance listed that are equivalent to (i.e., would saturate/neutralize) 1000 weight units of
sulfuric acid. Richter considered all the bases listed to be elements. In this he follows Lavoisier.
Bases
Alumina . . . . . . . . . . . 525
Magnesia . . . . . . . . . . 615
Ammoniac . . . . . . . . . 672
Lime . . . . . . . . . . . . . . 793
Soda . . . . . . . . . . . . . 859
Strontia . . . . . . . . … 1329
Potash . . . . . . . . . . . 1605
Barytes . . . . . . . . . . 2222
Acids
Fluoric . . . . . . . . . . .427
Carbonic . . . . . . . . . 577
Sebacic . . . . . . . . . . 706
Muriatic . . . . . . . . . 712
Oxalic . . . . . . . . . . 755
Phosphoric . . . . . . . 979
Formic . . . . . . . . . . 988
Sulfuric . . . . . . . . 1000
Succinic . . . . . . . . 1209
Nitric . . . . . . . . . . 1405
Acetic . . . . . . . . . . 1480
Citric . . . . . . . . . . 1683
Tartarous . . . . . . . 1694
135
CHAPTER IV
Atoms Proposed
John Dalton
Extracts from
A New System of Chemical Philosophy1
Chapter 2: On the Constitution of Bodies
There are three distinctions in the kinds of bodies, or three states, which have more especially
claimed the attention of philosophical chemists: namely, those that are marked by the terms
elastic fluids, liquids, and solids. A very familiar instance is exhibited to us in water, of a body
which, in certain circumstances, is capable of assuming all three states. In steam we recognize a
perfectly elastic fluid, in water, a perfect liquid, and in ice, a complete solid. These observations
have tacitly led to the conclusion that seems universally adopted that all bodies of sensible
magnitude, whether liquid or solid, are constituted of a vast number of extremely small particles,
or atoms2 of matter, bound together by a force of attraction, which is more or less powerful
according to circumstances, and which, as it endeavors to prevent their separation, is very
properly called in that view attraction of cohesion; but as it collects them from a dispersed state
(as from steam into water) it is called attraction of aggregation, or more simply, affinity.
Whatever names it may go by, they still signify one and the same power. It is not my design to
call in question this conclusion, which appears completely satisfactory, but to show that we have
hitherto made no use of it, and that the consequence of the neglect has been a very obscure view
of chemical agency, which is daily growing more so in proportion to the new lights attempted to
be thrown upon it.
The opinions I more particularly allude to are those of Berthollet on the Laws of chemical
affinity, such as that chemical agency is proportional to the mass, and that in all chemical unions
there exist insensible gradations in the proportions of the constituent principles. The
inconsistence of these opinions, both with reason and observation, cannot, I think, fail to strike
everyone who takes a proper view of the phenomena.
Whether the ultimate particles of a body, such as water, are all alike, that is, of the same
figure, weight, &c., is a question of some importance. From what is known, we have no reason to
apprehend a diversity in these particulars: If it does exist in water, it must equally exist in the
elements constituting water, namely, hydrogen and oxygen. Now it is scarcely possible to
conceive how the aggregates of dissimilar particles should be so uniformly the same. If some of
1 [From A New System of Chemical Philosophy (Manchester, England: 1808), Part I, pp. 141-143.]
2 [“Atom” is a transliteration of the Greek word (atomos), meaning “uncut,” or “indivisible.”]
136
the particles of water were heavier than others, if a parcel of the liquid on any occasion were
constituted principally of these heavier particles, it must be supposed to affect the specific gravity
of the mass, a circumstance not known. Similar observations may be made on other substances.
Therefore we may conclude that the ultimate particles of all homogeneous bodies are perfectly
alike in weight, figure, &c. In other words, every particle of water is like every other particle of
water; every particle of hydrogen is like every other particle of hydrogen, &c. . . .
Chapter 3: On Chemical Synthesis3
When any body exists in the elastic state, its ultimate particles are separated from each other to a
much greater distance than in any other state; each particle occupies the center of a comparatively
large sphere, and supports its dignity by keeping all the rest, which by their gravity or otherwise
are disposed to encroach upon it, at a respectful distance. When we attempt to conceive the
number of particles in an atmosphere, it is somewhat like attempting to conceive the number of
stars in the universe; we are confounded with the thought. But if we limit the subject, by taking a
given volume of any gas, we seem persuaded that, let the divisions be ever so minute, the number
of particles must be finite; just as in a given space of the universe, the number of stars and planets
cannot be infinite.
Chemical analysis and synthesis go no farther than to the separation of particles one from
another, and to their reunion. No new creation or destruction of matter is within the reach of
chemical agency. We might as well attempt to introduce a new planet into the solar system, or to
annihilate one already in existence, as to create or destroy a particle of hydrogen. All the changes
we can produce consist in separating particles that are in a state of cohesion or combination, and
joining those that were previously at a distance.
In all chemical investigations it has justly been considered an important object to
ascertain the relative weights of the simples that constitute a compound. But unfortunately the
enquiry has terminated here; whereas from the relative weights in the mass, the relative weights
of the ultimate particles or atoms of the bodies might have been inferred, from which their
number and weight in various other compounds would appear, in order to assist and to guide
future investigations, and to correct their results. Now it is one great object of this work to show
the importance and advantage of ascertaining the relative weights of the ultimate particles, both
of simple and compound bodies, the number of simple elementary particles that constitute one
compound particle, and the number of less compound particles that enter into the formation of
one more compound particle.
If there are two bodies, A and B, which are disposed to combine, the following is the
order in which the combinations may take place, beginning with the most simple: namely,
3 [A New System of Chemical Philosophy, pp. 211-216 and 219-220.]
137
1 atom of A + 1 atom of B = 1 atom of C, binary.4
1 atom of A + 2 atoms of B = 1 atom of D, ternary.
2 atoms of A + 1 atom of B = 1 atom of E, ternary.
1 atom of A + 3 atoms of B = 1 atom of F, quaternary.
3 atoms of A + 1 atom of B = 1 atom of G, quaternary. &c
The following general rules may be adopted as guides in all our investigations respecting
chemical synthesis.
1st. When only one combination of two bodies can be obtained, it must be presumed to be
a binary one, unless some cause appear to the contrary.
2d. When two combinations are observed, they must be presumed to be a binary and a
ternary.
3d. When three combinations are obtained, we may expect one to be a binary, and the
other two ternary.
4th. When four combinations are observed, we should expect one binary, two ternary,
and one quaternary, &c.
5th. A binary compound should always be specifically heavier than the mere mixture of
its two ingredients.
6th. A ternary compound should be specifically heavier than the mixture of a binary and
a simple, which would, if combined, constitute it; &c.
7th. The above rules and observations usually apply when two bodies, such as C and D,
D and E, &c., are combined.
From the application of these rules to the chemical facts already well ascertained, we
deduce the following conclusions: 1st. That water is a binary compound of hydrogen and oxygen,
and the relative weights of the two elementary atoms are as 1 : 7, nearly; 2d. That ammonia is a
binary compound of hydrogen and azote, the relative weights of the two atoms are as 1 : 5,
nearly; 3d. That nitrous gas is a binary compound of azote and oxygen, the atoms of which weigh
5 and 7 respectively, that nitric acid is a binary or ternary compound according as it is derived,
and consists of one atom of azote and two of oxygen, together weighing 19; that nitrous oxide is
a compound similar to nitric acid, and consists of one atom of oxygen and two of azote, weighing
17; that nitrous acid is a binary compound of nitric acid and nitrous gas, weighing 31; that
oxynitric acid is a binary compound of nitric acid and oxygen, weighing 26; 4th. That carbonic
oxide is a binary compound, consisting of one atom of charcoal, and one of oxygen, together
weighing nearly 12; that carbonic acid is a ternary compound (but sometimes binary) consisting
4 [Dalton elsewhere explains his language of speaking of a binary “atom”:
I have chosen the word atom to signify those ultimate particles in preference to particle, molecule, or any other
diminutive term because I conceive it is much more expressive; it includes in itself the notion of indivisible,
which the other terms do not. It may, perhaps, be said that I extend the application of it too far when I speak of
compound atoms; for instance, I call an ultimate particle of carbonic acid a compound atom. Now, though this
atom may be divided, yet it ceases to become carbonic acid, being resolved by such division into charcoal and
oxygen. Hence I conceive there is no inconsistency in speaking of compound atoms and that my meaning cannot
be misunderstood. (Dalton’s Manuscript Notes, Royal Institution Lecture 18, January 30, 1810.)]
138
of one atom of charcoal, and two of oxygen, weighing 19; &c. In all these cases the weights are
expressed in atoms of hydrogen, each of which is denoted by unity.
In the sequel, the facts and experiments from which these conclusions are derived, will be
detailed, as well as a great variety of others from which are inferred the constitution and weight
of the ultimate particles of the principal acids, the alkalis, the earths, the metals, the metallic
oxides and sulfurets, the long train of neutral salts, and in short, all the chemical compounds that
have hitherto obtained a tolerably good analysis. Several of the conclusions will be supported by
original experiments.
From the novelty as well as importance of the ideas suggested in this chapter, it is deemed
expedient to give plates, exhibiting the mode of combination in some of the more simple cases. A
specimen of these accompanies this first part. The elements or atoms of such bodies as are
conceived at present to be simple are denoted by a small circle with some distinctive mark, and
the combinations consist in the juxtaposition of two or more of these; when three or more
particles of elastic fluids are combined together in one, it is to be supposed that the particles of
the same kind repel each other, and therefore take their stations accordingly.
PLATE IV. This plate contains the arbitrary marks or signs chosen to represent the
several chemical elements or ultimate particles.
ELEMENTS
Simple
1. Hydrogen its rel. weight 1
2. Azote 5
3. Carbone or charcoal 5
4. Oxygen 7
5. Phosphorus 9
6. Sulfur 13
7. Magnesia 20
8. Lime 23
9. Soda 28
10. Potash 42
139
11. Strontites 46
12. Barytes 68
13. Iron 38
14. Zinc 56
15. Copper 56
16. Lead 95
17. Silver 100
18. Platina 100
19. Gold 140
20. Mercury 167
Binary
21. An atom of water or steam, composed of 1 of oxygen and 1 of hydrogen,
retained in physical contact by a strong affinity, and supposed to be surrounded by a
common atmosphere of heat, its relative weight = 8.
22. An atom of ammonia, composed of 1 of azote and 1 of hydrogen = 6.
23. An atom of nitrous gas, composed of 1 of azote and 1 of oxygen = 12.
24. An atom of olefiant gas, composed of 1 of carbone and 1 of hydrogen = 6.
25. An atom of carbonic oxide composed of 1 of carbone and 1 of oxygen = 12.
Ternary
26. An atom of nitrous oxide, 2 azote + 1 oxygen = 17.
27. An atom of nitric acid, 1 azote + 2 oxygen = 19.
140
28. An atom of carbonic acid, 1 carbone + 2 oxygen = 19.
29. An atom of carburretted hydrogen, 1 carbone + 2 hydrogen = 7.
Quaternary
30. An atom of oxynitric acid, 1 azote + 3 oxygen = 26.
31. An atom of sulfuric acid, 1 sulfur + 3 oxygen = 34.
32. An atom of sulfuretted hydrogen, 1 sulfur + 3 hydrogen = 16.
33. An atom of alcohol, 3 carbone + 1 hydrogen = 16.
Quinquenary
34. An atom of nitrous acid, 1 nitric acid + 1 nitrous gas = 31.
Sextenary
35. An atom of acetous acid, 2 carbone + 2 water = 26.
Septenary
36. An atom of nitrate of ammonia, 1 nitric acid + 1 ammonia + 1 water = 33.
37. An atom of sugar, 1 alcohol + 1 carbonic acid = 35.
Enough has been given to show the method; it will be quite unnecessary to devise
characters and combinations of them to exhibit to view in this way all the subjects that come
under investigation; nor is it necessary to insist upon the accuracy of all these compounds, both
141
in number and weight; the principle will be entered into more particularly hereafter, as far as
respects the individual results. It is not to be understood that all those articles marked as simple
substances are necessarily such by the theory; they are only necessarily of such weights. Soda
and Potash, such as they are found in combination with acids, are 28 and 42 respectively in
weight; but according to Mr. Davy’s very important discoveries, they are metallic oxides; the
former then must be considered as composed of an atom of metal, 21, and one of oxygen, 7; and
the latter, of an atom of metal, 35, and one of oxygen, 7. Or, soda contains 75 per cent. metal and
25 oxygen; potash, 83.3 metal and 16.7 oxygen. It is particularly remarkable that, according to
the above-mentioned gentleman’s essay on the Decomposition and Composition of the fixed
alkalis, in the Philosophical Transactions (a copy of which essay he has just favored me with), it
appears that “the largest quantity of oxygen indicated by these experiments was, for potash 17,
and for soda, 26 parts in 100, and the smallest 13 and 19.”
* * * * *
Questions and Problems:
1. Dalton’s atomic symbols allow us to write chemical equations without using words. Balanced
equations are those with the same numbers of each kind of atom on each side of the equation.
Write balanced equations, using these symbols, for the compounds: water, nitrous gas, and
nitrous acid. Under each symbol or aggregate of symbols indicate the relative weight represented
by the number of atoms you have indicated. Appreciate that a balanced “atomic” equation is an
assertion about the relative weights of reactiving substances and their products.
2. What is your judgment of Dalton’s rules?
3. How does Dalton determine the number and weights of the atoms contained in the compounds he
discusses in the paragraph on the bottom of p. 137 and top of p. 138?
4. There are two common oxides of carbon known by weight. If one accepts Dalton’s rule #2, how
does one determine whether the two common oxides of
carbon are a) or b)?
(The latter pair is, of course, Dalton’s conclusion.)
5. The law of multiple proportions is demonstrated,
among other compounds, by the two common oxides
of carbon: 6 g of carbon may combine with 8 g of oxygen to form one common oxide, or with 16
g of oxygen to form another. Besides the two common oxides of carbon, there is a third oxide of
carbon known, although it is difficult to prepare. In this oxide, 6 g of carbon combines with 12 g
of oxygen. This seems to indicate that one atom of carbon combines with 1 ½ atoms of oxygen!
Can you reconcile the existence of this compound with Dalton’s atomic theory? (Here we have
used the preferred modern atomic weights instead of Dalton’s.)
6. Why does Dalton suppose that “the particles of the same kind repel each other”?
142
Joseph Louis Gay-Lussac
Memoir on the Combination of Gaseous Substances With Each Other1
Substances, whether in the solid, liquid, or gaseous state, possess properties that are
independent of the force of cohesion; but they also possess others that appear to be modified by
this force (so variable in its intensity), and that no longer follow any regular law. The same
pressure applied to all solid or liquid substances would produce a diminution of volume differing
in each case, while it would be equal for all elastic fluids. Similarly, heat expands all substances;
but the dilatations of liquids and solids have hitherto presented no regularity, and it is only those
of elastic fluids which are equal and independent of the nature of each gas. The attraction of the
molecules in solids and liquids is, therefore, the cause that modifies their special properties; and
it appears that it is only when the attraction is entirely destroyed, as in gases, that bodies under
similar conditions obey simple and regular laws. At least, it is my intention to make known some
new properties in gases, the effects of which are regular, by showing that these substances
combine amongst themselves in very simple proportions, and that the contraction of volume that
they experience on combination also follows a regular law. I hope by this means to give a proof
of an idea advanced by several very distinguished chemists—that we are perhaps not far removed
from the time when we shall be able to submit the bulk of chemical phenomena to calculation.
It is a very important question in itself, and one much discussed amongst chemists, to
ascertain if compounds are formed in all sorts of proportions. Mr. Proust, who appears first to
have fixed his attention on this subject, is of the opinion that the metals are susceptible of only
two degrees of oxidation, a minimum and a maximum; but led away by this seductive theory, he
has seen himself forced to entertain principles contrary to physics in order to reduce to two
oxides all those that the same metal sometimes presents. Mr. Berthollet thinks, on the other
hand—reasoning from general considerations and his own experiments—that compounds are
always formed in very variable proportions, unless they are determined by special causes, such as
crystallization, insolubility, or elasticity. Lastly, Dalton has advanced the idea that compounds of
two bodies are formed in such a way that one atom of one unites with one, two, three, or more
atoms of the other.2 It would follow from this mode of looking at compounds that they are
formed in constant proportions, the existence of intermediate bodies being excluded, and in this
respect Dalton’s theory would resemble that of Mr. Proust; but Mr. Berthollet has already
strongly opposed it in the Introduction he has written to Thomson’s Chemistry, and we shall see
that in reality it is not entirely exact. Such is the state of the question now under discussion; it is
still very far from receiving its solution, but I hope that the facts that I now proceed to set forth,
facts that had entirely escaped the notice of chemists, will contribute to its elucidation.
Suspecting, from the exact ratio of 100 of oxygen to 200 of hydrogen,3 which Mr. Humboldt
1 [“Mémoire sur la combinaison des substances gazeuses les unes avec les autre,” Mémoires de la Société d’Arcueil
2 (1809), pp. 207-234.]
2 Dalton has been led to this idea by systematic considerations; and one may see from his work, A New System of
Chemical Philosophy, p. 213, and from that of Thomson, Vol. 6, that his researches have no connection with mine. 3 [The ratio given is that of combining volumes. In this paper, combining ratios are generally given by volume,
143
and I had determined for the proportions of water, that other gases might also combine in simple
ratios, I have made the following experiments. I prepared fluoboric,4 muriatic, and carbonic
gases, and made them combine successively with ammonia gas. 100 parts of muriatic gas5
saturate precisely 100 parts of ammonia gas, and the salt that is formed from them is perfectly
neutral, whether one or other of the gases is in excess. Fluoboric gas, on the contrary, unites in
two proportions with ammonia gas. When the acid6 gas is put first into the graduated tube, and
the other gas is then passed in, it is found that equal volumes of the two condense, and that the
salt formed is neutral. But if we begin by first putting the ammonia gas into the tube, and then
admitting the fluoboric gas in single bubbles, the first gas will then be in excess with regard to
the second, and there will result a salt with excess of base, composed of 100 of fluoboric gas and
200 of ammonia gas. If carbonic gas7 is brought into contact with ammonia gas by passing it
sometimes first, sometimes second into the tube, there is always formed a sub-carbonate8
composed of 100 parts of carbonic gas and 200 of ammonia gas. It may, however, be proved that
neutral carbonate of ammonia would be composed of equal volumes of each of these
components. Mr. Berthollet, who has analyzed this salt, obtained by passing carbonic gas into the
sub-carbonate, found that it was composed of 73.34 parts by weight of carbonic gas and 26.66 of
ammonia gas. Now, if we suppose it to be composed of equal volumes of its components, we
find from their known specific gravity that it contains by weight:9
71.81 of carbonic acid.
28.19 of ammonia,
100.0
a proportion differing only slightly from the preceding.
If the neutral carbonate of ammonia could be formed by the mixture of carbonic gas and
ammonia gas, as much of one gas as of the other would be absorbed; and since we can only
obtain it through the intervention of water, we must conclude that it is the affinity of this liquid
that competes with that of the ammonia to overcome the elasticity of the carbonic acid, and that
the neutral carbonate of ammonia can only exist through the medium of water.
Thus we may conclude that muriatic, fluoboric, and carbonic acids take exactly their own
unless specifically identified as “by weight.”]
4 Mr. Thenard and I have given the name of fluoboric gas to that particular gas which we obtained by distilling pure
fluoride of lime with vitreous boracic acid.
5 [“Muriatic gas” is muriatic acid gas.]
6 [“Alkaline” is in the original.]
7 [“Carbonic gas,” here and throughout the paper, is carbonic acid gas.]
8 [“Sub-carbonate”: Lavoisier called the neutral salt formed by carbonic acid and ammoniac the “carbonate” of
ammoniac. But Gay-Lussac describes a non-neutral salt of these two substances in which the acid is deficient. Since
this salt contains a smaller proportion of carbonic acid than does the neutral carbonate, it is called a sub-carbonate.]
9 [Gay-Lussac has elsewhere accepted the following specific weights (air = unity): carbonic acid gas 1.5193;
ammonia gas 0.59642. If equal volumes of these combine to form the sub-salt, their combining weights must be to
one another as their specific weights. Of a total of 100 parts, then, 71.81 and 28.19 are those that will be to one
another as 1.5193 is to 0.59642.]
144
volume of ammonia gas to form neutral salts, and that the last two take twice as much to form
sub-salts. It is very remarkable to see acids so different from one another neutralize a volume
of ammonia gas equal to their own; and from this we may suspect that if all acids and all
alkalies could be obtained in the gaseous state, neutrality would result from the combination of
equal volumes of acid and alkali.10
It is not less remarkable that, whether we obtain a neutral salt or a sub-salt, their elements
combine in simple ratios that may be considered as limits to their proportions. Accordingly, if we
accept the specific gravity of muriatic gas determined by Mr. Biot and myself,11 and those of
carbonic gas and ammonia given by Mssrs. Biot and Arago, we find that dry muriate of ammonia
is composed [by weight] of:
Ammonia 100.0 38.35
or
Muriatic acid 160.7 61.65
100.00
a proportion very far from that of Mr. Berthollet:
100 of ammonia,
213 of acid.
In same way, we find that the sub-carbonate of ammonia contains:
Ammonia, 100.0 43.98
or
Carbonic acid, 127.3 56.02
100.00
And the neutral carbonate:
Ammonia, 100.00 28.19
or
Carbonic acid, 254.6 71.81
100.00
It is easy from the preceding results to ascertain the ratios of the capacity of fluoboric,
muriatic, and carbonic acids; for since these three gases saturate the same volume of ammonia
gas, their relative capacities will be inversely as their densities, allowance having been made for
the water contained in muriatic acid.
We might even now conclude that gases combine with each other in very simple ratios; but I
shall still give some fresh proofs.
10
[Gay-Lussac’s speculation, if borne out, would certainly provide a welcome basis for the understanding of
“neutral” salts. Nevertheless, it is not true that neutral salts are always formed by quantities of acid and alkali which,
if gaseous, would occupy equal volumes—as we will see later, in Avogadro’s work.]
11
As muriatic acid contains one-fourth its weight of water, we must only take three-fourths of the density for that of
real muriatic acid. [Note that Gay-Lussac still accepts Lavoisier’s oxygen theory of acids, so he believes the muriatic
acid contains oxygen. In experimental work a few years after publishing this paper Gay-Lussac provided evidence
that some acids do not contain oxygen, thus weakening Lavoisier’s theory of the acidifying principle.]
145
According to the experiments of Mr. Amédée Berthollet, ammonia is composed of:
100 of nitrogen,
300 of hydrogen, by volume.
I have found (1st. vol. of the Societe d'Arcueil) that sulfuric acid is composed of:
100 of sulfurous gas,
50 of oxygen gas.
When a mixture of 50 parts of oxygen and 100 of carbonic oxide12 (formed by the distillation
of oxide of zinc with strongly calcined charcoal) is inflamed, these two gases are destroyed and
their place taken by 100 parts of carbonic acid gas. Consequently carbonic acid may be
considered as being composed of:
100 of carbonic oxide gas,
50 of oxygen gas.
Davy, from the analysis of various compounds of nitrogen with oxygen, has found the
following proportions by weight:
Nitrogen Oxygen
Nitrous oxide 63.30 36.70
Nitrous gas 44.05 55.95
Nitric acid 29.50 70.50
Reducing these proportions to volumes, we find:
Nitrogen Oxygen
Nitrous oxide 100 49.5
Nitrous gas 100 108.9
Nitric acid 100 204.7
The first and the last of these proportions differ only slightly from 100 to 50, and 100 to 200;
it is only the second that diverges somewhat from 100 to 100. The difference, however, is not
very great, and is such as we might expect in experiments of this sort; and I have assured myself
that it is actually nil. On burning the new combustible substance from potash13 in 100 parts by
volume of nitrous gas, there remained over exactly 50 parts of nitrogen, the weight of which,
deducted from that of the nitrous gas (determined with great care by Mr. Berard at Arcueil),
yields as result that this gas is composed of equal parts by volume of nitrogen with oxygen:
Nitrogen Oxygen
Nitrous oxide 100 50
Nitrous gas 100 100
Nitric acid 100 200
From my experiments, which differ very little from those of Mr. Chenevix, oxygenated
muriatic acid is composed by weight of:
Oxygen 22.92
Muriatic acid 77.08
12
[The “carbonic oxide” referred to is the first oxide of carbon, which is now called “carbon monoxide.” In what
follows he will refer to the second oxide of carbon as “carbonic gas” and “carbonic acid,” which is now called
“carbon dioxide.”]
13
[This substance was discovered by Davy and is now called “potassium.” We will read of Davy’s experiment in
Chapter VI.]
146
Converting these quantities into volumes, we find that oxygenated muriatic acid14 is formed of:
Muriatic gas 300.0
Oxygen gas 103.2
a proportion very nearly:
Muriatic gas 300
Oxygen gas 100
Thus it appears evident to me that gases always combine in the simplest proportions when
they act on one another; and we have seen in reality in all the preceding examples that the ratio of
combination is 1 to 1, 1 to 2, or 1 to 3. It is very important to observe that in considering weights
there is no simple and finite relation between the elements of any one compound; it is only when
there is a second compound between the same elements that the new proportion of the element
that has been added is a multiple of the first quantity. Gases, on the contrary, in whatever
proportions they may combine, always give rise to compounds whose elements by volume are
multiples of each other.
Not only, however, do gases combine in very simple proportions, as we have just seen, but
the apparent contraction of volume that they experience on combination has also a simple relation
to the volume of the gases, or at least to one of them.
I have said, following Mr. Berthollet, that 100 parts of carbonic oxide gas, prepared by
distilling oxide of zinc and strongly calcined charcoal, produce 100 parts of carbonic gas on
combining with 50 of oxygen. It follows from this that the apparent contraction of the two gases
is precisely equal to the volume of oxygen gas added.15 The density of carbonic gas is thus equal
to that of carbonic oxide plus half the density of oxygen gas;16 or, conversely, the density of
carbonic oxide gas is equal to that of carbonic gas, minus half that of oxygen gas. Accordingly,
taking the density of air as unity, we find the density of carbonic oxide gas to be 0.9678, instead
of 0.9569 experimentally determined by Cruickshanks.17 We know, besides, that a given volume
of oxygen produces an equal volume of carbonic acid; consequently, oxygen gas doubles its
volume on forming carbonic oxide gas with carbon, and so does carbonic gas on being passed
over red-hot charcoal. Since oxygen produces an equal volume of carbonic gas, and the density
of the latter is well known, it is easy to calculate the proportion of its elements. In this way we
find that carbonic gas is composed [by weight] of:
27.38 of carbon,
72.62 of oxygen,
and carbonic oxide of:
42.99 of carbon,
14
[See footnote 11.]
15
[A total of 150 parts of carbonic oxide and oxygen produce only 100 parts by volume of carbonic gas. Thus the
two combining gases have apparently contracted their total volume by 50 parts—an amount equal to the initial
volume of the oxygen.]
16
[This relation among densities is easier to deduce if we restate the proportions of the gases as follows: “1 volume
of carbonic acid gas is the product of 1 volume of carbonic oxide gas combined with ½ volume of oxygen gas.”]
17
[Since Gay-Lussac regards the densities of oxygen and carbonic acid gas as well-established, he can use the
previous relation to calculate a more reliable value for the density of carbonic oxide gas.]
147
57.01 of oxygen
Pursuing a similar course, we find that if sulfur takes 100 parts of oxygen to produce
sulfurous acid, it takes 150 parts to produce sulfuric acid. As a matter of fact, we find that
sulfuric acid, according to the experiments of Mssrs. Klaproth, Bucholz, and Richter, is
composed of 100 parts by weight of sulfur and 138 of oxygen.
On the other hand, sulfuric acid is composed of 2 parts by volume of sulfurous gas, and 1
of oxygen gas. Consequently, the weight of a certain quantity of sulfuric acid should be the same
as that of 2 parts of sulfurous acid and 1 of oxygen gas, i.e., 2 x 2.265, plus 1.10359 = 5.63359,
seeing that, according to Kirwan, sulfurous gas weighs 2.265, the density of air being taken as
unity. But from the proportion of 100 of sulfur to 138 of oxygen, this quantity contains 3.26653
of oxygen, and if we subtract from it 1.10359 there will remain 2.16294 for the weight of oxygen
in 2 parts of sulfurous acid, or 1.08147 for the weight of oxygen contained in 1 part.
Now, as this last quantity only differs by 2 percent from 1.10359, which represents the
weight of 1 part of oxygen gas, it must be concluded that oxygen gas, in combining with sulfur to
form sulfurous gas, only experiences a diminution of a fiftieth of its volume, and this would
probably be nil if the data I have employed were more exact. On this last supposition, using
Kirwan’s value for the specific gravity of sulfurous gas, we should find that this acid is
composed of:
100.00 of sulfur,
95.02 of oxygen.
But if, adopting the preceding proportions for sulfuric acid, we allow, as appears probable, that
100 of sulfurous gas contain 100 of oxygen gas, and that 50 have still to be added to convert it
into sulfuric acid, [it will be]:
100.00 of sulfur
92.0 of oxygen.
Its specific gravity, calculated on the same suppositions, and referred to that of air, would be
2.30314, instead of 2.2650 as Kirwan found directly.18
Phosphorus is very closely connected with sulfur, seeing that both have nearly the same
specific gravity. Consequently phosphorous should take up twice as much oxygen to become
phosphorous acid, as to pass from this state into phosphoric acid. Since the latter is composed,
according to Rose, of:
100.0 of phosphorus,
114.0 of oxygen,
it follows that phosphorous acid should contain:
100.0 phosphorus,
76.0 of oxygen.
18
In order to remove these differences it would be necessary to make new experiments on the density of sulfurous
gas, on the direct union of oxygen gas with sulfur to see if there is contraction, and on the union of sulfurous gas
with ammonia gas. I have found, it is true, on heating cinnabar in oxygen gas, that 100 parts of this gas only produce
93 of sulfurous gas. It also appeared as if less sulfurous gas than ammonia gas was necessary to form a neutral salt.
But as these experiments have not been done in suitable conditions—especially the last, which could only be made
in presence of water, the sulfurous gas decomposing and precipitating sulfur immediately on being mixed with the
ammonia gas—I intend to repeat them and to determine exactly all the conditions before drawing any conclusion
from them. This is all the more necessary, as sulfurous gas can be used to analyze sulfuretted hydrogen gas, if its
proportions are well known.
148
We have seen that 100 parts of nitrogen gas take 50 parts of oxygen gas to form nitrous
oxide, and 100 of oxygen gas to form nitrous gas. In the first case, the contraction is a little
greater than the volume of oxygen added; for the specific gravity of nitrous oxide, calculated on
this hypothesis, is 1.52092, while that given by Davy is 1.61414. But it is easy to show, from
some of Davy’s experiments, that the apparent contraction is precisely equal to the volume of
oxygen gas added. On passing the electric spark through a mixture of 100 parts of hydrogen and
97.5 of nitrous oxide, the hydrogen is destroyed and 102 parts of nitrogen remain, including that
quantity that is almost always mixed with the hydrogen, and a little of the latter gas that has
escaped combustion. The residue, after making all corrections, would be very nearly equal in
volume to the nitrous oxide employed. Similarly, on passing the electric spark through a mixture
of 100 parts of phosphuretted hydrogen and 250 of nitrous oxide, water and phosphoric acid are
formed, and exactly 250 parts of nitrogen remain—another evident proof that the apparent
contraction of the elements of nitrous oxide is equal to the whole volume of oxygen added.
From this circumstance, its specific gravity referred to that of air should be 1.52092.
The apparent contraction of the elements of nitrous gas appears, on the other hand, to be
nil. If we admit, as I have shown, that it is composed of equal parts of oxygen and nitrogen, we
find that its density, calculated on the assumption that there is no contraction, is 1.036, while that
determined directly is 1.038.
Saussure found that the density of water vapor is to that of air as 10 is to 14. Assuming
that the contraction of volume of the two gases is only equal to the whole volume of oxygen
added, we find instead of this a ratio of 10 to 16. This difference, and the authority of a physicist
so distinguished as Saussure, would seem to be enough to make us reject the assumption I have
just made; but I shall mention several circumstances that render it very probable. First, it has a
very strong analogy in its favor; secondly, Mr. Trales found by direct experiment that the ratio of
the density of the water vapor to air is 10 to 14.5, instead of 10 to 14; thirdly, although we do not
know very exactly the volume occupied by water on passing into the elastic state, we do know,
from the experiments of Watt, that a cubic inch of water produces very nearly a cubic foot of
steam, i.e., a volume 1728 times as great. Now, adopting Saussure’s ratio, we find only 1488 for
the volume occupied by water when it is converted into steam; but adopting the ratio of 10 to 16,
we should have 1700.6. Finally, the refraction of water vapor, calculated on the assumption of
the ratio 10 to 14, is a little greater than the observed refraction; but that calculated from the ratio
of 10 to 16 is much more in harmony with the results of the experiment. These, then, are the
considerations that go to make the ratio 10 to 16 very probable.
Ammonia gas is composed of three parts by volume of hydrogen and one of nitrogen, and
its density compared to air is 0.596. But if we suppose the apparent contraction to be half of the
whole volume, we find 0.594 for the density. Thus it is proved, by this almost perfect
concordance, that the apparent contraction of its elements is precisely half of the total volume, or
rather double the volume of the nitrogen.
I have already proved that oxygenated muriatic gas is composed of 300 parts of muriatic
gas and 100 of oxygen gas. Admitting that the apparent contraction of the two gases is half the
whole volume, we find 2.468 for its density, and by experiment 2.470. I have also assured myself
by several experiments that the proportions of its elements are such that it forms neutral salts
with the metals. For example, if we pass oxygenated muriatic gas over copper, there is formed a
slightly acid green muriate, and a little oxide of copper is precipitated, because the salt cannot be
obtained perfectly neutral. It follows from this that in all the muriates, as in oxygenated muriatic
149
acid, the acids reduced to volume is thrice the oxygen. It would be the same for carbonates and
fluorides, the acids of which have for equal volumes the same saturation capacity as muriatic
acid.
We see, then, from these various examples, that the contraction experienced by two gases
on combination is in almost exact relation with their volume, or rather with the volume of one of
them. Only very slight differences exist between the densities of compounds obtained by
calculation and those given by experiment, and it is probable that, on undertaking new
researches, we shall see them vanish entirely.
Recalling the great law of chemical affinity, that every combination involves an approx-
imation19 of the elementary particles, it is difficult to conceive why carbonic oxide gas should be
lighter than oxygen.20 Indeed, that is the principal reason that has led Mr. Berthollet to assume the
existence of hydrogen in this gas, and thus explain its low density. But it seems to me that the
difficulty arises from supposing that the approximation of the elementary particles is represented
in gases by the diminution of volume that they suffer on combination.21 This supposition is not
always true, and we might cite several gaseous combinations, the constituent particles of which
would be brought very close together, although there is not only no diminution of volume, but
even a dilatation. Such, for example, is nitrous gas, whether we consider it as being formed
directly from nitrogen and oxygen, or from nitrous oxide and oxygen. In the first case, there is no
diminution of volume;22 and in the second, there would be dilatation, for 100 parts of nitrous
oxide and 50 of oxygen would produce 200 of nitrous gas. We know too that carbonic gas
represents an exactly equal volume of oxygen, and that the affinity that unites its elements is
very powerful. Nevertheless, if we admitted an immediate relation between the condensation of
the elements and the condensation of volume, we should conclude, contrary to experiment, that
there is no condensation. Otherwise it would be necessary to suppose that if carbon were in the
gaseous state it would combine in equal volumes (or in any other proportion) with oxygen, and
that the apparent condensation would then be equal to the whole volume of the gaseous carbon.
But if we make this supposition for carbonic acid, we may also make it for carbonic oxide, by
assuming, for instance, that 100 parts of gaseous carbon would produce 100 parts of the gas on
combining with 50 parts of oxygen. However it may stand with these suppositions, which only
serve to make it conceivable that oxygen can produce a compound lighter than itself by
combining with a solid substance, we must admit, as a truth founded on a great number of
observations, that the condensation of the particles of two combining substances, in particular of
two gases, has no immediate relation to the condensation of volume, since we often see that
whilst one is very great the other is very small or even nil.
The observation that the gaseous combustibles combine with oxygen in the simple ratios
19
“Approximation”: id est, an approach to one another.
20
Oxygen being a constituent of carbonic oxide, how can the whole be lighter than the part? “Lighter,” that is,
volume for volume.
21
[That is, it is a mistake to suppose that any mutual approach of the respective particles of combining gases is
necessarily reflected in a diminution of the volume they afterwards occupy. Note that Gay-Lussac here is rejecting
the “5th Rule” propounded by Dalton.]
22
[Since, as we saw above, 100 volumes of nitrogen and 100 volumes of oxygen yield 200 volumes of nitrous gas.]
150
of 1 to 1, 1 to 2, 1 to ½, can lead us to determine the density of the vapors of combustible
substances, or at least to approximate closely to that determination. For if we suppose all
combustible substances to be in the gaseous state, a specified volume of each would absorb an
equal volume of oxygen, or twice as much, or else half; and as we know the proportion of
oxygen taken up by each combustible substance in the solid or liquid state, it is sufficient to
convert the oxygen into volumes, and also the combustible, under the condition that its vapor
shall be equal to the volume of oxygen, or else double or half this value. For example, mercury is
susceptible of two degrees of oxidation, and we may compare the first one to nitrous oxide. Now
according to Mssrs. Fourcroy and Thenard, 100 parts of mercury absorb 4.16, which reduced to
gas would occupy a space of 8.20. These 100 parts of mercury reduced to vapor should therefore
occupy twice the space, viz., 16.40. We thence conclude that the density of mercury vapor is
12.01 greater than that of oxygen, and that that metal on passing from the liquid to the gaseous
state assumes a volume 961 times as great.
I shall not discuss more of these determinations, because they are only based on
analogies, and it is besides easy to multiply them. I shall conclude this Memoir by examining if
compounds are formed in constant or variable proportions, as the experiments of which I have
just given an account lead me to the discussion of these two opinions.
According to Dalton’s ingenious idea, that combinations are formed from atom to atom,
the various compounds that two substances can form would be produced by the union of one
molecule of the one with one molecule of the other, or with two, or with a greater number, but
always without intermediate compounds. Thomson and Wollaston have indeed described
experiments that appear to confirm this theory. Thomson has found that super-oxalate of potash
contains twice as much acid as is necessary to saturate the alkali; and Wollaston, that the sub-
carbonate of potash contains, on the other hand, twice as much alkali as is necessary to saturate
the acid.
The numerous results I have brought forward in this Memoir are also very favorable to
the theory. But Mr. Berthollet, who thinks that combinations are made continuously, cites in
proof of his opinion the acid sulfates, glass, alloys, mixtures of various liquids—all of which are
compounds with very variable proportions, and he insists principally on the identity of the force
that produces chemical compounds and solutions.
Each of these two opinions has, therefore, a large number of facts in its favor; but
although they are apparently utterly opposed, it is easy to reconcile them.
We must first of all admit, with Mr. Berthollet, that chemical action is exercised
indefinitely in a continuous manner between the molecules of substances, whatever their number
and ratio may be, and that in general we can obtain compounds [composés] with very variable
proportions. But then we must admit at the same time that—apart from insolubility, cohesion,
and elasticity, which tend to produce combinations [combinaisons] in fixed proportions—
chemical action is exerted more powerfully when the elements are in simple ratios or in multiple
proportions among themselves, and that compounds are thus produced that separate out more
easily. In this way we reconcile the two opinions, and maintain the great chemical law, that
whenever two substances are in the presence of each other they act in their sphere of activity
according to their masses, and give rise in general to compounds with very variable proportions,
unless these proportions are determined by special circumstances.
151
Conclusion
I have shown in this Memoir that the combinations of gaseous substances with each other
are always formed in very simple ratios, so that representing one of the terms by unity, the other
is 1, 2, or at most 3. These ratios by volume are not observed with solid or liquid substances, nor
when we consider weights, and they form a new proof that it is only in the gaseous state that
substances are in the same circumstances and obey regular laws. It is remarkable to see that
ammonia gas neutralizes exactly its own volume of gaseous acids; and it is probable that if all
acids and alkalies were in the elastic state, they would all combine in equal volumes to produce
neutral salts. The capacity of saturation of acids and alkalies measured by volume would then be
the same, and this might perhaps be the true manner of determining it. The apparent contraction
of volume suffered by gases upon combining is also very simply related to the volume of one of
them, and this property likewise is peculiar to gaseous substances.
* * * * *
152
APPENDIX TO CHAPTER IV:
Dalton on “On Gay-Lussac’s Laws”1
[Optional Reading]
Some observations on nitric acid, and the other compounds of azote and oxygen, have
been made by Gay-Lussac, in the ad. Vol. of the Mémoires d’ Arcueil. He contends that one
measure of oxygenous gas unites to two measures of nitrous gas to form nitric acid, and to three
measures to form nitrous acid. Now I have shown that 1 measure of oxygen may be combined
with 1.3 of nitrous gas, or with 3.5, or with any intermediate quantity whatever, according to
circumstances, which he seems to allow; what, then, is the nature of the combinations below 2,
and above 3, of nitrous gas? No answer is given to this but the opinions founded upon an
hypothesis that all elastic fluids combine in equal measures, or in measures that have some
simple relation one to the other, as 1 to 2, 1 to 3, 2 to 3, etc. In fact, his notion of measures is
analogous to mine of atoms; and if it could be proved that all elastic fluids have the same number
of atoms in the same volume, or numbers that are as 1, 2, 3, etc., the two hypotheses would be
same, except that mine is universal, and his applies only to elastic fluids. Gay-Lussac could not
but see that a similar hypothesis had been entertained by me, and abandoned as untenable;
however, as he has revived the notion, I shall make a few observations upon it, though I do not
but doubt he will soon see its inadequacy.
Nitrous gas is, according to Gay-Lussac, constituted of equal measures of azote and
oxygen which, when combined, occupy the same volume as when free. He quotes Davy, who
found 44.05 azote, and 55.95 oxygen by weight, in nitrous gas. He converts these into volumes,
and finds them after the rate of 100 azote to 108.9 oxygen, taking the specific gravities according
to Biot and Arago. But that Davy has overrated the oxygen 12 % he shows by burning potassium
in nitrous gas, when 100 measures afforded just 50 of azote. The degree of purity of the nitrous
gas, and the particulars of the experiment, are not mentioned. This one result is to stand against
the mean of three experiments of Davy, and may or may not be more correct, as hereafter shall
appear. Dr. Henry’s analysis of ammonia embraces that of nitrous gas also; he finds 100
measures of ammonia require 120 of nitrous gas for their saturation. Now this will apply to Gay-
Lussac’s theory in a very direct manner; for, according to him, ammonia is formed of 1 measure
of azote and 3 of hydrogen, condensed into a volume of 2; it follows, then, that 100 ammonia
require 75 oxygen to saturate the hydrogen;2 hence 120 nitrous gas should contain 75 oxygen,
instead of 60, or 100 should contain 62.5, instead of 50. Here either the theory of Gay-Lussac or
the experience of Dr. Henry must give results wide of the truth. In regard to ammonia too, it may
further be added, that neither is the ratio of azote to hydrogen 1 to 3, nor is the volume of
ammonia doubled by decomposition, according to the experiments of Berthollet, Davy, and
Henry, made with the most scrupulous attention to accuracy, to which may be added my own.
There is another point of view in which this theory of Gay-Lussac is unfortunate, in
regard to ammonia and nitrous gas: 1 measure of azote with 3 of hydrogen, forms 2 of ammonia;
1 [An appendix to A New System of Chemical Philosophy, part II, published in 1810, pp. 555-559.]
2 [Dalton is assuming that Gay-Lussac will admit that Hydrogen and Oxygen combine in a ratio of 2 : 1, by volume.
Thus, since the volume of the Hydrogen in the 100 measures of Ammonia is 150 (while that of Nitrogen is 50), the
measure of Oxygen that saturates the Hydrogen would be 75.]
153
and 1 measure of azote with 1 of oxygen, forms 2 of nitrous gas; now, according to a well-
established principle in chemistry,3 1 measure of oxygen ought to combine with 3 of hydrogen,
or with one half as much, or twice as much; but no one of these combinations takes place. If
Gay-Lussac adopts my conclusions, namely, that 100 measures of azote require about 250
hydrogen to form ammonia, and that 100 azote require about 120 oxygen to form nitrous gas, he
will perceive that the hydrogen of the former would unite to the oxygen of the latter, and form
water, leaving no excess of either further than the unavoidable errors of experiments might
produce; and thus the great chemical law would be preserved. The truth is, I believe, that gases
do not unite in equal or exact measures in any one instance; when they appear to do so, it is
owing to the inaccuracy of our experiments. In no case, perhaps, is there a nearer approach to
mathematical exactness, than in that of 1 measure of oxygen to 2 of hydrogen; but here, the most
exact experiments I have ever made, gave 1.97 hydrogen to 1 oxygen.
* * * * *
3 [That is, the Law of Equivalents.]
154
155
CHAPTER V
Revisiting the Law of Equivalence
and the Law of Multiple Proportions
William Hyde Wollaston
A Synoptic Scale of Chemical Equivalents1
When the nature of any saline compound is proposed as the subject of inquiry to an
analytic chemist, the questions that occur for his consideration are so varied and so numerous
that he will seldom be disposed to undertake a series of original experiments for the purpose of
satisfying his inquiries, so long as he can rely upon the accuracy of those results that have been
obtained by the labor of others who have preceded him in this field of patient investigation.
If, for instance, the salt under examination be the common blue vitriol, or crystallized
sulfate of copper, the first obvious questions are, (1) How much sulfuric acid does it contain? (2)
How much oxide of copper? (3) How much water? He may not be satisfied with these first steps
in the analysis, but may desire to know further the quantities (4) of sulfur, (5) of copper, (6) of
oxygen, (7) of hydrogen. As a means of gaining this information, he naturally considers the
quantities of various reagents that may be employed for discovering the quantity of sulfuric acid:
(8) how much barytes, (9) carbonate of barytes, or (10) nitrate of barytes would be requisite for
this purpose? (11) How much lead is to be used in the form of (12) nitrate of lead; and when the
precipitate of (13) sulfate of barytes or (14) sulfate of lead are obtained, it will be necessary that
he should also know the proportion that either of them contains of dry sulfuric acid. He may also
endeavor to ascertain the same point by means of (15) the quantity of pure potash, or (16) of
carbonate of potash requisite for the precipitation of the copper. He might also use (17) zinc or
(18) iron for the same purpose, and he may wish to know the quantities of (19) sulfate of zinc, or
(20) sulfate of iron that will then remain in the solution.
These, and very many more questions of the same kind, which it would be tedious to
specify, and needless to enumerate, engage the thoughts, and will occupy much of the time of
every experimental chemist, unless he can have recourse to some record of former analyses on
which he can depend.
The scale, which I am about to describe, is designed to answer at one view all of these
questions, with reference to most of the salts contained in the table, not merely expressing
numerically the proportions by which the desired answers may be calculated, but directly
indicating the actual weights of the several ingredients, contained in any assumed weight of the
salt under consideration, and also the actual quantities of several reagents that may be used, and
of the precipitates that would be obtained by each.
In the formation of this scale, it is requisite in the first place to determine the proportions
in which the different known chemical bodies unite with each other, and to express these
1 [Philosophical Transactions 1814: 1-22 (read to the Royal Society on November 4, 1813).]
156
proportions in such terms that the same substance shall always be represented by the same
number.
It is to Richter that we are originally indebted for this mode of expression, and for having
first observed that law of permanent proportions on which the possibility of this numerical
representation is founded. The proportions assigned to various salts by his predecessors
Bergman, Wenzel, and Kirwan were incompatible with this mode of notation. If we return to
Bergman’s treatise De Analysi Aquarum, we find it stated that in sulfate of potash 40 of acid are
combined with 52 of potash, or that 100 of sulfuric acid take 130 of potash. In muriate of potash,
61 of the alkali are said to be combined with 31 of acid, which is in the proportion of 130 to 66,
so that the same quantity of potash that is saturated by 100 sulfuric acid, requires of muriatic 66.
But if we make a similar estimate by means of lime, since sulfate of lime is said to
contain 46 acid combined with 32 lime, 100 of acid would require 69.5. And in muriate of lime,
since 44 of lime are said to be combined with 31 of acid, thence 69.5 of lime would require 49.
So that in this instance it would appear that the equivalent to 100 sulfuric acid, instead of being
66 muriatic, is 49; which, if true, would defeat our attempts to express the same body always by
the same number.
In comparing the analyses of Wenzel with each other, we find the same inconsistency. If
we select sulfate of ammonia, and muriate of ammonia, we obtain 67.3 as the equivalent of
muriatic acid. But by comparison of sulfate of magnesia with muriate of magnesia, it would
appear to be 73 instead of 67.3.
In referring to the tables of Kirwan, a similar obstacle presents itself to the determination
of the quantity of muriatic acid that is equivalent to a given weight of sulfuric acid. When the
comparison is made by means of potash, the result would make it appear that 68.3 is the relative
weight of muriatic acid. But, if the compounds of these acids with lime be employed in the
computation, the result of 68.3 gives only 59.
Richter remarked, on observing this sort of inconsistency, that if sulfate of potash formed
according to the proportions of Kirwan were decomposed by muriate of lime, there should be
found a large excess of alkali in the solution. But, on the contrary, by direct experiment he found
that neutral salts, when mixed, remained in all cases neutral, and consequently, that the same
weight of muriatic acid would in all cases be found equivalent to the same quantity of sulfuric
acid; and therefore [they] might be conveniently expressed, in stating the compositions of salts,
by the same number. He estimates this acid at 712, as the equivalent to 1000 dry sulfuric acid,
the number assumed as his standard of comparison, to which all other numbers for acids, alkalis,
and earths are adapted.
It could not escape the penetration of Mr. Berthollet, that there exist numerous deviations
from this law of neutralization, and cases of prevailing affinity dependent upon a redundance2 of
one or other ingredient in a mixture of salts. But he was not so happy in detecting the definite
law by which many, at least, of these deviations are governed. It has since been found that when
a base unites with a larger portion of acid than is sufficient to saturate it, the quantity combined
is then an exact simple multiple of the former, thus exhibiting a new modification of the law of
definite proportions, rather than any exception to it.
The first instance in which the same body was supposed to unite with different doses of
2 [That is, a surplus.]
157
another, in such proportions that one of these doses is a simple multiple of the other, was noticed
by Mr. Higgins,3 who conceived, rather than actually observed to occur, certain successive
degrees of oxidation of azote, and represented the series of its combinations with oxygen to be:
Azote 1 with 2 oxygen making nitrous gas.
Azote 1 with 3 oxygen making red nitrous vapor.
Azote 1 with 4 oxygen making yellow nitrous acid.
Azote 1 with 5 oxygen making white nitric acid.
He at the same time added his opinion, that such are the proportions in which these gases
unite to each other by bulk,4 having before observed one instance of union by exactly double bulk
in the formation of water by the combustion of hydrogen and oxygen,5 and expressed his
persuasion that the number of particles in a given bulk of the different gases is the same, and that
the number of particles in the compounds of azote and oxygen are successively in the
proportions above stated.
But though Mr. Higgins, in the instance of the union of hydrogen with oxygen,
anticipated the law of bulks observed by Mr. Gay Lussac, with respect to the union of gases, and
in his conception of union by ultimate particles clearly preceded Mr. Dalton in his atomic views
of chemical combination, he appears not6 to have taken much pains to ascertain the actual
prevalence of that law of multiple proportions by which the atomic theory is best supported, and
it is in fact to Mr. Dalton that we are indebted for the first correct observation of such an instance
of a simple multiple in the union of nitrous gas with oxygen. In his endeavors to determine the
composition of the atmosphere, he found that the quantity of oxygen contained in 100 measures
of common air would combine with either 36 or 72 measures of nitrous gas, according to certain
variations in the mode of conducting the experiment.7
Chemists in general, however, appear to have been by no means duly impressed with the
importance of this observation of Mr. Dalton, till they were in possession of other facts observed
by Dr. Thomson and myself,8 in a more tangible form, with regard to neutral and superacid or
subacid of salts, which could be made the subjects of more deliberate and less equivocal
experiments; and it is, perhaps, owing to the repetition and confirmation of them by Mr.
3 A comparative view of the phlogistic and antiphlogistic theories, 1789, p. 133.
4 [“Bulk” here appears to mean “volume.” On the next page he appears also to mean “volume” when he speaks of
“quantity.”]
5 [In Chapter IV we will read about Gay-Lussac’s discovery pertaining to the combination of gas volumes, and we
will witness a demonstration of the same experiment as that recorded here, but in reverse. Recall that Lavoisier, in
composing water from hydrogen and oxygen gases (Elements of Chemistry, p. 93), mentions that he must use
volumes in a ratio of two to one in order to yield only water. He appears, however, to make nothing of this ratio.]
6 In straw-colored nitrous acid, the proportion appears to be four to one; but the colorless contains about five of
dephloghisticated to one of phlogisticated air. Comparative View, p. 84.
7 Manchester Mem. Vol. V - Nich. Journal, Vol. XIII, p. 433.
8 Phil. Trans. 1808, p. 74. - Ditto, p. 96.
158
Berthollet,9 that they have attracted the attention of other chemists, who are now ready to admit
that the term binacid correctly expresses the relation of many superacid salts to neutrals
consisting of the same ingredients . . . Since that time the additional instances in which the same
law has been observed to prevail are become so numerous, especially with regard to different
degrees of oxidation, that we have the greatest reason to presume that it is universal, and that on
such analyses that are found not to accord with this general observation, we are warranted in
suspecting some degree of inaccuracy in one order or other of the results compared together.
According to Mr. Dalton’s theory, by which these facts are best explained, chemical
union in the state of neutralization takes place between single atoms of the substances combined;
and in cases where there is a redundance of either ingredient, then two or more atoms of this kind
are united to only one of the other.
According to this view, when we estimate the weights of equivalents, Mr. Dalton
conceives that we are estimating the aggregate weights of a given number of atoms, and
consequently the proportion that the ultimate single atoms bear to each other. But since it is
impossible in several instances, where only two combinations of the same ingredients are known,
to discover which of the compounds is to be regarded as consisting of a pair of single atoms, and
since the decision of these questions is purely theoretical, and by no means necessary to the
formation of a table adapted to most practical purposes, I have not been desirous of warping my
numbers according to an atomic theory,10 but have endeavored to make practical convenience my
sole guide, and have considered the doctrine of simple multiples, on which that of atoms is
founded, merely as a valuable assistant in determining, by simple division, the amount of those
quantities that are liable to such definite deviations from the original law of Richter.
Having some time since computed for private use a series of supposed atoms, I had
assumed oxygen as the decimal unit of my scale, in order to facilitate the estimation of those
numerous combinations that it forms with other bodies. But, though in the present table of
Equivalents, I have retained the same unit, and have taken care to make oxygen equally
prominent for the same reason as before, as well as on account of the important part it performs
in determining the affinities of bodies by the different proportions in which it is united to them;
nevertheless the real measure by which most bodies are compared to each other, in any
experiments that I have made, and to which I have, in fact, endeavored to find equivalents, is a
determinate quantity of carbonate of lime. This is a compound that may be regarded as most
distinctly neutral. It is most easy to obtain in a state of uniform purity; most easy to analyze (as a
binary compound); it is a most convenient measure for the powers of acids; and affords the most
distinct expression for the comparative neutralizing powers of alkalis.
Consequently, the first question to be resolved is, by what number are we to express the
relative weight of carbonic acid, if oxygen be fixed at 10. It seems to be very well ascertained
that a given quantity of oxygen yields exactly an equal measure of carbonic acid by union with
carbon; and since the specific gravities of these gases are as 10 to 13.77,11 or as 20 to 27.54, the
9 Mem. D.Arcueil, Tom II, p. 470.
10
[Look, for example, in the Numerical Table of Equivalents, under iron, at the weight of oxygen in the red iron
oxide. What would an atomist make of its weight?]
11
Biot and Arago, 1.1036 : 1.5196 :: 10 : 13.77.
159
weight of carbon may be justly represented by 7.54, which, in this instance, is combined with 2
of oxygen forming the deutoxide, and carbonic oxide being the protoxide will be duly
represented by 17.54.12
Carbonic acid having consequently been assumed as 27.54, it follows from the analysis
of carbonate of lime, which by heat loses 43.7 per cent. of acid, and leaves 56.3 of base, that they
are combined on the proportion of 27.54 to 35.46, and consequently that lime must be
represented by 35.46, and carbonate of lime by 63.
If I would proceed in the series for the purpose of estimating the reliance to be placed on
preceding analyses, I might dissolve 63 of carbonate of lime in muriatic acid, and by evaporating
to perfect dryness should obtain about 69.56 muriate of lime,13 and by deducting the weight of
the lime 35.46 should learn, by means of the difference 34.1, what is to be considered as dry
muriatic acid.
But since lime is now known, by the brilliant discoveries of Sir Henry Davy, to be a
metallic body united with oxygen,14 this salt may also be viewed as a binary compound in a
different light as oxymuriate of calcium; in which case we must transfer the weight of 10 oxygen
to the muriatic acid, making 44.1 of oxymuriatic acid combined with 25.46 calcium. Or, lastly, if
with the same distinguished chemist, we regard it as chloride of calcium, its place in the scale of
equivalents is the same 69.56, and the portion of matter here added to the calcium, whether it
retain its late name of oxymuriatic acid, or revert to its original one of dephlogisticated marine
acid, or assume its new one of chlorine, will be rightly represented by 44.1, which expresses a
bare fact without reference to any theory, and affords the means of estimating the proportion of
this constituent in all muriatic compounds, without need of controversy respecting its simple or
compound nature, which may never admit of any argument that will be deemed conclusive by all
parties.
With the same latitude of interpretation may be understood muriate of potash or of soda
in the scale of equivalents; and the relative weights of mere potash or soda may, perhaps, be
determined better by means of these compounds than by any other, because they are not liable to
be superacid, and are not decomposed by heat.
If to a quantity of muriatic acid, which, by previous trial, I know would dissolve 100 of
carbonate of lime, I add 100 grains of crystallized carbonate of potash, and [with what is left of
the muriatic acid] after the addition find that it will dissolve only 49.8 of carbonate of lime; I
hence infer that 100 of this carbonate [of potash] is equivalent to 50.2 carbonate of lime, and
consequently that 125.5 is the equivalent to 63 in the table.
Next, if I combine 125.5 of crystallized carbonate of potash with an excess of muriatic
acid, and evaporate to dryness, I expel the whole of the water with all redundant acid, and I find
93.2 of neutral salt; and whether I call it muriate of potash, or chloride of potassium, or by any
12
[Deut- and proto- are prefixes from Greek words meaning “second” and “first”; they are analogous to our di- and
mono- prefixes, also from Greek words, but meaning “double” and “single.”]
13
In Dr. Marcet’s experiments on the composition of muriate of lime, referred to in his Analysis of the Water of the
Dead Sea, 50.77 carbonate gave 56.1 of muriate of lime, and 50.77 : 56.1 :: 63 : 69.6.
14
[As Lavoisier anticipated in his Elements of Chemistry, Ch. XVI. The decomposition of lime, soda, and potash
into metals and oxygen will be considered in Chapter VI of this manual.]
160
other name, with any other views, I may deduct 34.1 as dry muriatic acid (whether real or
imaginary15), and infer the equivalent for potash to be 59.1, even though there should, in fact, be
only 49.1 of potassium present, requiring 10 of oxygen16 to convert it into potash.
The next question that occurs relates to the composition of this crystallized carbonate of
potash, which I am induced to call bi-carbonate17 of potash, for the purpose of marking more
decidedly the distinction between this salt and that which is commonly called a subcarbonate,18
and in order to refer at once to the double dose of carbonic acid contained in it. With reference to
carbonate of lime also, I must necessarily consider it as a supercarbonate, for if I add a solution
of this salt to a neutral solution of muriate of lime, a considerable effervescence takes place, from
a redundance of carbonic acid beyond what is necessary to saturate the lime. If I saturate 125.5
of this salt with nitric acid, taking due precautions not to expel any of the fluid along with the gas
that escapes, it loses about 55 of carbonic acid, which is the double of 27.5. But if, previous to
the saturation, I heat the salt moderately red, it loses 38.8, consisting of 27.5 carbonic acid and
11.3 water, after which the addition of an acid expels only 27.5, or a single dose of carbonic
acid.19
I have in this experiment made use of nitric acid in order that the resulting compound
might guide me in the selection from among further estimates that are extremely discordant with
regard to the equivalent of that acid.20 The proportion of nitrate of potash, which I have obtained
by evaporating such a solution by a heat just sufficient to fuse the residuum, gave at the lowest in
three experiments 126, for the equivalent of nitrate of potash; from which, if we deduct 59.1
potash, there will remain 66.9 as the apparent equivalent of dry nitric acid. Consequently, I have
no hesitation in preferring the estimate21 to be obtained from Richter’s analysis of nitrate of
potash, which gives 67.45, from which, if we subtract one portion of azote 17.54, there remains
49.91, so nearly 5 portions of oxygen, that I consider the truth to be 17.54 + 50, or 67.54.
From this sketch of the mode in which such an inquiry may be pursued, wherever it is
necessary to make any original experiments, it will be fully understood what is meant by
15
Its separate existence is certainly imaginary, for it can no more be obtained uncombined than dry sulfuric acid, or
dry nitric acid. [Compare with “On the Acidifying Principle,” above.]
16
If all the steps in the series, by which the number 49.1 is inferred, be correct, this should be exactly 10.00 without
any fraction; and the proportion assigned to muriate of potash by Berzelius is sufficiently near, to show that there
can be no considerable error: 83.02 : 16.98 : : 49.1 : 10.04.
17
I avoid using the term carbonate of potash for either of these salts, because it has been applied to both, and
consequently is liable to be misunderstood when standing alone.
18
[A bi-carbonate is the same as a supercarbonate. It has twice as much carbonic acid in it—per weight of potash—
as has the subcarbonate. The bi-carbonate is made by bubbling large amounts of carbonic acid gas through a solution
of potash in water. The bi-carbonate of potash may then be crystallized out of this solution. On heating, it loses half
of its carbonic acid gas and becomes the subcarbonate of potash.]
19
Phil. Trans. 1808, p. 97.
20
[See the final paragraph of this essay, after the Data Table.]
21
46.7 : 53.3 : : 59.1 : 67.45, quoted in Mem. d’Arcueil, II. 59.
161
equivalents, and in what manner the series might be continued. I have, however, in most
instances drawn my inferences from former analyses, and indeed in all where I could find
coincidences between different authorities sufficient to give confidence in their results.
But with respect to oxalic acid, I again found a difficulty in deciding among the
discordant results of different analyses, and was obliged to have recourse to direct experiment.
100 grains of bin-oxalate of potash (commonly called salt of sorrel) were subjected to a degree of
heat sufficient to destroy the oxalic acid, and to convert the salt into a subcarbonate of potash.22
A quantity of muriatic acid was then poured on this residuum, and afterwards saturated with
carbonate of lime; and an equal quantity of the same acid was saturated with carbonate of lime
alone. By the excess of carbonate dissolved in the latter instance, it was found that 100 bin-
oxalate of potash was equivalent to 40.9 carbonate of lime; and hence the equivalent to 63
carbonate of lime will be 154 of the bin-oxalate of potash. After deducting 59.1 potash, the
remainder, 94.9 divided by 2, gives 47.45 for the equivalent of dry oxalic acid. I therefore again
adopt the result of the very industrious and ever accurate Berzelius, obtained by means of oxalate
of lead, that 296.6 litharge23 are combined with 100 oxalic acid, which are in the proportion of
139.5 litharge to 47.0 oxalic acid. Such a degree of accordance between methods totally different
appears highly satisfactory, and seems to show that in attempts to determine the same point by
means of lime, some compounds may possibly be formed at the same time differing in the
proportions of acid and base, as in the cases of oxalate and bin-oxalate of strontia observed by
Dr. Thomson, and that erroneous inferences may have been drawn from precipitates in which
they are blended.
With the exception of those instances that I have enumerated, there are few in which I
have found it necessary to make any new experiments, as I have met with coincidences between
the independent results of others sufficient to satisfy me in their correctness; and accordingly I
have adopted such determinations without any pretentions to improve upon them by new
experiments of my own.
It is not my design, in the table that follows this paper, to attempt a complete enumeration
of all those elements or compounds that I suppose to be well ascertained, but merely to include
some of those which most frequently occur. I do not offer it as an attempt to correct the estimates
that have been formed by others, but as a method in which their results may be advantageously
applied in forming an easy approximation to any object of our inquiries.
The means by which this is effected may be in part understood by inspection of the Plate
I. [p. 172], in which will be seen the list of substances intended to be estimated, arranged on one
or the other side of a scale of numbers in the order of their relative weights, that the series of
numbers placed on a sliding scale can at pleasure be moved, so that any number expressing the
weight of a compound may be brought to correspond with the place of that compound in the
adjacent column. The arrangement is then such that the weight of any ingredient in its
composition, of any reagent to be employed, or precipitate that might be obtained in its analysis,
will be found opposite to the point at which its respective name is placed.
In order to show more clearly the use of this scale, the Plate exhibits two different
22
[Oxalic acid contains carbon, and when salts of oxalic acid are decomposed by heat, carbonates are formed.]
23
Ann. De Chimie, No. 243. [Litharge is a lead oxide.]
162
situations of the slider, in one of which oxygen is 10, the other bodies being in their due
proportion to it, so that carbonic acid being 27.54, and lime 35.46, carbonate of lime is placed at
63.
In the second figure, the slider is represented drawn upwards till 100 corresponds to
muriate of soda; and accordingly the scale then shows how much of each substance contained in
the table is equivalent to 100 of common salt. It shows, with regard to the different views of the
analysis of this salt, that it contains 46.6 of dry muriatic acid, and 53.4 of soda, or 39.8 of
sodium, and 13.6 oxygen; or if viewed as chloride of sodium, that it contains 60.2 chlorine, and
39.8 sodium. With respect to reagents, it may be seen that 283 nitrate of lead, containing 191 of
litharge employed to separate the muriatic acid, would yield a precipitate of 237 muriate of lead,
and that there would then remain in solution nearly 146 nitrate of soda. It may at the same time
be seen that the [muriatic] acid in this quantity of [common] salt would serve to make 232
corrosive sublimate24 containing 185.5 red oxide of mercury, or would make 91.5 muriate of
ammonia, composed of 6 muriatic gas (or hydromuriatic acid) and 29.5 ammonia. The scale
shows also that, for the purpose of obtaining the whole of the [muriatic] acid in distillation, the
quantity of oil of vitriol25 required is nearly 84, and that the residuum of this distillation would be
122 dry sulfate of soda, from which might be obtained, by crystallization, 277 of Glauber salt
containing 155 water of crystallization. These and many more such answers appear at once by
bare inspection, as soon as the weight of any substance intended for examination is made by
motion of the slider correctly to correspond with its place in the adjacent column.
With respect to the method of laying down the divisions of this scale, those who are
accustomed to the use of other sliding-rules, and are practically acquainted with their properties,
will recognize upon the slider itself the common Gunter’s line of numbers (as it is termed), and
will be satisfied that the results that it gives are the same that would be obtained by arithmetical
computation.
Those who are acquainted with the doctrine of ratios, and with the use of logarithms as
measures of ratios, will understand the principle on which this scale is founded, and will not need
to be told that all the divisions are logometric, and consequently that the mechanical addition and
subtraction of ratios, here performed by juxtaposition, corresponds in effect to the multiplication
and division of the numbers by which those ratios are expressed in common arithmetical
notation.
To others who are not equally conversant with nature of logarithms, and consequently
have not so correct a conception of the magnitudes of ratios, some further explanation of the
mode in which the scale of equivalents is constructed will, I presume, be acceptable.
They will observe that the series of natural numbers are not placed at equal intervals on
the scale; but that at all equal intervals are found numbers that bear the same proportion to each
other. In fig. 3 [in Plate I.], some of the larger intervals alone are represented on a line similarly
divided. The succession of intervals, marked A, B, C, D, E, are all equal, and at these points of
division are placed numbers 1, 2, 4, 8, 16, which increase progressively by the same ratio. And
since the series 3 : 6 : 12 : 24 increase in the same ratio of 1 to 2, these intervals a, b, c, d, e, are
the same as the former. At another succession of different yet equal intervals, marked F, G, H, I,
24
[The mercuric chloride discussed by Proust and Berthollet. Cf. pp. 129-130.]
25
[Aqueous, or hydrated, sulfuric acid; see the Numerical Table of Equivalents, under Sulfuric Acid (dry).]
163
are placed numbers 1, 3, 9, 27, which increase regularly by an equal ratio of 1 to 3; and by means
of a pair of compasses it would be found that the interval from 2 to 6, or from 6 to 18 (which are
in the same ratio of 1 to 3), is exactly equal to FG, the interval between 1 and 3. As any single
space represents only one ratio, so the sum of any 2 or 3 equal spaces represents a double or
triple ratio. If 1 be increased 3 times by the ratio of 1 to 2, it becomes 8, which bears to 1 triple
the ratio of 2 to 1. This ratio is therefore rightly represented by AD, which is the triple of AB.
The distances of the intermediate numbers 5, 7, 10, 11, 13, etc. from 1, are likewise made
proportional to the ratios that they bear to 1, and are easily laid down by means of a table of
logarithms; for as these are arithmetic measures of the ratios that all numbers bear to unity, the
spaces proportional to them become linear representations of the same quantities.
As the entire spaces AD, AE represent the ratios of 8 and of 16 respectively to 1, so the
difference DE represents the ratio of 8 and 16, which stand at D and E, to each other. And in the
same manner, any other space kl represents correctly the ratio of 7 to 13; so that the measure of a
fraction expressed by quantities that are incommensurate is rendered as obvious to sight, as that
of any single multiple. And if a pair of compasses be opened to this interval, and transferred to
any other part of the scale, the points of the compasses will be found to rest upon numbers
bearing the same proportion to each other as those from which the interval was transferred.
It is exactly in this manner that the various points on the column of equivalents indicate
the several quantities sought in any given position of the slider. The relative distances at which
the articles are placed represent so many different openings of the compasses rendered
permanent and presented to view at once. In the table, which I shall place at the end of this
communication, the relation of the various substances enumerated to each other is expressed by
numbers. In the engraved scale of equivalents, the ratios of these numbers are represented by
logometric intervals at which they are placed, their several positions being determined by those
of their respective numbers on the slider, which is logometrically divided. Consequently all the
several points in the column of equivalents will indicate numbers in the same due proportions to
each other, whatever part of the scale may be presented to them. Those who seek information
may obtain it by inspection; those who already possess it may be able to correct the positions of
some articles by direct comparison with the best analyses upon record, in whatever numbers the
results of those analyses may happen to be expressed.
I hope that without trespassing too much on the time of the Society I shall have rendered
the principal and practical use of this scale intelligible. I trust that it will prove useful as an
assistant to chemists in general. It will at least serve for a specimen of the extreme facility of
mechanical approximation, which may very frequently be advantageously substituted for
computations that are often more laborious than the accuracy of our data warrants; and if it tends
to introduce into more general use that valuable instrument, the common sliding-rule, it will be
the means of saving no inconsiderable portion of time to those who are engaged in scientific
pursuits.
164
Numerical Table of Equivalents Hydrogen
(a)
1.32
Oxygen
10.00
Water
11.32
Carbon
(b)
7.54 + 20 Oxygen =
27.54 Carbonic acid
Sulfur
(f)
20.00 + 30 Oxygen =
50 Sulfuric acid
Phosphorus
(g)
17.40 + 20 Oxygen =
37.4 Phosphoric acid
Azote
(o)
17.54 + 50 Oxygen =
67.54 Nitric acid (q)
Muriatic acid (dry)
(e)
34.1 + 10 Oxygen =
44.1 Oxymuriatic acid
Chlorine
44.1= Oxymur.+1.32 Hydro.=
45.42 Muriatic gas
Oxalic acid
(b)
47.0
Ammonia
(p)
21.5
Soda
(l)
39.1 - 10 Oxygen =
29.1 Sodium
Potash
(m)
59.1 - 10 Oxygen =
49.1 Potassium
Magnesia
(n)
24.6
Lime
(c)
35.46 - 10 Oxygen =
25.46 Calcium
Strontia
(k)
69
Barytes
(i)
97
Iron
(r)
34.5 + 10 Oxygen =
+ 15 Oxygen =
44.5 Green Oxid. of Iron
49.5 Red Oxide Copper
(t)
40 + 10 Oxygen =
50 Black Oxid. Of Copp.
Zinc
(s)
41 + 10 Oxygen =
51 Oxid. of Zinc
Mercury
(v)
125.5 + 10 Oxygen =
135.5 Red Oxid. of Merc.
= 125.5 Merc.
= 261 Protoxid Merc. Lead
(d)
129.5 + 10 Oxygen =
139.5 Litharge
Silver
(u)
135 + 10 Oxygen =
145 Oxid.Silv. in Muriate
Subcarb. of
49.0 + 27.5 C. acid =
76.5 Bi-Carb.of
165
Ammonia Ammonia Subcarb. of Soda
66.6 + 27.5 C. acid + 11.3
Water =
105.5 BiCarb. Of Soda
Subcarb. of Potash
86 + 27.5 C.acid + 11.3 Water
=
125.5 BiCarb. of Potash
Carbonate of Lime
63
Carbonate of Barytes
124.5
Carbonate of Lead
167
Sulfuric acid (dry)
50 + 1 Water 11.3 =
61.3 Oil of Vitriol
(sp.gr. 1.85) Sulfate of Soda
89.1 + 10 Water 113.2 =
202.3 Glauber Salt
Sulfate of Potash
109.1
Sulfate of Magnesia
(n)
74.6 + 7 Water 79.3 =
153.9 Epsom Salt
Sulfate of Lime
85.5 + 2 Water 22.64 =
108.1 Selenite
Sulfate of Strontia
119.0
Sulfate of Barytes
147.0
Sulfate of Copper
156,6 =
1 Acid + 1 Oxid.
+ 5 Water 56.6 Sulfate of Iron
173. 8 =
1 Acid + 1 Oxid.
+ 7 Water 79.3 Sulfate of Zinc
180.2 =
1 Acid + 1 Oxid.
+ 7 Water 79.3 Sulfate of Lead
189.5
Nitric Acid (dry)
(q)
67.54 + 2 Water 22.64 =
90.2 Liquid Nitric Acid
(sp.gr. 1.50) Nitrate of Soda
106.6
Nitrate of Potash
126.6
Nitrate of Lime
103.0
Nitrate of Barytes
164.5
166
Nitrate of Lead 207.0 Muriate of Ammonia
66.9 =
1 Acid + 1 Ammonia
+ 1 Water Muriate of Soda
73.2
Muriate of Potash
93.2 + 60 Oxygen =
153.2 Hyper-Oxymuriate
of Potash Muriate of Lime
69.6
Muriate of Barytes
131.0 + 2 Water 22.6 =
153.6 Crystallized
Muriate of Barytes Muriate of Lead
173.6
Muriate of Silver
179.1
Corrosive Sublimate
170.6 =
1 Acid + 1 Oxygen
+ 1 Mercury Calomel
296.1 =
1 Acid + 1 Oxygen
+ 2 Mercury Phosphate of Lead
176.9
Oxalate of Lead
186.5
Bin-Oxalate of
Potash
153.0 =
2 Acid + 1 Potash
Data on which the Table is founded
(1) Composition of Water 88.286 : 11.714 : : Oxygen 10 : 1.327 Hydrogen (a)
+ 10.00 Oxygen
11.327 Water
(2) Specific Gravities 1.1036 : 1.5196 : : 2 Oxygen 20 : 27.54 Carbonic acid (b)
(3) Carbonate of Lime 43.7 : 56.3 : : Carb. acid 27.54 : 35.46 Lime (c)
(4) Carbonate of Lead 16.5 : 83.5 : : Carb. acid 27.54 : 139.5 Litharge
- 10 Oxygen
129.5 Lead (d)
(5) Litharge 7.15 : 92.85 : : Oxygen 10 : 129.7 Lead (d)
167
(6) Muriate of Lime from Carbonate of Lime
50.77 : 56.1 : : Carb. Lime 63 : 69.6 Mur. Lime
-35.5 Lime
34.1 Muriatic acid (e)
(7) Muriate of Lead 409.47 : 100 : : Litharge 139.5 : 34.1 Muriatic acid (e)
(8) Sulfate of Lead 279 : 100 : : Litharge 139.5 : 50.0 Sulfuric acid
-30 (= 3 Oxygen)
20 Sulfur (f)
(9) Galena 86.64 : 13.36 : : Lead 129.5 : 20 Sulfur (f)
(10) Galena 85.1 : 13 : : Lead 129.5 : 19.8 Sulfur (f)
(11) Phosphate of Lead 380.56 : 100 : : Litharge 139.5 : 37.4 Phosphoric acid
-20 (2 Oxygen)
17.4 Phosphorus (g)
(12) Phosphoric acid 53.28 : 46.72 : : Phosph. acid 37.4 : 20 Oxygen
-37.4 Phosph. acid
17.4 Phosphorus (g)
(13) Oxalate of Lead 296.6 : 100 : : Litharge 139.5 : 47.0 Oxalic acid (h)
(14) Carbonate of Barytes 100 : 352.57 : : Carb. acid 27.54 : 97 Barytes (i)
(15) Sulfate of Barytes 34 : 66 : : Sulph. acid 50 : 97 Barytes (j)
(16) Sulfate of Strontia 42 : 58 : : Sulph. acid 50 : 69 Strontia (k)
(17) Common Salt 134 : 88 : : Chlorine 44.1 : 29 Sodium (l)
-10 +10
Mur. acid 34.1 39.1 Soda
(18) Common Salt 100 : 114.78 : : Mur. acid 34.1 : 39.1 Soda
(19) Subcarbonate of Soda 41.24 : 58.76 : : Carb. acid 27.54 : 39.1 Soda
(20) Muriate of Potash 100 : 173.47 : : Mur. acid 34.1 : 59.1 Potash (m)
-10
49.1 Potassium
(21) Muriate of Potash Oxymur. acid or Chlorine +44.1
from Potassium 32 : 60.8 : : Potassium 49.0 : 93.2 Mur. Potash
168
(22) Sulfate of Magnesia 67 : 33 : : Sulph. acid 50 : 24.6 Magnesia (n)
+50
74.6 Sulph. Magnesia
(23) Epsom Salt 100 51.5 : 48.5 : : 7 Water 79.3 : 74.4 Sulph. Magnesia
(24) Specific Gravities .07321 : .96913 : : Hydrogen 1.327 : 17.54 Azote (o)
3 Hydrogen = 3 x 1.327 = + 3.98
21.52 Ammonia (p)
(25) Ammonia 1 Azote + 3 Hydrogen = 21.52 Ammonia
(26) Subcarb. Ammonia 56.02 : 43.98 : : Carb. acid 27.54 : 21.6 Ammonia (p)
(27) Bicarb. Ammonia 28.2 : 11.8 : : 2 Carb. acid 55.1 : 21. 6 Ammonia (p)
(28) Nitrate of Potash 46.7 : 53.3 : : Potash 59.08 : 67.45 Nitric acid (q)
(29) Nitric Acid 1 Azote + 5 Oxygen 50 + Azote 17.54 = 67.54 Nitric acid (q)
2 Water = 2 x 11.32 = +22.64
90.18 Liquid Nitric acid
(30) Marble dissolved 476 : 681 3/4 : : Carb. Lime 63 : 90.23 Liquid Nitric acid
(31) Oxide of Iron 22.5 : 25.7 : : Oxygen 10 : 34.5 Iron (r)
+10
44.5 Oxide of Iron
(32) Sulfate of Iron 28.9 : 25.7 : : Sulph. acid 50 : 44.5 Oxide of Iron
(33) Oxide of Zinc 24.41 : 100 : : Oxygen 10 : 41 Zinc (s)
40 Copper (t)
+10
(34) Black Oxide of Copper 20 : 100 : : Oxygen 10 : 50 Oxide of Copper
(35) Sulfate of Copper 32 : 32 : : Sulph. acid 50 : 50 Oxide of Copper
(36) Muriate Silver 19.05 : 80.95 : : Mur. acid 34.1 : 145 Oxide of Silver
- 10
135 Silver (u)
169
(37) Horn Silver 24.5 : 75.5 : : Chlorine 44.1 : 136 Silver (u)
(38) Sulpheret Silver 14.7 : 100 : : Sulfur 20 : 136 Silver (u)
(39) Red Oxide of Mercury 8 : 100 : : Oxygen 10 : 125 Mercury (v)
(40) Red Oxide of Mercury 30 : 380 : : Oxygen 10 : 126.6 Mercury (v)
(41) Corrosive Sublimate 2 x 67 : 380 : : Chlorine 44.1 : 125.4 Mercury (v)
+ 136.6 Red Oxide of Mercury
262 Protoxide
(42) Protoxide 1 Oxygen + 2 Mercury : 262 Protoxide of Merc.
(43) Protoxide 4 : 104 : : Oxygen 10 : 260 Protoxide of Merc.
(44) Calomel 11.5 : 88.5 : : Mur. acid 35.1 : 262 Protoxide of Merc.
Sources of Info :
(1) Biot and Arago
(2) Biot and Arago
(3) Experiment
(4) Berzelius
(5) Berzelius
(6) Marcet
(7) Berzelius
(8) Berzelius
(9) Berzelius
(10) Thomson
(11) Berzelius
(12) Rose
(13) Berzelius
(14) Berzelius
(15) Klaproth
(16) Berzelius
(17) Davy
(18) Berzelius
(19) Berzelius
(20) & (21) Berzelius
(22) Henry
(23) experiment
(24) Biot and Arago
(25) by hypothesis
(26) Gay Lussac
(27) Berthollet
(28) Richter
(29) by hypothesis
(30) R. Phillips
(31) Thenard
(32) Berzelius
(33) Gay Lussac
(34) Chenevix
(35) Proust
(36) Marcet
(37) Davy
(38) Wenzel
(39) Fourcroy &
Thenard
(40) Davy
(41) Davy
(42) by synthesis
(43) Fourcroy
(44) Chenevix
Water(w) contained in crystallized Salts
Sulfate of Copper... (45) 100 : 36.3 :: 156.6 : 56.8 = 5 x 11.36
Sulfate of Iron........ (46) 100 : 45.4 :: 173.8 : 79.0 = 7 x 11.28
Sulfate of Zinc........ (47) 100 : 44.3 :: 180.2 : 79.8 = 7 x 11.40
Sulfate of Magnesia (48) 100 : 51.5 :: 153.9 : 79.3 = 7 x 11.33
Glauber Salt............. (49) 100 : 56 :: 202.3 : 113.1 = 10 x 11.31
Muriate of Barytes... (50) 100 : 14.8 :: 153.6 : 22.8 = 2 x 11.48
(45) Berzelius (46) Berzelius (47) Lost by heat (48) by heat (49) Berzelius (50) Berzelius
In this table I have selected in most cases double evidence from different sources, in
order that the inferences might receive confirmation from their concurrence. Number (29) may
be noticed as a result anticipated from preceding data, and found to coincide with remarkable
170
accuracy.
In the distillation of nitric acid from nitre, the whole of the acid may be obtained, if we
employ enough of sulfuric acid to convert the residuum into bi-sulfate of potash. In this case
each portion of potash, from which dry nitric acid is separated, will displace the water from two
equivalent quantities of sulfuric acid, and each portion of nitric acid weighing 67.54 will be
found combined with 22.64 of water. Hence 90.18 of liquid nitric acid so obtained would
dissolve the equivalent 63 of carbonate of lime. And in fact, by an experiment carefully
conducted on a large scale by Mr. Phillips,1 it appears that 681¾ of such acid did dissolve 476 of
marble, which is in the proportion of 90.18 to 62.96, corresponding with the estimate within
1/1500 part, a degree of coincidence rarely to be found even in the repetition of the same
experiment by the most skillful analyst.
The specific gravity of this substance was found to be 1.50.
[On p. 172 is found a copy of Wollaston’s Logometric Slide Rule.]
Notes on the Reading
1. In reading the article by Wollaston, you should observe the following:
a. Study with care the examples on pp. 158-160. You may scan the remaining
examples in the reading.
b. Study with care the Numerical Table of Equivalents; you may scan the data on
which the table is founded.
2. What has been added to the “science of affinities” by Richter and Wollaston? What has
been added to the balanced equations of Lavoisier?
3. Can you give a succinct statement of the “Law of Equivalents”? This law might be called
the “Law of Ex Aequali Proportions.” Why?
4. The term “radical” refers to an element or (more commonly) a group of elements that act
as a unit in a series of chemical reactions; e.g., the sulfate “radical” that is composed of
sulfur and oxygen but that does not decompose in most chemical reactions.
5. The Law of Multiple Proportions is usually stated thus: “When one element (or radical)
combines with another element (or radical) in more than one proportion by weight, the
ratio of weights of the second element (or radical) that will combine with a given fixed
weight of the first element (or radical) will be as small whole numbers.”
6. Examine the logometric scale on p. 172 and figure out how to use it use it. If time
permits, answer the questions and problems on p. 171.
1 Experimental Examination of the Pharm. Lond, by R. Phillips.
171
Wollaston’s Equivalent Weight Slide Rule You will probably be supplied with a homemade Wollaston-slide rule. If so, notice that it
has been prepared by cutting strips out of Wollaston’s image on p. 172 and fixing them to an
ordinary slide rule. If you need to construct such a slide rule, photocopy the image on p. 172 and
tape it to a slide rule. Study this slide rule until you understand how to use it.
Questions and Problems
1. In Experiment 4, all the solutions of salts and barytes were of equal concentration in
terms of the number of equivalents of salt dissolved in the same volume of solution. Why
was this done? All the acids and bases (except the barytes) contained six equivalents of
acid or base per liter of solution. Do you see why one would expect that a given volume
of Caustic Soda solution would require the same volume of Muriatic Acid solution for
complete “saturation” of the base with acid? Do you also see why one would expect that
a given volume of Sulfate of Potash would require the same volume of barytes solution to
just complete the decomposition of the Sulfate of Potash?
2. How might one use Wollaston’s scale of equivalents if one were to accept the Law of
Multiple Proportions as valid? Does this law suggest that some elements (and radicals)
will have multiple equivalent weights?
3. If a 44 g sample of a Carbon oxide (Carbonic Acid gas) is found to contain, on analysis,
12 g of Carbon and 32 g of Oxygen, (a) what is the percentage composition of the
compound; i.e., the percentage of Carbon and the percentage of Oxygen? (b) How many
grams of Oxygen would combine with 10 g of Carbon?
4. Using the log. scale of equivalents, answer the following questions:
a. How many grams of water would be produced by burning Hydrogen in 10 g of
Oxygen?
b. How many grams of Chlorine would combine with 29 g of Sodium metal to form a
fixed composition compound?
c. How many grams of Calcium would react with the weight of Chlorine determined
in (b)?
d. How many grams of Copper would combine with 13.6 g of Oxygen?
172
Wollaston’s Logometric Equivalent-Weight Slide Rule
173
CHAPTER VI:
Chemical Combination and Electricity
Introduction
In Senior Natural Science you will consider the nature of electricity in some detail. However, in
order to understand significant developments in chemistry in the nineteenth century, we need to
have a brief, qualitative idea of what electricity is and how it is first known.
The gold-colored, fossilized tree sap commonly called “amber” the Greeks called
(electra), the feminine form of (electros), their word for a common alloy of
silver and gold. The Greeks knew that this stone, when rubbed, especially with animal fur, has
the unusual power of attracting light objects, and although they speculated about the cause of the
mysterious phenomenon, little careful study was made of amber for centuries. In the late
sixteenth century, however, William Gilbert1 showed that a number of other substances besides
amber gained an attractive power when rubbed, and dubbed such substances “electrics,” and said
they possessed “electricity.”
Before Lavoisier’s time, in the mid-18th century, it was recognized that there are two
“types” of electricity: one that could be put on amber (“resinous electricity”), and one that could
be put on glass, e.g., by rubbing it with silk (“vitreous electricity”). Such bodies were said to
possess a load, or in French a “charge,” of electricity. A body loaded with one kind of electric
charge would attract and be attracted to a body loaded with the other, whereas bodies with the
same kind of charge would repel each other. However, when attracting bodies were brought into
contact, they would lose their electricity altogether. This “neutralization” would occur even if the
two bodies were connected only by a metal substance,2 which latter came to be called a
“conductor” of electric charge.3
At about this same time Benjamin Franklin proposed that electricity in bodies should be
thought of as a single elastic electric fluid the parts of which are therefore mutually repulsive,
and that all bodies contain this fluid. Those with too much, Franklin said, have a “positive”
charge, and those with too little have a “negative” charge. Apparently thinking that the rubbing
of amber is in effect a rubbing off of some of its electric fluid, Franklin supposed that resinous
electricity is negative, and therefore vitreous electricity is positive. Franklin also surmised that
the spark sometimes seen between two oppositely charged bodies as they come close together is
in fact a pure form of this electric fluid; his famous kite-flying experiment likewise suggested
that lightning was electric in nature. (Franklin did not, however, have the final word on the
nature of electricity, as others proposed that there were two electric fluids, one corresponding to
each kind of electricity,4 and still others thought it was precipitous to speculate about electric
1 In Senior Natural Science you will read some of Gilbert’s De Magnete, on the equally peculiar lodestone.
2 Compare this use of the word “neutralize” with that in the acid-base reactions examined earlier.
3 Most metals are good conductors, whereas most compounds and non-metals are poor conductors.
4 Although Franklin’s theory readily explained why two positively charged bodies would repulse each other and two
oppositely charged ones would attract, it could not explain why two negatively charged bodies would repell one
174
fluids at all;5 what we have said, however, is sufficient for our purposes in the Sophomore
Natural Science.)
Not until a few years before Dalton was writing was there any way known for producing
electricity in a sustained way, i.e., such that the charge could be produced as quickly as it was
carried off by contact with a conductor. But in 1800 Alessandro Volta developed a new
apparatus:
The astonishing apparatus is nothing but an assemblage of a number of good
conductors of a different kind, arranged in a certain manner: Thus, 30, 40, 60
pieces or more, of copper, or better of silver, each applied to a piece of tin, or,
what is much better, of zinc, and an equal number of layers of water, or of some
other fluid which is a better conductor than simple water, such as salt water, lye,
etc., or pieces of cardboard, of leather, etc., well soaked in these fluids. … I place
then horizontally, on a table or any other stand, one of the metallic plates, for
example, one of silver, and to this first I add a second of zinc; on this second I add
a moistened disc; then another silver plate, followed immediately by another of
zinc, to which I add another moistened disc. I thus continue in the same fashion,
coupling a silver plate with one of zinc, and always in the same order, that is to
say, always the silver below and the zinc above, or vice versa, according to how I
began, and interposing between each of these couples a moistened disc; I
continue, I say, to form from the several stages a column as high as can be
sustained without falling.6
He called two plates of dissimilar metals separated by a moistened disc a “cell.” The
whole stack of cells, which he simply called a “battery” of cells, came to be called a “voltaic
pile.” After attaching conducting metal strips to either end of the battery, when Volta brought the
ends of the conductors together he produced a spark. Neither did the conductors become
neutralized once the spark was produced; somehow the metals in the saltwater medium were
producing an electric charge as fast as the conductors could carry it off. Volta had produced a
“current” of electric charge. This electric current came to be thought of as a “flow” of positive
charge or electricity through the conductor.
It was noticed that the zinc plates in the voltaic pile corroded rapidly; moreover, crystals
would sometimes form on the silver plates. It appeared that some sort of chemical reaction
involving the metals and the saltwater produced and maintained the electric current, so not only
another. Thus, Franklin’s contemporary, Henry Cavendish proposed that there are two electric fluid, and that like
fluids mutually repell, and unlike mutually attract.
5 Among others, Humphrey Davy’s assistant, Michael Faraday—whose extensive experimental and theoretical work
with electricity and magnetism you will study in Senior Natural Science—was cautious about the “electrical fluid,”
saying its existence is “entirely hypothetical, and [its] effects may perhaps depend on some property common to
matter in general. And this is more probable because there is no known matter but what under certain circumstances
can be made to exhibit these peculiar [electrical] phenomena” (Chemistry Lectures, p. 10).
6 Alexander Volta, “On the Electricity Excited by the Mere Contact of Conducting Substances of Different Kinds,”
Philosophical Transactions of the Royal Society of London 90 (1800): 403–31.
175
was the idea entertained that chemical reactions may have something to do with electricity,7 but
further it was asked whether perhaps electricity could be used to produce chemical reactions. The
former notion would not be developed in a consistent way until the beginning of the twentieth
century, but we will lay the groundwork for such a development in the paper by Berzelius (which
we will read shortly), and when we consider valence in Chapter VIII. The possibility of using the
voltaic pile to induce chemical reactions, however, was immediately put to use in the early
nineteenth century through a process called electrolysis ([lusis], “loosening,” or “setting
free”), which is the decomposition of a compound substance effected by an electric current. An
example of this process is shown in Demonstration 9.
7 With time permitting, your tutor may demonstrate the electrical character of acids by manifesting the electric
current that runs through an acid solution when two metals are immersed in it and connected by a conducting wire.
(A galvanometer can be used to indicate the presence of a current; prolongation of the demonstration should indicate
a decrease in acidity and current.) Do the results of this demonstration suggest that neither oxygen nor hydrogen, but
rather something called “electricity,” is the acidifying principle?
176
Davy’s Decomposition of the Alkalis and Salifiable Earths
Recall Lavoisier’s prediction that the alkalis and salifiable earths would probably prove
to be composite substances.8
At the end of a memoir of 1806, Davy made this suggestion: “If a chemical union be of
the nature that I have ventured to suppose, however strong the natural electrical energies of the
elements of bodies may be, yet there is every probability of a limit to their strength; whereas the
powers of our artificial instruments seem capable of indefinite increase.” We may therefore
“hope that the new mode of analysis may lead us to the discovery of the true elements of
bodies.”9
In 1807 Davy announced the decomposition of two alkalis by electricity:
Potash, perfectly dried by ignition, is a non-conductor, yet it is rendered a conductor, by a
very slight addition of moisture, which does not perceptibly destroy its aggregation; and in
this state it readily fuses10 and decomposes by strong electrical powers. A small piece of pure
potash, which had been exposed for a few seconds to the atmosphere so as to give
conducting power to the surface, was placed upon an insulated disc of platina,11 connected
with the negative side of a battery of 250 of the power of 6 and 4 (i.e., zinc and copper plates
6 in. and 4 in.) in a state of intense activity; and a platina wire, communicating with the
positive side, was brought in contact with the upper surface of the alkali. The whole
apparatus was in the open atmosphere. Under these circumstances a vivid action was soon
observed to take place. The potash began to fuse at both its points of electrization. There
was a violent effervescence at the upper surface (+); at the lower, or negative surface, there
was no liberation of elastic fluid; but small globules having a high metallic lustre, and being
precisely similar in visible characteristics to quicksilver, appeared, some of which burnt with
explosion and bright flame as soon as they were formed, and others remained, and were
merely tarnished, and finally covered with a white film that formed on their surfaces. These
globules numerous experiments soon showed to be the substance I was in search of, and a
peculiar inflammable principle the basis of potash.12
We are told by John Davy that when his brother “saw the minute globules of potassium
burst through the crust of potash, and take fire as they entered the atmosphere, he could not
contain his joy—he actually bounded about the room in ecstatic delight; and some little time was
required for him to compose himself sufficiently to continue the experiment.” An entry in
Davy’s notebook concludes with the statement: “Capital experiment, proving the decomposition
of potash.”
8 Elements of Chemistry, ch. XVI.
9 Quoted in Partington, A Short History of Chemistry, p. 183.
10
That is, it liquefies.
11
That is, platinum.
12
Partington, A Short History of Chemistry, pp. 183-184.
177
This discovery was made on the 6th of October, 1807; sodium was discovered in a
similar manner a few days later. In 1808 Davy also decomposed some of the salifiable earths. He
named the new elements he obtained magnesium, calcium, strontium, and barium. Now we can
confidently describe “soda” as sodium oxide, “potash” as potassium oxide, “barytes” as barium
oxide, “lime” as calcium oxide, “strontia” as strontium oxide, and “magnesia” as magnesium
oxide. Later even “argill” was shown to be aluminum oxide and “siles” silicon oxide.13
In view of the above, what becomes of the fourth and fifth classes of substances listed by
Morveau et al. (pp. 66-67)?
With the discovery of the compositeness of soda, etc., the names of some compounds
were changed (though the inertia of custom kept some chemists using the older names). For
example, carbonate of soda became carbonate of sodium, or, following the modern convention of
naming the more electropositive element first, sodium carbonate. The composition of the
compound remained the same, of course, but the analysis might be reported differently:
carbonate of soda contained 58.5% by weight of soda and 41.5% carbonic acid (anhydrous);
sodium carbonate contained 43.4% by weight of sodium and 41.5% carbonic acid (anhydrous)
and 15.1% oxygen not in carbonic acid.
13
Several of these oxides were later shown to contain a small amount of hydrogen, and so were called “hydroxides.”
Hydrogen’s miniscule weight made it difficult to detect.
178
Jöns Jacob Berzelius
The Electro-chemical Theory1
In many carefully made experiments, Volta has observed that two metals put in contact
become electric, and that this is the cause of the phenomena of the electric pile. Davy later
showed that this electrical state increases due to the force of mutual affinities of the bodies used,
and that this effect can be produced, and even seen, by means of certain precautions, in all bodies
that have affinity for each other. It also follows from the experiments of Davy that temperature,
which, as we know, increases affinity, also increases the intensity of the electrical state in bodies
that are in contact, but that, this mechanical contact being followed by combination, all signs of
electricity immediately cease; that is to say, at the instant when, in favorable circumstances, they
burst into flame, the electrical division, or the charge that could be perceived, disappears. These
facts agree well with the conjecture that the opposite electricities in the bodies that combine
mutually neutralize each other at the moment of combination, and then the fire is produced in the
same manner as in the electric discharge.
But if these bodies which are united and have ceased to be electric should again be
separated, and their elements be restored to the isolated state with their original properties, they
must recover the electrical state destroyed by the combination; or indeed, in other terms, if these
combined bodies are restored for any reason to their original electrical state, which had vanished
at their union, they must separate, and reappear with their original properties. Hisinger and I have
observed that when the electric pile exerts its action on a conducting liquid, the elements of this
liquid separate, oxygen and the acids are repelled from the negative pole toward the positive, and
the combustible bodies as well as the salifiable bases from the positive pole toward the negative.
We believe we now know with certitude that bodies that are likely to combine show free,
opposite electricities that increase in force as they approach the temperature at which
combination occurs, until, at the instant of union, the electricity disappears with an elevation of
temperature that is often so great that they burst into flame. On the other hand, we have the same
certainty that combined bodies, exposed in a suitable form to the action of the electric fluid
produced by discharge of a pile, are separated and regain their original chemical and electrical
properties at the same time that the electricity that acted on them disappears.
In the actual state of our knowledge, the most probable explanation of combustion and
the ignition that results from it is then: that in all chemical combinations there is neutralization
of opposing electricities, and that this neutralization produces fire in the same manner that it
produces it in the discharge of the electric jar, the electric pile, and thunder, without being
accompanied, in these latter phenomena, by chemical combination . . .
The experiments made on the mutual electrical relations of bodies have taught us that
they can be divided into two classes: electropositive and electronegative. The simple bodies that
belong to the first class, as well as their oxides, always take up positive electricity when they
1 [In 1819, Berzelius put forward his electrochemical or “dualistic” theory, which dominated the chemical world for
many years. His ideas were expressed in a small book, Essai sur la Théorie des Proportions chimiques et sur
l’influence chimique de l’électricite, Paris, 1819. The following selection, taken from pp. 70-76, expresses the
fundamental ideas of the theory.]
179
meet simple bodies or oxides belonging to the second class; and the oxides of the first class
always behave with the oxides of the other like salifiable bases with acids.
It has been believed that the electrical series of combustible bodies differs from that of
their oxides; but although the different degrees of oxidation of several bodies present exceptions,
the electrical order of combustible bodies agrees in general with that of their oxides, in such a
way that the strongest degrees of oxidation in the affinity of different radicals are like those
between the radicals themselves.
In arranging the bodies in the order of their electrical nature, there is formed an electro-
chemical system that, in my opinion, is more fit than any other to give an idea of chemistry. I
will speak more of this later.
Oxygen is, of all bodies, the most electronegative. As it is never positive relative to any
other, and as, according to all chemical phenomena known up to the present, it is not probable
that any element of our globe can be more electronegative, we recognize in it an absolute
negative. Also, in the electrochemical system, it is the only body whose electrical relations are
invariable. The others vary in this sense, that one body can be negative with respect to a second,
and positive with respect to a third: for example, sulfur and arsenic are positive relative to
oxygen and negative relative to metals. The radicals of fixed alkalis and alkaline earths are, on
the contrary, the most electropositive bodies; but they differ somewhat in degree; and, at the
positive extreme of the electrical series, there is no body as electropositive as oxygen is
electronegative.2
[The applications of this theory are illustrated by the following extract, taken from the French
edition of Berzelius’s textbook, Paris, 1831, volume 4.]
The electrochemical properties of oxidized substances depend almost always exclusively
on the unipolarity of their electropositive element, that is to say, of their radical. The oxide is
ordinarily electronegative with regard to other oxides when its radical is negative with regard to
their radicals, and vice versa. For example, sulfuric acid is electronegative in relation to all
metallic oxides, for the reason that sulfur is negative with respect to all metals. The oxides of
potassium and zinc are, on the contrary, electropositive with regard to all oxidized substances, to
the radicals of which potassium and zinc are positive. This fact, the cause of which we are unable
to explain, rectifies an inexact idea on the principle of acidity that in the antiphlogistic theory has
been thought to be oxygen. We find now that it resides in the radical of the acid and that oxygen
plays such an indifferent role that it enters equally into the strongest salifying bases, that is to
say, the electropositive oxides, and in the strongest acids or electronegative oxides. Sometimes it
happens, however, that a positive oxide acquires by higher oxidation less electropositive
properties approaching electronegative, as, for example, stannic oxide and the acids of
manganese. But in the strongest bases, such as potash and soda, an addition of oxygen may well
destroy the positive action without, nevertheless, producing a negative; it is thus that the strongly
salifying bases form peroxides . . .
If these electrochemical views are correct, it follows that all chemical combination
depends solely on two opposing forces, positive and negative electricity, and that thus each
2 [Since Berzelius’s time only the element fluorine, which had not yet been discovered, has been established as more
electronegative than oxygen.]
180
combination should be composed of two parts united by the effect of their electrochemical
reaction, provided that there exists no third force. Whence it follows that each compound
substance, regardless of the number of its constituent principles, may be divided into two parts,
of which one is electrically positive and the other negative. Thus, for example, sulfate of soda is
not composed of sulfur, oxygen, and sodium, but of sulfuric acid and soda, which both may
again be divided into two elements, one positive and the other negative. Similarly alum cannot
be considered as directly composed of its elements but should be regarded as the product of the
reaction of sulfate of aluminum, a negative element, and sulfate of potash, a positive element. In
this manner the electrochemical view equally well justifies what I have already detailed on
particular compounds of the first, second, and third orders, etc.
* * * * *
Questions and Problems
1. Using Berzelius’s theory, explain the combination of potassium with oxygen to form potassium
oxide, the combination of sulfur with oxygen to form sulfuric acid (anhydrous), and the
combination of these products to form sulfate of potash (potassium sulfate).
2. Free elements merely mechanically mixed do not migrate to any noticeable extent when placed
between charged poles. Thus they seem to behave as though they were electrically neutral. Also,
some compounds (known to be compounds by their method of formation and by indirect method
of decomposition) do not electrolyze under the conditions familiar to Davy and Berzelius; the
carbon oxides are examples. Can these phenomena be accommodated by Berzelius’s theory? If
electricity explains why atoms come together, can they explain their cohesion in a molecule, since
at this point the electricity “disappears,” as Berzelius put it on p. 178?
3. Does Berzelius’s theory add to the science of affinities? Does it make a significant contribution to
the explanation of the nature of chemical substances and chemical combinations? You may find it
fruitful to compare it to the teaching of Aristotle and St. Thomas on how elements are preserved
in combination.
4. Consider the following words of Jean Baptiste Dumas about Berzelius’s electro-chemical theory
after it had gained wide acceptance in the mid-19th century:
These electrochemical conceptions, this special polarity which has been assigned to the
elementary atoms, do they really rest on such evident facts that they may be accepted as articles
of faith? Or, if we regard them only as hypotheses, do they possess the property of adapting
themselves to the facts, are they capable of explaining them, can we assume them with such
complete certainty that in chemical investigations they appear as useful guides? We must admit
that such is not the case.3
How certain does it seem that electricity is the cause of chemical combination, based on what we
have seen? In the further development of the atomic theory (in the remaining chapters of this
manual), we will see some of the consequences of the Berzelius’s theory.
3 Quoted in Partington, Short History of Chemistry, p. 243.
181
CHAPTER VII:
Determination of Atomic and Molecular Weights
Lorenzo Amadeo Avogadro
Essay on a Manner of Determining the Relative Masses of the Elementary Molecules
of Bodies, and the Proportions in Which They Enter into these Compounds1
I
Mr. Gay-Lussac has shown in an interesting memoir that gases always unite in a very simple
proportion by volume, and that when the result of the union is a gas, its volume is also very
simply related to those of its components. But the quantitative proportions of substances in
compounds seem only to depend on the relative number of molecules2 that combine, and on the
number of composite molecules that result. It must then be admitted that very simple relations
also exist between the volumes of gaseous substances and the numbers of simple or compound
molecules that form them. The first hypothesis to present itself in this connection, and apparently
even the only admissible one, is the supposition that the number of integral molecules in any
gases is always the same for equal volumes, or always proportional to the volumes. Indeed, if we
were to suppose that the number of molecules contained in a given volume were different for
different gases, it would scarcely be possible to conceive that the law regulating the distance of
molecules could give in all cases relations between the volume and the number of molecules so
simple as those that the facts just detailed compel us to acknowledge. On the other hand, it is
very well conceivable that the molecules of gases being at such a distance that their mutual
attraction cannot be exercised, their varying attraction for caloric may be limited to condensing a
greater or smaller quantity around them, without the atmosphere formed by this fluid having any
greater extent in the one case than in the other, and, consequently, without the distance between
molecules varying; or, in other words, without the number of molecules contained in a given
volume being different. Dalton, it is true, has proposed a hypothesis directly opposed to this,
namely, that the quantity of caloric is always the same for the molecules of all bodies whatsoever
in the gaseous state, and that the greater or less attraction for caloric only results in producing a
1 [Journal de Physique, LXXIII (1811), pp. 58-76.]
2 [Avogadro has been accused of inconsistency in his use of the term “molecule,” but a careful perusal of his paper
will show that he uses it with its qualifying adjectives quite consistently, as follows:
Molecule (translated molecule): without qualification means in modern chemical phraseology either atom or
molecule.
Molecule integrante (translated integral molecule): means molecule in general, but is usually only applied to
compounds.
Molecule constituante (translated constituent molecule): is employed to denote the molecule of an elementary
substance.
Molecule elementaire (translated elementary molecule) stands for the atom of an elementary substance.]
182
greater or less condensation of this quantity around the molecules, and thus varying the distance
between the molecules themselves. But in our present ignorance of the manner in which this
attraction of the molecules for caloric is exerted, there is nothing to decide us a priori in favor of
the one of these hypotheses rather than the other; and we should rather be inclined to adopt a
neutral hypothesis, which would make the distance between the molecules and the quantities of
caloric vary according to unknown laws, were it not that the hypothesis we have just proposed is
based on that simplicity of relation between the volumes of gases on combination, which would
appear to be otherwise inexplicable.
Setting out from this hypothesis, it is apparent that we have the means of determining very
easily the relative masses of the molecules of substances obtainable in the gaseous state, and the
relative number of these molecules in compounds; for the ratios of the masses of the molecules
are then the same as those of the densities of the different gases at equal temperature and
pressure, and the relative number of molecules in a compound is given at once by the ratio of the
volumes of the gases that form it. For example, since the numbers 1.10359 and 0.07321 express
the densities of the two gases oxygen and hydrogen compared to that of atmospheric air as unity,
and the ratio of the two numbers consequently represents the ratio between the masses of equal
volumes of these two gases, it will also represent on our hypothesis the ratio of the masses of
their molecules. Thus the mass of the molecule of oxygen will be about 15 times that of the
molecule of hydrogen, or, more exactly, as 15.074 to 1. In the same way the mass of the
molecule of nitrogen will be to that of hydrogen as 0.96913 to 0.07321, that is, as 13, or more
exactly 13.238, to 1. On the other hand, since we know that the ratio of the volumes of hydrogen
and oxygen in the formation of water is 2 to 1, it follows that water results from the union of each
particle of oxygen with two particles of hydrogen. Similarly, according to the proportions
established by Mr. Gay-Lussac for the elements of ammonia, nitrous oxide, nitrous gas, and
nitric acid, ammonia will result from the union of one molecule of nitrogen with three of
hydrogen, nitrous oxide from one molecule of oxygen with two of nitrogen, nitrous gas from one
molecule of nitrogen with one of oxygen, and nitric acid from one of nitrogen with two of
oxygen.
II
There is a consideration that appears at first sight to be opposed to the admission of our
hypothesis with respect to compound substances. It seems that a molecule composed of two or
more elementary molecules should have its mass equal to the sum of the masses of these
molecules; and that in particular, if in a compound one molecule of one substance unites with
two or more molecules of another substance, the number of compound molecules should remain
the same as the number of molecules of the first substance. Accordingly, on our hypothesis when
a gas combines with two or more times its volume of another gas, the resulting compound, if
gaseous, must have a volume equal to that of the first of these gases. Now, in general, this is not
actually the case. For instance, the volume of water in the gaseous state is, as Mr. Gay-Lussac has
shown, twice as great as the volume of oxygen that enters into it, or, what comes to the same
thing, equal to that of the hydrogen instead of being equal to that of the oxygen. But a means of
explaining facts of this type in conformity with our hypothesis presents itself easily enough; we
suppose, namely, that the constituent molecules of any simple gas whatever (i.e., the molecules
that are at such a distance from each other that they cannot exercise their mutual action) are not
183
formed of a solitary elementary molecule, but are made up of a certain number of these
molecules united by attraction to form a single one; and further, that when molecules of another
substance unite with the former to form a compound molecule, the whole molecule that should
result splits up into two or more parts (or integral molecules) composed of half, quarter, etc., the
number of elementary molecules going to form the constituent molecule of the first substance
(or, what comes to the same thing, combined with a number equal to this last of half-molecules,
quarter-molecules, etc., of the second substance); so that the number of integral particles of the
compound becomes double, quadruple, etc., what it would have been if there had been no
splitting-up, and exactly what is necessary to satisfy the volume of the resulting gas.3
On reviewing the various compound gases most generally known, I only find examples of
duplication of the volume relatively to the volume of that one of the constituents that combines
with one or more volumes of the other. We have already seen this for water. In the same way, we
know that the volume of ammonia gas is twice that of the nitrogen that enters into it. Mr.
Gay-Lussac has also shown that the volume of nitrous oxide is equal to that of the nitrogen that
forms part of it, and consequently is twice that of the oxygen. Finally, nitrous gas, which contains
equal volumes of nitrogen and oxygen, has a volume equal to the sum of the two constituent
gases, that is to say, double that of each of them. Thus in all cases there must be a division of the
molecule into two; but it is possible that in other cases the division might be into four, eight, etc.
The possibility of this division of compound molecules might have been conjectured a priori; for
otherwise the integral molecules of bodies composed of several substances with a relatively large
number of molecules, would come to have a mass excessive in comparison with the molecules of
simple substances. We might therefore imagine that nature had some means of bringing them
back to the order of the latter, and the facts have pointed out to us the existence of such means.
Besides, there is another consideration that would seem to make us admit in some cases the
division in question: For how could one otherwise conceive a real combination between two
gaseous substances uniting in equal volumes without condensation, such as takes place in the
formation of nitrous gas? Supposing the molecules to remain at such a distance that the mutual
attraction of those of each new gas could not be exercised, we cannot imagine that a new
attraction could take place between the molecules of one gas and those of the other. But on the
hypothesis of division of the molecule, it is easy to see that the combination really reduces two
different molecules to one, and that there would be contraction by the whole volume of one of the
gases if each compound molecule did not split up into two molecules of the same nature. Mr.
Gay-Lussac clearly saw that, according to the facts, the diminution of volume on combination of
gases cannot represent the approximation of their elementary molecules. The division of
molecules on combination explains to us how these two things may be made independent of each
other.
III
Dalton, on arbitrary suppositions as to the most likely relative number of molecules in
compounds, has endeavored to fix ratios between the masses of the molecules of simple
3 Thus, for example, the integral molecule of water will be composed of a half-molecule of oxygen with one
molecule, or, what it the same thing, two half-molecules of hydrogen.
184
substances. Our hypothesis, supposing it well-founded, puts us in a position to confirm or rectify
his results from precise data, and, above all, to assign the magnitude4 of compound molecules
according to the volumes of the gaseous compounds, which depend partly on the division of
molecules entirely unsuspected by this physicist.
Thus Dalton supposes5 that water is formed by the union of hydrogen and oxygen, molecule
to molecule. From this, and from the ratio by weight of the two components, it would follow that
the mass of the molecule of oxygen would be to that of hydrogen as 7½ to 1 nearly, or, according
to Dalton’s evaluation, as 6 to 1. This ratio on our hypothesis is, as we saw, twice as great,
namely as 15 to 1. As for the particle of water, its mass ought to be roughly expressed by 15 + 2
= 17 (taking for unity that of hydrogen), if there were no division of the molecule into two; but on
account of this division it is reduced to half, 8½, or more exactly 8.537, as may also be found
directly by dividing the density of aqueous vapor 0.625 (Gay-Lussac)6 by the density of
hydrogen 0.0732. This mass only differs from 7, that assigned to it by Dalton, by the difference
in values for the composition of water; so that in this respect Dalton’s result is approximately
correct from the combination of two compensating errors—the error in the mass of the molecule
of oxygen, and his neglect of the division of the molecule.
Dalton supposes that in nitrous gas the combination of nitrogen and oxygen is molecule to
molecule, we have seen on our hypothesis that this is actually the case. Thus Dalton would have
found the same molecular mass for nitrogen as we have, always supposing that of hydrogen to be
unity, if he had not set out from a different value for that of oxygen, and if he had taken precisely
the same value for the quantities of the elements in nitrous gas by weight. But by supposing the
molecule of oxygen to be less than half what we find, he has been obliged to make that of
nitrogen also equal to less than half the value we have assigned to it, viz., 5 instead of 13. As
regards the molecule of nitrous gas itself, his neglect of the division of the molecule makes his
result approach ours; he has made 6 + 5 = 11, whilst according to us it is about 15 + 13 = 2
28
=14, or more exactly,
2
238.13074.15 = 14.156, as we also find by dividing 1.03636, the density of nitrous gas
according to Gay-Lussac, by 0.07321. Dalton has likewise fixed in the same manner as the facts
have given us, the relative number of molecules in nitrous oxide and in nitric acid, and in the first
case the same circumstance has rectified his result for the magnitude of the molecule. He makes
it 6 + (2 x 5) = 16, whilst according to our method it should be 2
)238.132(074.15 = 20.775, a
number that is also obtained by dividing 1.52092, Gay-Lussac’s value for the density of nitrous
oxide, by the density of hydrogen.
In the case of ammonia, Dalton’s supposition as to the relative number of molecules in its
4 [That is, the relative weight of the compound molecule.]
5 In what follows I shall make use of the exposition of Dalton’s ideas given in Thomson’s System of Chemistry.
6 [On p. 148 Gay-Lussac gave the ratio of the weights to be 10 to 16, which is the same as 0.625 : 1. All of the
values for the densities cited for the rest of this section can be found on p. 148.]
185
composition is on our hypothesis entirely at fault. He supposes nitrogen and hydrogen to be
united in it molecule to molecule, whereas we have seen that one molecule of nitrogen unites
with three molecules of hydrogen. According to him the particle of ammonia would be 5 + 1 = 6;
according to us it should be (13 + 3) divided by 2 = 8, or more exactly 8.119, as may also be
deduced directly from the density of ammonia gas. The division of the molecule, which does not
enter into Dalton’s calculations, partly corrects in this case also the error that would result from
his other suppositions….
VI
Let us now apply our hypothesis to some metallic substances. Mr. Gay-Lussac7 assumes that
mercurous oxide, in the formation of which 100 parts by weight of mercury absorb 4.16 of
oxygen, according to Fourcroy and Thenard, is analogous to nitrous oxide, i.e., that the mercury,
supposed gaseous, is combined in it with half its volume of oxygen gas, which on our hypothesis
is to say that one molecule of oxygen combines with two molecules of mercury. Supposing this
to be the case, the density of mercury gas ought to be to that of oxygen as 100 to 8.32, which
would give 13.25 as its density, taking that of air as unity, and for the mass of the molecule of
mercury 181, taking as unity that of hydrogen. On this supposition mercuric oxide, which
contains twice as much oxygen, should be formed of mercury and oxygen united molecule to
molecule; but some reasons lead me to think that it is mercurous oxide that represents this last
case, and that in mercuric oxide one molecule of mercury combines with two of oxygen. Then
the density of mercury gas, and the mass of its molecule, would be double what they are on the
preceding hypothesis, viz., 26½ for the first, and 362 for the second. In this assumption I am
supported from analogies drawn from other metals, and particularly from iron. It follows from
the experiments of different chemists, carefully discussed by Hassenfratz, that the two best
known oxides of iron, the black oxide and the red oxide, are composed respectively of 31.8 and
45 parts by weight of oxygen to 100 of iron. We see that the second of these two quantities of
oxygen is nearly half as great again as the first, so we are naturally led to suppose that in the first
oxide one molecule of iron combines with two molecules of oxygen, and in the second with
three. If that is so, and if we admit that the proportion for the black oxide to be the more exact,
the proportion for the red oxide would be 47.7 for 100 of iron, which comes very near to the
proportion found directly by Proust, viz., 48. The mass of a molecule of iron will therefore be to
the mass of a molecule of oxygen as 100 to 15.9, which gives about 94 with regard to hydrogen
as unity. It would appear from this that there should be another oxide of iron that would contain
15.9 of oxygen to 100 of iron, and this is perhaps the white oxide, although the experiments
hitherto performed point to this substance containing a greater proportion of oxygen. Now the
two oxides of mercury of which we have spoken, one of which contains twice as much oxygen as
the other, should apparently be analogous to this last oxide of iron and to the black oxide, the red
oxide having no analogue in the case of mercury. In the same way the other molecules present
for the most part two oxides in which the quantities of oxygen are as 1 to 2, so that from the
proportion of their elements by weight, we may determine in the same manner the mass of their
molecules. I find, for example, 206 for the molecule of lead, 198 for that of silver, 123 for
7 [See p. 150.]
186
copper, etc.8
VII
We shall now make a few applications of our principles to saline compounds, which will
furnish us with the opportunity of examining an important point in the theory of these
compounds. Mr. Gay-Lussac has shown that the neutral carbonate, fluoborate, and muriate of
ammonia are composed of equal volumes of ammonia gas and of the respective acids. Let us
pause to consider the carbonate. On our hypothesis, this salt is composed of one molecule of
ammonia, i.e. (according to the values previously given and independently of any division), of
one molecule of carbon, two of oxygen, and three of hydrogen, which would give 57.75 for the
mass of its molecule; but admitting the division into two which had already taken place in the
components, this molecule is reduced to 28.87. It would be brought down again to half this
number, if there were another division on the union of the acid with the alkali.
Mr. Gay-Lussac has suspected9 that the equality of volume between a gaseous alkali and
acid, which by their union form a neutral salt, may be general. That is as much as to say, on our
hypothesis, that neutral salts are composed of acid and alkali united molecule to molecule; but
certain considerations appear to be opposed to the admission of this principle in all its generality.
The idea of acidity, alkalinity, and neutrality which still seems to me the most conformable to the
phenomena is that which I have given in my Memoir on this subject (Journal de Physique, tome
lxix.). According to it, all substances form amongst themselves a series, in which they play the
part of acid or alkali with respect to one another; and this series is the same as that on which
depends the positive or negative electricity they develop on mutual contact. I express by the term
oxygenicity the property in virtue of which substances are ranked in this scale, placing first those
which play the part of an acid with respect to the others. In this scale there is a point about which
are placed the substances we term neutral, above it are those which are absolutely acid, below it
are those which are alkaline, when their state of aggregation permits them to exhibit these
qualities. Lastly, composite substances occupy in this scale a place intermediate between those of
which they are composed, having regard to the degree of the oxygenicity and to the proportion
8 I shall here add a few words regarding the molecule of potassium. Davy, assuming that potash is formed from
potassium and oxygen united molecule to molecule, has fixed the mass of the molecule of potassium at 40.5, in
accordance with the quantity of oxygen by weight in the substance, and has taken the molecule of oxygen to be 7.5.
Assuming, as we have done, this last molecule to be nearly twice as great, the molecule of potassium will also be
doubled, viz., about 81, if we adopt the other assumptions of Davy. But it may be that in potash one molecule of
potassium takes two of oxygen, in which case we should again have to double the last value and make it 162. It
might also be (for the analogy drawn from other metals is not in this case a very safe guide) that two molecules of
potassium combine with one of oxygen, which would bring back the molecule of potassium to 40.5.
It is on the assumption of this last value for the molecule of potassium that Davy finds 32.9 for that of
oxymuriatic acid, calculating from the composition of muriate of potash, and assuming that this salt is formed of one
molecule of potassium with one of acid. If we suppose the molecule of potassium to have a different mass, we must
admit another relative number of molecules in the muriate, since both from our hypothesis and from the density of
the gas, 32.9 is very nearly the molecule of oxymuriatic acid. On the supposition that the molecule of potassium is
81, and that in sulfide of potassium the combination is molecule to molecule, the molecule of sulfur will be about 27
instead of 13.5, as found by Davy on the latter assumption, which will bring about between this result and that
derived from sulfurous acid according to our calculations the agreement that exists between Davy’s values.
9 [Gay-Lussac proposed this notion on p. 144.]
187
by weight of these constituent substances; so that a neutral substance results from the
combination of two substances, one acid, the other alkaline, in a certain proportion.10 The
recognition of the simple ratios observed on combination, and in particular in cases where
neutral substances are the result, leads us now to a more exact manner of conceiving the state of
neutrality. The oxygenicity in two bodies that combine cannot be supposed to have such a
relation to the masses of their molecules that, from the union of certain definite numbers of these
molecules, there should result a certain definite degree of oxygenicity that would be that of
neutrality, and would only depend, as we have already assumed for oxygenicity in general, on
the proportion by weight and the degree of oxygenicity of the components. It appears, then, that
the we must admit that the degree of oxygenicity that corresponds to neutrality is not quite fixed,
although approximating more or less to a fixed limit, and that this state depends on the excess of
mass of one of the components (from which the acid or alkaline quality might result) being
prevented from exercising these qualities by the simple combination with the contrary principle
that retains it by its attraction, although the compound otherwise might have a state of
aggregation permitting it to act as an acid or an alkali, if it were endowed with these qualities.
The excess of mass thus held back is that which is necessary to complete a certain simple
relation between the number of combining molecules. Thus amongst the different simple ratios
in which molecules can combine, there is one which gives neutrality; that, namely, which gives
the compound approximating most closely to the definite point of oxygenicity mentioned above,
so that if, in the compound formed according to this ratio, one of the component principles let
one molecule of the other escape, or took up one in addition, then the compound would diverge
further from this precise point, about which there oscillate, as it were, the oxygenicities of the
various neutral compounds. And it is this point that would give the neutral state in the
combination of two substances that could combine in all proportions, or in ratios expressible by
any number of molecules whatever. It is evident that this way of regarding the neutrality of
compound substances reconciles the theory given in the Memoir quoted with the ideas put
forward by Mr. De Laplace on this point, and expounded by Mr. Hauy in his Traité de Physique.
According to this theory it is evident that if the oxygenicity of two acids and two alkalies
that combine respectively in pairs is not extremely different, and if at the same time the mass of
the molecule of one of the acids is not in a different ratio to its alkali from that of the other acid
with regard to its own alkali, then the ratio between the numbers of molecules that gives
neutrality may be the same in both compounds; but in the contrary case, the ratio may vary in
such a way that instead of the equality of volumes, or of combination of molecule to molecule
that we see between carbonic and a few other acids on the one hand and ammonia on the other,
there may be other simple ratios such as 1 to 2, etc., which give the neutral state. Nevertheless,
the simplicity that will always exist amongst these ratios, in conjunction with the information we
may obtain from other sources as to the mass of the molecules and the degree of oxygenicity of
the components, will sometimes put us in a position to determine, or at least conjecture, what are
the simple ratios that may occur in a given case; but it is the task of experiment to confirm these
theoretical estimates.
10
The properties of oxymuriatic acid, as Davy conceives them, being analogous to those of oxygen, are not at all
extraordinary from this point of view; they simply show that this substance is very oxygenic. I had already remarked
in my Memoir that the properties of the alkalies, supposed to be oxides, are easily explained according to these
ideas.
188
VIII
It will have been in general remarked on reading this Memoir that there are many points
of agreement between our special results and those of Dalton, although we set out from a general
principle, and Dalton has only been guided by considerations of detail. This agreement is an
argument in favor of our hypothesis, which is at bottom merely Dalton’s system furnished with a
new means of precision from the connection we have found between it and the general fact
established by Mr. Gay-Lussac. Dalton’s system supposes that compounds are made in general in
fixed proportions, and this is what experiment shows with regard to the more stable compounds
and those more interesting to the chemist. It would appear that it is only combinations of this sort
that can take place amongst gases, on account of the enormous size of the molecules that would
result from ratios expressed by larger numbers, in spite of the division of the molecules, which is
in all probability confined within narrow limits. We perceive that the close packing of the
molecules in solids and liquids, which only leaves between the integral molecules distances of
the same order as those between the elementary molecules, can give rise to more complicated
ratios, and even to combinations in all proportions; but these compounds so too will be of a
different type from those with which we have been concerned, and this distinction may serve to
reconcile Mr. Berthollet’s ideas as to compounds with the theory of fixed proportions.11
* * * * *
Questions on the Reading: 1. Are Avogadro’s hypotheses consistent with Berzelius’s theory of electro-chemistry and Dalton’s
supposition that particles of the same kind repel each other and (cf. p. 138)? That is, what is the
plausibility of a molecule composed of an oxygen atom combined with another oxygen atom?
2. When Avogadro specifies that the number of molecules in a given volume is the same for all
gases he does not claim to know that number—how could he?—nor does his law require that the
number be known, but only that it exist. The number was, however, finally determined at the
beginning of the 20th century by Jean Perrin, who named the number after him: “Avogadro’s
number” is 6.029 x 1023
molecules in 22.4 liters of any gas.
11
[Although he wrote it in French, one of the two common languages being used in most chemistry publications at
this time, for almost half a century Avogadro’s paper remained largely unknown or ignored outside of Italy. As a
result, chemists continued to struggle with the apparent conflict between Gay-Lussac’s law and Dalton’s atomic
theory during this period. However, in 1860 at an international conference in Karlsruhe, Germany, Stanislao
Cannizzaro would deliver a speech that would free Avogadro’s theory from obscurity; we will read Cannizzaro’s
paper shortly. In 1856 Avogadro himself passed away, his ideas still generally unrecognized.]
189
Modern Chemical Symbols12
In 1814, Berzelius published an article entitled On the Chemical Signs, and the Method of
Employing Them to Express Chemical Proportions. In criticizing the pre-Daltonian alchemical
symbols, he wrote, “They owed their origin, no doubt, to the mysterious relation supposed by the
alchemists to exist between the metals and the planets, and to the desire that they had of
expressing themselves in a manner incomprehensible to the public.” Berzelius commended the
work of “fellow-laborers in the anti-phlogistic revolution” (e.g., Dalton) in designing new signs.
He continued, “but, though we must acknowledge that these signs were very well contrived, and
very ingenious, they were of no use; because it is easier to write an abbreviated word than to
draw a figure, which has but little analogy with letters, and which, to be legible, must be made of
a larger size than our ordinary writing.” Berzelius then proposed his system: “The chemical signs
ought to be letters, for the greater facility of writing, and not to disfigure a printed book . . . I
shall take, therefore, for the chemical sign, the initial letter of the Latin name for each
elementary substance . . .” Further, since the names of some elements have the same initial
letters, the single letters were given to non-metals; e.g., for carbon, hydrogen, oxygen, sulfur, and
nitrogen we have C, H, O, S, and N. For metals that have an initial letter the same as a non-
metal, the first two distinctive letters were used; e.g., for copper, sodium, tin, and antimony
(whose Latin names are cuprium aes, natrium, stannum, and stibium) we have Cu, Na, Sn, and
Sb. Some slight modifications in this procedure were made by Berzelius and others. This system
is the one we use to this day. You will find a list of chemical symbols in the Appendix to Chapter
IX, at the back of the manual.
Berzelius’s interest went beyond convenient labeling. His symbols were “destined solely
to facilitate the expression of chemical proportions.” Thus the symbols are to be used in writing
out chemical formulas that specify the ratios of atoms in the compounds. For example, H2O
means that water is composed of molecules of two atoms of hydrogen and one of oxygen. The
subscript refers to the number of atoms of the element whose letter symbol immediately precedes
the subscript. If brackets are present, as in calcium hydroxide, Ca(OH)2, then the subscript
indicates that all the atoms inside the brackets, here being OH, are taken twice.13 Thus, H2SO4
means that sulfuric acid is composed of molecules of two atoms of hydrogen, one of sulfur, and
four of oxygen. If atomic weights are established for the elements, then the ratio of atoms also
implies a weight ratio. For example, if the atomic weight of H is 1, and of O is 16, then the
formula H2O tells us that water contains two parts by weight of hydrogen for sixteen parts by
weight of oxygen.
We can now replace word equations with symbol equations. Thus “carbon plus oxygen
yields carbon dioxide” becomes: C + O2 = CO2.
If the relative atomic weight of H is taken as 1 (that is, it is the standard for reference)
and the relative atomic weight of oxygen is considered as 8 (which is near the weight Dalton
gives it), is it possible to establish a formula for water? If so, how does it compare with H2O? If
12
This may be taken up any time before Canizzaro’s paper, but it may be best saved until after reading Avogadro—
where the distinction between molecules and atoms is introduced, and the constitution of water settled.
13
Berzelius actually used superscripts. (Superscripts now are reserved for describing ion-charge.) In the rest of this
manual, although Cannizzaro and others used superscripts, we have followed the modern notation.
190
it is different, how can one decide which (if indeed either) is correct?
A balanced equation is one in which the atomic constitution of all the substances reacted
are known and indicated on the left-hand side, and the atomic constitution of all the substances
produced are known and are indicated on the right-hand side, and the number of atoms of each
element is the same on either side of the equation.
In balancing a given equation keep in mind two rules:
1. The Law of Conservation of Matter must be adhered to (and no transmutation of elements
is allowed). The number of atoms of an element must be the same on each side of the
equation.
2. A coefficient (which refers to the number of molecules taken) may be changed in
balancing an equation, but a subscript (which specifies the atomic composition of the
given molecule of the given substance, and is based on the Law of Fixed Proportions)
may not be changed.
Example: Given that hydrogen gas and oxygen gas are observed to saturate one another and
produce water, balance the equation describing the reaction.
H2 + O2 = H2O This format violates Rule 1: it is not balanced.
H2 + O2 = H2O2 This format conforms to Rule 1, but it violates Rule 2, so it is
also incorrect.
2H2 + O2 = 2H2O This format follows both rules, and is therefore correct.
* By convention, if a reactant (a substance on the left-hand side of an equation) or product (a
substance on the right-hand side) is a gas at room temperature, an arrow pointing upward is
placed after the substance, or a horizontal line is drawn above the said substance. If a reactant or
product is appreciably water insoluble, an arrow pointing downward is placed after the symbol.
Questions and Problems
1. Dalton (whose symbols were quickly supplanted by those of Berzelius) raised the following
objection to the new symbols: “Berzelius’s symbols are horrifying; a young student in
chemistry might as soon learn Hebrew as make himself acquainted with them.” As a young
student in chemistry, do you agree?
2. Balance the following equations:
a) Experiment 4: Caustic soda (sodium hydroxide) plus muriatic (hydrochloric) acid yields table
salt (sodium chloride) and water.
NaOH + HCl = NaCl + H2O
191
(b) Experiments 2 and 4: Magnesium burnt in oxygen yields magnesium oxide.
Mg + O2 = MgO
(c) Proust’s green carbonate of copper.
Cu + O2 + CO2 + H2O = CuCO3Cu(OH)2 All one molecule.
(d) Experiment 4: Muriate of barites (barium chloride) plus sulfate of potash (potassium sulfate)
yield sulfate of barites (barium sulfate) and muriate of potash (potassium chloride).
BaCl2 + K2SO4 = BaSO4 + KCl
(e) Demonstration 10: Sodium metal dropped in water decomposes the water, yielding hydrogen
gas and caustic soda (sodium hydroxide).
Na + H2O = NaOH + H2
(f) Experiment 4: Calcium added to water yields calcium hydroxide and hydrogen gas.
Ca + H2O = CaO2H2 + H2
or = Ca(OH)2 + H2
Note that the first way of writing the product is more old-fashioned: It shows component
molecules. Whereas the second way designates the OH (or hydroxide) radical, as this usually
acts as a unit during chemical reactions. Analogously, sulfuric acid could be written as H2OSO3
(the old-fashioned way) or H2SO4.
Note: In some of the above molecular formulas (e.g., H2O, O2) we have accepted Avogadro’s
argument as correct. Which are the best-defined formulas for the above compounds and how one
defends such formulas will be dealt with shortly.
192
Pierre-Louis Dulong and Alexis-Thérèse Petit
Extracts from
“Researches on Certain Important Points about the Theory of Heat”1
Considerations founded upon the group of laws pertaining to the proportions of chemical
compounds now make it possible to form ideas about the constitution of bodies which, although
arbitrarily established in several points, nevertheless cannot be regarded as vague and absolutely
sterile speculations. Moreover, we are persuaded that certain properties of matter would present
themselves under more simple forms and would permit themselves to be expressed by more
regular and less complicated laws if one could relate them to the elements on which they
immediately depend. Accordingly, we have tried to introduce the most certain of the results of
the atomic theory into the study of a few of the properties that appear more intimately tied to the
individual action of the material molecules. The success that we have already obtained makes us
hope not only that considerations of this kind will be able to contribute powerfully to further
progress in physical science, but that the corpuscular theory will, in its turn, receive from them a
new degree of probability, and that it will discover sure means of discerning the truth when
different hypotheses seem equally plausible.
Among the properties of matter to which the considerations that we have just indicated
may be applied, we will first choose, as having especially fixed our attention, those which
depend on the action of heat. In directing our operations in a suitable manner, we have been led
to discover some simple relations between phenomena whose connection had not been perceived
before. However, as the numerous points of view under which these phenomena can be
considered give to the investigation which we have begun an extent which does not permit one to
include all their parts at the same time, we have thought it would be useful to make known at
present the results at which we have already arrived….
We shall now present in one table the specific heats of several elementary bodies,
limiting ourselves to those determinations about which we no longer feel any doubt.
1 [Recherches sur quelques points importants de la Théorie de la Chaleur, which appeared in Annales de Chimie et
de Physique, vol. 10 (1819).]
193
Specific Heats2
Relative
Weights of the
Atoms3
Product of the
Weight of Each
Atom Times the
Corresponding
Capacity Bismuth
0.0288
13.30
0.3830
Lead
0.0293
12.95
0.3794
Gold
0.0298
12.43
0.3704
Platinum
0.0314
11.164
0.3740
Tin
0.0514
7.35
0.3779
Silver
0.0557
6.75
0.3759
Zinc
0.0927
4.03
0.3736
Tellurium
0.0912
4.03
0.3675
Copper
0.0949
3.957
0.3755
Nickel
0.1035
3.69
0.3819
Iron
0.1100
3.392
0.3731
Cobalt
0.1498
2.46
0.3685
Sulfur
0.1880
2.011
0.3780
To make clear the law that we are about to announce, in the preceding table we have
added to the specific heats5 of various elementary substances the relative weights of their atoms.
These weights are derived, as is well known, from the ratios in which the weighable quantities of
elementary substances combine together. The care that for some years has been devoted to the
determination of the proportions of the constituents in the majority of chemical compounds
2 [The specific heat capacity of water is taken as 1.]
3 [The relative weight of the oxygen atom is taken as 1.]
4 [Apparently a misprint for 11.91.]
5 [Recall from the Measurement Manual that a heat capacity refers to the amount of heat, for example in calories,
required to raise or to lower the temperature of any weight body one degree (e.g., centigrade). A specific heat
capacity, or specific heat, refers to the amount of heat required to raise (or lower) the temperature of a given unit
weight (e.g., a gram) of a substance one degree.]
194
leaves very slight uncertainty in the values that we have used. However, as there exists no
rigorous means of ascertaining the actual number of atoms of each species that enter into a
combination, it is to be concluded that there is always some arbitrariness in fixing the specific
weight of elementary molecules; but the resulting uncertainty at most concerns only two or three
numbers that stand in the simplest ratios to one another. The reasons that have guided us in our
choice will be sufficiently explained by what follows. For the moment we will confine ourselves
to saying that none of the determinations we have arrived at are out of accord with the best-
established chemical analogies.
We can, by means of the figures contained in the preceding tables, now easily calculate
the ratios that exist between the capacities of atoms differing in kind. Let us note, therefore, that
to proceed from the specific heats furnished by observation to the specific heats of the particles
themselves it is but necessary to divide the former by the number of particles contained in equal
weights of the substances compared. Now it is obvious that these numbers of particles are, for
equal weights of matter, reciprocally proportional to the densities of the atoms.6 We arrive, then,
at the desired result by multiplying each [specific heat] capacity obtained by experiment by the
weight of the corresponding atom. It is these different products that have been arranged in the
last column of the table.
The very inspection of these numbers shows a comparison too remarkably simple not to
indicate immediately the existence of a physical law susceptible of being generalized and
extended to all elementary substances. In effect, the products in question, which express the
capacities of different atoms, approach equality to such a degree that it is impossible that the
very slight differences that are noticed are due to anything other than the inevitable errors either
in the measurement of the capacities or in the chemical analyses, especially if it is noticed that in
certain cases the errors arising from these two sources may be in the same direction and
consequently may be found multiplied in the result. The number and diversity of the substances
on which we have worked forbids considering the relation we have just indicated as simply
fortuitous, and the following law may be justly concluded:
Atoms of all simple substances have exactly the same capacity for heat.
In recalling what we have said previously concerning the kind of uncertainty that is still
attached to the fixation of the specific weights of atoms, it will easily be perceived that, should
one adopt a supposition regarding the density of the particles different from that which we have
made, the law which we have just established would be modified. But in every case, this law
will consist in the expression of a simple relation between the weights and the specific heats of
elementary atoms, and it is felt that, having to choose between equally probable hypotheses, we
ought to decide in favor of that which would establish the simplest relationship between the
elements compared.
Whatever the principle adopted on this relation, moreover, it may henceforth serve as a
control on the results of chemical analysis and, in certain cases, even offer the most exact means
of arriving at a knowledge of the proportions of certain combinations. But if, in the continuation
6 [Notice that Dulong and Petit speak of the densities of the atoms, not the densities of the bulk substances; they
seem to be referring to the (relative) weight per atom for a given substance. Whence Dulong and Petit speak of the
“densities of the atoms” and, in the next sentence, the “weight of the corresponding atom” as the same thing. Thus
they are really saying that for the same weight of two elements, the number of particles in one is to the number of
particles in the other as the atomic weight of the other is to the atomic weight of the one. Is this proportion
justifiable?]
195
of our work, no fact arises to weaken the probability of the opinion that we now prefer, it will be
found to much advantage to fix in a definite and uniform manner the specific weights of the
atoms of all simple substances that may be submitted to direct observation.
The law that we have just enunciated appears to be independent of the form of the
substances, provided, however, that they are considered in the same circumstances.
* * * * *
196
Stanislao Cannizzaro
Sketch of A Course of Chemical Philosophy1
[First Lecture]
I believe that the progress of science made in these last years has confirmed the hypothesis
of Avogadro, of Ampère, and of Dumas on the similar constitution of substances in the gaseous
state; that is, that equal volumes of these substances, whether simple or compound, contain an
equal number of molecules: not, however, an equal number of atoms, since the molecules of the
different substances, or those of the same substance in its different states,2 may contain a
different number of atoms, whether of the same or of a diverse nature.
In order to lead my students to the conviction that I have reached myself, I wish to place
them on the same path as that by which I have arrived at it—the path, that is, of the historical
examination of chemical theories.
I commence, then, in the first lecture by showing how, from the examination of the physical
properties of gaseous bodies, and from the law of Gay-Lussac on the volume relations between
components and compounds, there arose almost spontaneously the hypothesis alluded to above,
which was first of all enunciated by Avogadro, and shortly afterward by Ampère. Analyzing the
conception of these two physicists, I show that it contains nothing contradictory to known facts,
provided that we distinguish, as they did, molecules from atoms; provided that we do not confuse
the criteria by which the number and the weight of the former are compared, with the criteria that
serve to deduce the weight of the latter; and provided that, finally, we have not fixed in our
minds the prejudice that whilst the molecules of compound substances may consist of different
numbers of atoms, the molecules of the various simple substances must all contain either one
atom, or at least an equal number of atoms.
[Second Lecture]
In the second lecture I set myself the task of investigating the reasons why this hypothesis of
Avogadro and Ampère was not immediately accepted by the majority of chemists. I therefore
expound rapidly the work and ideas of those who examined the relationships of the reacting
quantities of substances without concerning themselves with the volumes that these substances
occupy in the gaseous state; and I pause to explain the ideas of Berzelius, by the influence of
which the hypothesis above cited appeared to chemists out of harmony with the facts.
I examine the order of the ideas of Berzelius, and show how, on the one hand, he developed
and completed the dualistic theory of Lavoisier by his own electro-chemical hypothesis, and
how, on the other hand, influenced by the atomic theory of Dalton (which had been confirmed by
the experiments of Wollaston), he applied this theory and took it for his guide in his later
1 [“Letter of Professor Stanislao Cannizzaro to Professor S. De Luca: Sketch of A Course of Chemical Philosophy,
Given in the Royal University of Genoa,” from Il Nuovo Cimento, vol. 7 (1858), pp. 321-366. Published as a
booklet in 1859.]
2 [See footnote 3.]
197
researches, bringing it into agreement with the dualistic electro-chemical theory, whilst at the
same time he extended the laws of Richter and tried to harmonize them with the results of Proust.
I bring out clearly the reason why he was led to assume that the atoms, whilst separate in simple
bodies, should unite to form the atoms of a compound of the first order, and these in turn, uniting
in simple proportions, should form composite atoms of the second order, and why (since he could
not admit that when two substances gave a single compound, a molecule of one and a molecule
of the other, instead of uniting to form a single molecule, should change into two molecules of
the same nature) he could not accept the hypothesis of Avogadro and Ampère, which in many
cases leads to the conclusion just indicated.
I then show how Berzelius, being unable to escape from his own dualistic ideas, and yet
wishing to explain the simple relations discovered by Gay-Lussac between the volumes of the
gaseous compounds and their gaseous components, was led to formulate a hypothesis very
different from that of Avogadro and of Ampère, namely, that equal volumes of simple substances
in the gaseous state contain the same number of atoms, which in combination unite intact; how,
later, the vapor densities of many simple substances having been determined, he had to restrict
this hypothesis by saying that only simple substances that are permanent gases obey this law;
how, not believing that composite atoms even of the same order could be equidistant in the
gaseous state under the same conditions, he was led to suppose that in the molecules of
hydrochloric, hydriodic, and hydrobromic acids, and in those of water and sulfuretted hydrogen,
there was contained the same quantity of hydrogen, although the different behavior of these
compounds confirmed the deductions from the hypothesis of Avogadro and Ampère.
I conclude this lecture by showing that we have only to distinguish atoms from molecules in
order to reconcile all the experimental results known to Berzelius, and have no need to assume
any difference in constitution between permanent and coercible, or between simple and
compound gases, in contradiction to the physical properties of all elastic fluids.
[Third Lecture]
In the third lecture I pass in review the various researches of physicists on gaseous bodies,
and show that all the new researches from Gay-Lussac to Clausius confirm the hypothesis of
Avogadro and of Ampère that the distances between the molecules, so long as they remain in the
gaseous state, do not depend on their nature, nor on their mass, nor on the number of atoms they
contain, but only on their temperature and on the pressure to which they are subjected.
[Fourth Lecture]
In the fourth lecture I pass under review the chemical theories since Berzelius: I pause to
examine how Dumas, inclining to the idea of Ampère, had habituated chemists who busied
themselves with organic substances to apply this idea in determining the molecular weights of
compounds; and what were the reasons that had stopped him half-way in the application of this
theory. I then expound, in continuation of this, two different methods—the one due to Berzelius,
the other to Ampère and Dumas—which were used to determine formulae in inorganic and in
organic chemistry respectively until Laurent and Gerhardt sought to bring both parts of the
science into harmony. I explain clearly how the discoveries made by Gerhardt, Williamson,
Hofmann, Wurtz, Bethollet, Frankland, and others on the constitution of organic compounds
198
confirm the hypothesis of Avogadro and Ampère, and how that part of Gerhardt’s theory that
corresponds best with the facts and best explains their connection is nothing but the extension of
Ampère’s theory, that is, its complete application, already begun by Dumas.
I draw attention, however, to the fact that Gerhardt did not always consistently follow the
theory that had given him such fertile results; since he assumed that equal volumes of gaseous
bodies contain the same number of molecules only in the majority of cases, but not always.
I show how he was constrained by a prejudice, the reverse of that of Berzelius, frequently to
distort the facts. Whilst Berzelius, on the one hand, did not admit that the molecules of simple
substances could be divided in the act of combination, Gerhardt supposes that all the molecules
of simple substances are divisible in chemical action. This prejudice forces him to suppose that
the molecule of mercury and of all the metals consists of two atoms, like that of hydrogen, and
therefore that the compounds of all the metals are of the same type as those of hydrogen. This
error even yet persists in the minds of chemists, and has prevented them from discovering
amongst the metals the existence of biatomic radicals perfectly analogous to those lately
discovered by Wurtz in organic chemistry.
From the historical examination of chemical theories, as well as from physical researches, I
draw the conclusion that to bring into harmony all the branches of chemistry we must have
recourse to the complete application of the theory of Avogadro and Ampère in order to compare
the weights and the numbers of the molecules; and I propose in the sequel to show that the
conclusions drawn from it are invariably in accordance with all physical and chemical laws
hitherto discovered.
[Fifth Lecture]
I begin in the fifth lecture by applying the hypothesis of Avogadro and Ampère to determine
the weights of molecules even before their composition is known.
On the basis of the hypothesis cited above, the weights of the molecules are proportional to
the densities of the substances in the gaseous state. If we wish the densities of vapors to express
the weights of the molecules, it is expedient to refer them all to the density of a simple gas taken
as unity, rather than to the weight of a mixture of two gases, such as air.
Hydrogen being the lightest gas, we may take it as the unit to which we refer the densities of
other gaseous bodies, which in such a case express the weights of the molecules compared to the
weight of the molecule of hydrogen = 1.
Since I prefer to take as common unit for the weights of the molecules and for their
fractions, the weight of a half and not of a whole molecule of hydrogen, I therefore refer the
densities of the various gaseous bodies to that of hydrogen = 2. If the densities are referred to air
= 1, it is sufficient to multiply by 14.438 to change them to those referred to that of hydrogen =
1; and by 28.87 to refer them to the density of hydrogen = 2.
I write the two series of numbers, expressing these weights in the following manner:
199
Names of Substances
Densities or weights of one volume,
the volume of Hydrogen being
made = 1, i.e., the weights of a
whole molecule of Hydrogen taken
as unity
Densities referred to that of
Hydrogen = 2, i.e., weights of the
molecules referred to the weight
of half a molecule of Hydrogen
taken as unity
Hydrogen
1
2
Oxygen, ordinary
16
32
Oxygen, electrised
64
128
Sulfur below 1000 ºC
96
192
Sulfur* above 1000 ºC
32
64
Chlorine
35.5
71
Bromine
80
160
Arsenic
150
300
Mercury
100
200
Water
9
18
Hydrochloric Acid
18.25
36.50†
Acetic Acid
30
60
*This determination was made by Bineau, but I believe it requires confirmation.
†The numbers expressing the densities are approximate: We arrive at a closer approximation by comparing
them with those derived from chemical data, and bringing the two into harmony.
Whoever wishes to refer the densities to hydrogen = 1 and the weights of the molecules to
the weight of half a molecule of hydrogen, can say that the weights of the molecules are all
represented by the weight of two volumes.
I myself, however, for simplicity of exposition, prefer to refer the densities to that of
hydrogen = 2, and so the weights of the molecules are all represented by the weight of one
volume.
From the few examples contained in the table, I show that the same substance in its different
allotropic3 states can have different molecular weights, without concealing the fact that the
experimental data on which this conclusion is founded still require confirmation.
I assume that the study of the various compounds has been begun by determining the
weights of the molecules, i.e., their densities in the gaseous state, without inquiring if they are
3 [Different forms of the same element existing in the same state (solid, liquid, or gas) are known as allotropic
forms, or allotropes. Allotropy is exhibited by a number of elements, especially nonmetals. Oxygen and ozone
(electrised oxygen) are allotropes. Sulfur and phosphorous each have several allotropic forms.]
200
simple or compound.
I then come to the examination of the composition of these molecules. If the substance is
undecomposable, we are forced to admit that its molecules are made up by weight of one and the
same kind of matter. If the body is composite, its elementary analysis is made, and thus we
discover the constant relations between the weights of its components contained; then the weight
of the molecule is divided into parts proportional to the numbers expressing the relative weights
of the components contained in the molecule of the compound, referred to the same unit as that
to which we refer the weights of all the molecules. By this method I have constructed the
following table:
Name of Substance
Weight of one volume, i.e.,
weight of the molecule
referred to the weight of half
a molecule of Hydrogen = 1
Component weights of one volume, i.e.,
component weights of the molecule, all
referred to the weight of half a molecule
of Hydrogen = 1 Hydrogen
2
2 Hydrogen
Oxygen, ordinary
32
32 Oxygen
Oxygen, electrised
128
128 Oxygen
Sulfur below 1000 ºC
192
192 Sulfur
Sulfur above 1000 ºC(?)4
64
64 Sulfur
Phosphorous
124
124 Phosphorous
Chlorine
71
71 Chlorine
Bromine
160
160 Bromine
Iodine
254
254 Iodine
Nitrogen
28
28 Nitrogen
Arsenic
300
300 Arsenic
Mercury
200
200 Mercury
Hydrochloric acid
36.5
35.5 Chlorine, 1 Hydrogen
Hydrobromic acid
81
80 Bromine, 1 Hydrogen
Hydriodic acid
128
127 Iodine, 1 Hydrogen
Water
18
16 Oxygen, 2 Hydrogen
4 [This question mark is in the original, perhaps indicating (as in the previous table) that there is some uncertainty
about the vapor density at this temperature.]
201
Name of Substance
Weight of one volume, i.e.,
weight of the molecule
referred to the weight of half
a molecule of Hydrogen = 1
Component weights of one volume, i.e.,
component weights of the molecule, all
referred to the weight of half a molecule
of Hydrogen = 1
Ammonia 17 14 Nitrogen, 3 Hydrogen Arseniuretted Hydrogen
78
75 Arsenic, 3 Hydrogen
Phosphuretted Hydrogen
35
32 Phosphorous,5 3 Hydrogen
Calomel
235.5
35.5 Chlorine, 200 Mercury
Corrosive Sublimate
271
71 Chlorine, 200 Mercury
Arsenic Trichloride
181.5
106.5 Chlorine, 75 Arsenic
Protochloride of
Phosphorous
138.5
106.5 Chlorine, 32 Phosphorous
Perchloride of Iron
325
213 Chlorine, 112 Iron
Protoxide of Nitrogen
44
16 Oxygen, 28 Nitrogen
Binoxide of Nitrogen
30
16 Oxygen, 14 Nitrogen
Carbonic Oxide
28
16 Oxygen, 12 Carbon
Carbonic Acid
44
32 Oxygen, 12 Carbon
Ethylene
28
4 Hydrogen, 24 Carbon
Propylene
42
6 Hydrogen, 36 Carbon
Acetic Acid, hydrated
60
4 Hydrogen, 32 Oxygen, 24 Carbon
Acetic Acid, anhydrous
102
6 Hydrogen, 48 Oxygen, 48 Carbon
Alcohol
46
6 Hydrogen, 16 Oxygen, 24 Carbon
Ether
74
10 Hydrogen, 16 Oxygen, 48 Carbon
All the numbers contained in the preceding table are comparable among themselves, being
referred to the same unit. And to fix this well in the minds of my pupils, I have recourse to a very
simple artifice: I say to them, namely, “Suppose it to be shown that the half molecule of
hydrogen weighs a millionth of a milligram, then all the numbers of the preceding table become
concrete numbers, expressing in millionths of a milligram the concrete weights of the molecules
5 [Although the atomic weight of phosphorus implied in this and the protochloride of phosphorus is 32, this quantity
does not evenly divide the above molecular weight of phosphorus. Does a submultiple of it? If not, is this a problem
for Cannizzaro’s method?]
202
and of their components; the same thing would follow if the common unit had any other concrete
value,” and so I lead them to gain a clear conception of the comparability of these numbers,
whatever be the concrete value of the common unit.
Once this artifice has served its purpose, I hasten to destroy it by explaining how it is not
possible in reality to know the concrete value of this unit; but the clear ideas remain in the minds
of my pupils, whatever may be their degree of mathematical knowledge. I proceed pretty much as
engineers do when they destroy the wooden scaffolding that has served them to construct their
bridges, as soon as these can support themselves. But I fear that you will say, “Is it worth the
trouble and the waste of time and ink to tell me of this very common artifice?” I am, however,
constrained to tell you that I have become attached to this pedagogic expedient, having had such
great success with it amongst my pupils, and thus I recommend it to all those who, like myself,
must teach chemistry to youths not well accustomed to the comparison of quantities.
Once my students have become familiar with the importance of the numbers as they are
exhibited in the preceding table, it is easy to lead them to discover the law that results from their
comparison. “Compare,” I say to them, “the various quantities of the same element contained in
the molecule of the free substance and in those of all its different compounds, and you will not be
able to escape the following law: The different quantities of the same element contained in
different molecules are all whole multiples of one and the same quantity, which, always being
entire, has the right to be called an atom.”
Thus:
One molecule of free hydrogen contains 2 of hydrogen = 2 x 1
“ of hydrochloric acid “ 1 = 1 x 1
“ of hydrobromic acid “ 1 = 1 x 1
“ of hydriodic acid “ 1 = 1 x 1
“ of hydrocyanic acid “ 1 = 1 x 1
“ of water “ 2 = 2 x 1
“ of sulfuretted hydrogen “ 2 = 2 x 1
“ of formic acid “ 2 = 2 x 1
“ of ammonia “ 3 = 3 x 1
“ of gaseous phosphuretted hydrogen “ 3 = 3 x 1
“ of acetic acid “ 4 = 4 x 1
“ of ethylene “ 4 = 4 x 1
“ of alcohol “ 6 = 6 x 1
“ of ether “ 10 = 10 x 1
Thus all the various weights of hydrogen contained in the different molecules are integral
multiples of the weight contained in the molecule of hydrochloric acid, which justifies our having
taken it as common unit of the weights of the atoms and of the molecules. The atom of hydrogen
is contained twice in the molecule of free hydrogen.
In the same way it is shown that the various quantities of chlorine existing in different
molecules are all whole multiples of the quantity contained in the molecule of hydrochloric acid,
that is, of 35.5; and that the quantities of oxygen existing in the different molecules are all whole
multiples of the quantity contained in the molecule of water, that is, of 16, which quantity is half
203
of that contained in the molecule of free oxygen, and an eighth part of that contained in the
molecule of electrised oxygen (ozone).6
Thus:
One molecule of free oxygen contains 32 of oxygen = 2 x 16
One molecule of ozone contains 128 of oxygen = 8 x 16
One molecule of water contains 16 of oxygen = 1 x 16
One molecule of ether contains 16 of oxygen = 1 x 16
One molecule of acetic acid contains 32 of oxygen = 2 x 16
etc.
One molecule of free chlorine contains 71 of chlorine = 2 x 35.5
One molecule of hydrochloric acid contains 35.5 of chlorine = 1 x 35.5
One molecule of corrosive sublimate contains 71 of chlorine = 2 x 35.5
One molecule of chloride of arsenic contains 106.5 of chlorine = 3 x 35.5
One molecule of chloride of tin contains 142 of chlorine = 4 x 35.5
etc.
In a similar way may be found the smallest quantity of each element that enters as a whole
into the molecules that contain it, and to which may be given with reason the name of atom. In
order, then, to find the atomic weight of each element, it is necessary first of all to know the
weights of all or of the greater part of the molecules in which it is contained and their
composition.
If it should appear to any one that this method of finding the weights of molecules is too
hypothetical, then let him compare the composition of equal volumes of substances in the
gaseous state under the same conditions. He will not be able to escape the following law: The
various quantities of the same element contained in equal volumes either of the same element or
of its compounds are all whole multiples of one and the same quantity; that is, each element has a
special numerical value by means of which and of integral coefficients the composition by
weight of equal volumes of the different substances in which it is contained may be expressed.
Now, since all chemical reactions take place between equal volumes, or integral multiples of
them, it is possible to express all chemical reactions by means of the same numerical values and
integral coefficients. The law enunciated in the form just indicated is a direct deduction from the
facts: but who is not led to assume from this same law that the weights of equal volumes
represent the molecular weights, although other proofs are wanting? I thus prefer to substitute in
the expression of the law the word molecule instead of volume. This is advantageous for
teaching, because, when the vapor densities cannot be determined, recourse is had to other means
for deducing the weights of the molecules of compounds. The whole substance of my course
consists in this: to prove the exactness of these latter methods by showing that they lead to the
same results as the vapor density when both kinds of method can be adopted at the same time for
determining molecular weights.
6 [Ozone is an unstable form of oxygen often produced in large quantities by lightning and in smaller ones by
electric sparks, and had been discovered and identified by 1840. Its name is taken from the Greek (ozein),
meaning “to be odorous,” from its distinctive smell. Cannizzaro’s method would indicate that the molecule of ozone
is O8; it turned out later to be O3.]
204
The law enunciated above, called by me the law of atoms, contains in itself that of multiple
proportions and that of simple relations between the volumes; which I demonstrate amply in my
lecture. After this I easily succeed in explaining how, expressing by symbols the different atomic
weights of the various elements, it is possible to express by means of formulae the composition
of their molecules and of those of their compounds, and I pause a little to make my pupils
familiar with the passage from gaseous volume to molecule, the first directly expressing the fact
and the second interpreting it. Above all, I study to implant in their minds thoroughly the
difference between molecule and atom. It is possible indeed to know the atomic weight of an
element without knowing its molecular weight; this is seen in the case of carbon. A great number
of the compounds of this substance being volatile, the weights of the molecules and their
composition may be compared, and it is seen that the quantities of carbon that they contain are all
integral multiples of 12, which quantity is thus the atom of carbon and expressed by the symbol
C; but since we cannot determine the vapor density of free carbon7 we have no means of knowing
the weight of its molecule, and thus we cannot know how many times the atom is contained in it.
Analogy does not in any way help us, because we observe that the molecules of the most closely
analogous substances (such as sulfur and oxygen), and even the molecules of the same substance
in its allotropic states, are composed of different numbers of atoms. We have no means of
predicting the vapor density of carbon; the only thing that we can say is that it will be either 12 or
an integral multiple of 12 (in my system of numbers). The number that is given in different
treatises on chemistry as the theoretical density of carbon is quite arbitrary, and a useless datum
in chemical calculations; it is useless for calculating and verifying the weights of the molecules
of the various compounds of carbon, because the weight of the molecule of free carbon may be
ignored if we know the weights of the molecules of all its compounds; it is useless for
determining the weight of the atom of carbon, because this is deduced by comparing the
composition of a certain number of molecules containing carbon, and the knowledge of the
weight of the molecule of this last would scarcely add a datum more to those that are already
sufficient for the solution of the problem. Anyone will easily convince himself of this by placing
in the following manner the numbers expressing the molecular weights derived from the densities
and the weights of the components contained in them:
Names of
compounds of
Carbon
Weights of the
Molecules referred to
the atom of Hydrogen
Weights of the components of the
molecules referred to the weight of
the atom of Hydrogen taken as
unity
Formulae, making
H = 1; C = 12; O =
16; S = 32
Carbonic Oxide
28
12 Carbon, 16 Oxygen
CO
Carbonic Acid
44
12 Carbon, 32 Oxygen
CO2
Sulfide of Carbon 76
12 Carbon, 64 Sulfur
CS2
Marsh Gas8 16
12 Carbon, 4 Hydrogen
CH4
7 [Carbon sublimes at 4800°C.]
8 [Methane gas, the natural gas most frequently used for household heating and cooking.]
205
Names of
compounds of
Carbon
Weights of the
Molecules referred to
the atom of Hydrogen
Weights of the components of the
molecules referred to the weight of
the atom of Hydrogen taken as
unity
Formulae, making
H = 1; C = 12; O =
16; S = 32
Ethylene 28 24 Carbon, 4 Hydrogen C2H4 Propylene
42
36 Carbon, 6 Hydrogen
C3H6
Ether
Etc.
74
Etc.
48 Carbon, 10 Hydrogen, 16
Oxygen
Etc.
C4H10O
Etc.
_ _ _ _ .
In the list of molecules containing carbon there might be placed also that of free carbon if the
weight of it were known; but this would not have any greater utility than what we would derive
by writing in the list one more compound of carbon; that is, it would do nothing but verify once
more that the quantity of carbon contained in any molecule, whether of the element itself or of its
compounds, is 12 or n x 12 = Cn, n being an integral number.
I then discuss whether it is better to express the composition of the molecules of compounds
as a function of the molecules of the components, or if, on the other hand, it is better, as I
commenced by doing, to express the composition of both in terms of those constant quantities
that always enter by whole numbers into both, that is, by means of the atoms. Thus, for example,
is it better to indicate in the formula that one molecule of hydrochloric acid contains the weight
of half a molecule of hydrogen and half a molecule of chlorine, or that it contains an atom of one
and an atom of the other, pointing out at the same time that the molecules of both of these
substances consist of two atoms?
Should we adopt the formulae made with symbols indicating the molecules of the elements,
then many coefficients of these symbols would be fractional, and the formula of a compound
would indicate directly the ratio of the volumes occupied by the components and by the
compounds in the gaseous state. This was proposed by Dumas in his classical memoir, Sur
quelques points de la Théorie atomique (Annales de Chimie et de Physique, tom. 33, 1826).
To discuss the question proposed, I give to the molecules of the elements symbols of a
different kind from those employed to represent the atoms, and in this way I compare the
formulae made with the two kinds of symbols:
Atoms or Molecules
Symbols of the molecules
of the Elements and
formulae made with these
symbols9
Symbols of the atoms of
the Elements and formulae
made with these symbols
Numbers
expressing their
weight
Atom of Hydrogen
H 1/2
H
1
Molecule of Hydrogen
H
H2
2
9 [The font we are using to indicate Cannizzaro’s notation following molecules is not identical to his, but merely
similar.]
206
Atoms or Molecules
Symbols of the molecules
of the Elements and
formulae made with these
symbols9
Symbols of the atoms of
the Elements and formulae
made with these symbols
Numbers
expressing their
weight
Atom of Oxygen
O 1/2 = Oz
1/8
O
16
Molecule of Ordinary
Oxygen
O
O2
32
Molecule of
Electricised Oxygen
(Ozone)
Oz
O8
128
Atom of Sulfur
S 1/2 = Sa 1/6
S
32
Molecule of Sulfur
(1000°+)
S
S2
64
Molecule of Sulfur
(1000° & -)
Sa
S6
192
Molecule of Water
HO 1/2 = HOz 1/8
H2O
18
Molecule of
Sulfurretted Hydrogen
HS 1/2 = HSa
1/6
H2S
34
These few examples are sufficient to demonstrate the inconveniences associated with the
formulae indicating the composition of compound molecules as a function of the entire
component molecules, which may be summed up as follows:
1. It is not possible to determine the weight of the molecules of many elements the density
of which in the gaseous state cannot be ascertained.
2. If it is true that oxygen and sulfur have different densities in their different allotropic
states, that is, if they have different molecular weights, then their compounds would have two or
more formulae according as the quantities of their components were referred to the molecules of
one or the other allotropic state.
3. The molecules of analogous substances (such as sulfur and oxygen) being composed of
different numbers of atoms, the formulae of analogous compounds would be dissimilar. If we
indicate, instead, the composition of the molecules by means of the atoms, it is seen that
analogous compounds contain in their molecules an equal number of atoms.
It is true that when we employ in the formulae the symbols expressing the weights of the
molecules, i.e., of equal volumes, the relationship between the volumes of the components and
those of the compounds follows directly; but this relationship is also indicated in the formulae
expressing the number of atoms; it is sufficient to bear in mind that the atom represented by a
symbol is either the entire molecule of the free substance or a fraction of it, that is, it is sufficient
to know the atomic formula of the free molecule. Thus, to take an example, it is sufficient to
know that the atom of oxygen, O, is one-half of the molecule of ordinary oxygen and an eighth
207
part of the molecule of electrised oxygen—to know that the weight of the atom of oxygen is
represented by 1/2 volume of free oxygen and 1/8 of electrised oxygen. In short, it is easy to
accustom students to consider the weights of the atoms as being represented either by a whole
volume or by a fraction of a volume, according as the atom is equal to the whole molecule or to a
fraction of it. In this system of formulae, those which represent the weights and the composition
of the molecules, whether of elements or of compounds, represent the weights and the
composition of equal gaseous volumes under the same conditions. The atom of each element is
represented by that quantity of it that constantly enters as a whole into equal volumes of the free
substance or of its compounds; it may be either the entire quantity contained in one volume of the
free substance or a simple sub-multiple of this quantity.
[Sixth Lecture]
This foundation of the atomic theory having been laid, I begin in the following lecture—the
sixth—to examine the constitution of the molecules of the chlorides, bromides, and iodides.
Since the greater part of these are volatile, and since we know their densities in the gaseous state,
there cannot remain any doubt as to the approximate weights of the molecules and so of the
quantities of chlorine, bromine, and iodine contained in them. These quantities being always
integral multiples of the weights of chlorine, bromine, and iodine contained in hydrochloric,
hydrobromic, and hydriodic acids, i.e., of the weights of the half molecules, there can remain no
doubt as to the atomic weights of these substances, and thus as to the number of atoms existing in
the molecules of their compounds, whose weights and compositions are known.
A difficulty sometimes appears in deciding whether the quantity of the other element
combined with one atom of these halogens10 is 1, 2, 3, or n atoms in the molecule; to decide this,
it is necessary to compare the composition of all the other molecules containing the same element
and find out the weight of this element that constantly enters as a whole. When we cannot
determine the vapor densities of the other compounds of the element whose atomic weight we
wish to determine, it is necessary then to have recourse to other criteria to know the weights of
their molecules and to deduce the weight of the atom of the element.
What I am to expound in the sequel serves to teach my pupils the method of employing these
other criteria to verify or to determine atomic weights and the composition of molecules. I begin
by making them study the following table of some chlorides, bromides, and iodides whose vapor
densities are known; I write their formulae, certain of justifying later the value assigned to the
atomic weights of some elements existing in the compounds indicated. I do not omit to draw their
attention once more to the atomic weights of hydrogen, chlorine, bromine, and iodine, being all
equal to the weights of half a molecule, and represented by the weight of half a volume, which I
indicate in the following table:
10
[Recall that halogens (from halys, meaning “salt”) are elements that combine with other radicals—usually
metals—to form salts. This is what the “analogy” among these elements consists in.]
208
Symbol
Weight
Weight of the atom of Hydrogen or half a molecule
represented by the weight of ½ a volume
H
1
Weight of the atom of Chlorine or half a molecule
represented by the weight of ½ volume
Cl
35.5
Weight of the atom of Bromine or half a molecule
represented by the weight of ½ volume
Br
80
Weight of the atom of Iodine or half a molecule
represented by the weight of ½ volume
I
127
These data being given, there follows the table of some compounds of the halogens:
Names of the
Chlorides
Weights of equal
volumes in the gaseous
state, under the same
conditions, referred to
the weight of ½ volume
of Hydrogen = 1; i.e.,
weights of the
molecules referred to
the weight of the atom
of Hydrogen = 1
Composition of equal volumes
in the gaseous state, under the
same conditions, i.e.,
composition of the molecules,
the weights of the components
being all referred to the weight
of the atom of Hydrogen taken
as unity, i.e., the common unit
adopted for the weights of
atoms and molecules
Formulae
expressing the
composition of
the molecules or
of equal volumes
in the gaseous
state under the
same conditions
Free Chlorine
71
71 Chlorine
Cl2
Hydrochloric Acid
36.5
35.5 Cl, 1 Hydrogen
HCl
Protochloride of
Mercury (Calomel)
235.5
35.5 Cl, 200 Mercury
HgCl
Bichloride of Mercury,
or Corrosive Sublimate
271
71 Cl, 200 Mercury
HgCl2
Chloride of Ethyl
64.5
35.5 Cl, 5 H, 24 C
C2H5Cl
Chloride of Acetyl
78.5
35.5 Cl, 24 C, 3 H, 16 O
C2H3OCl
Chloride of Ethylene
99
71 Cl, 4 H, 24 C
C2H4Cl2
209
Names of the
Chlorides
Weights of equal
volumes in the gaseous
state, under the same
conditions, referred to
the weight of ½ volume
of Hydrogen = 1; i.e.,
weights of the
molecules referred to
the weight of the atom
of Hydrogen = 1
Composition of equal volumes
in the gaseous state, under the
same conditions, i.e.,
composition of the molecules,
the weights of the components
being all referred to the weight
of the atom of Hydrogen taken
as unity, i.e., the common unit
adopted for the weights of
atoms and molecules
Formulae
expressing the
composition of
the molecules or
of equal volumes
in the gaseous
state under the
same conditions
Chloride of Arsenic 181.5 106.5 Cl, 75 Arsenic AsCl3 Protochloride of
Phosphorus
138.5
106.5 Cl, 32 Phosphorus
PCl3
Chloride of Boron
117.5
106.5 Cl, 11 Boron
BCl3
Bichloride of Tin
259.6
142 Cl, 117.6 Tin
SnCl4
Bichloride of Titanium
198
142 Cl, 56 Titanium
TiCl4
Chloride of Silicon
170
142 Cl, 28 Silicon
SiCl4
Chloride of Zirconium
231
142 Cl, 89 Zirconium
ZrCl4
Chloride of Aluminum
267
213 Cl, 54 Aluminium
Al2Cl6
Perchloride of Iron
325
213 Cl, 112 Iron
Fe2Cl6
Sesquichloride of
Chromium
319
213 Cl, 106 Chromium
Cr2Cl6
I stop to examine the composition of the molecules of the two chlorides and the two iodides
of mercury. There can remain no doubt that the protochloride contains in its molecule the same
quantity of chlorine as hydrochloric acid, that the bichloride contains twice as much, and that the
quantity of mercury contained in the molecules of both is the same. The supposition made by
some chemists that the quantities of chlorine contained in the two molecules are equal, and on the
other hand that the quantities of mercury are different, is supported by no valid reason. The vapor
densities of the two chlorides having been determined, and it having been observed that equal
volumes of them contain the same quantity of mercury, and that the quantity of chlorine
contained in one volume of the vapor of calomel is equal to that contained in the same volume of
hydrochloric acid gas under the same conditions, whilst the quantity of chlorine contained in one
volume of corrosive sublimate is twice that contained in an equal volume of calomel or of
hydrochloric acid gas, the relative molecular composition of the two chlorides cannot be
doubtful. The same may be said of the two iodides. Does the constant quantity of mercury
existing in the molecules of these compounds, and represented by the number 200, correspond to
one or more atoms? The observation that in these compounds the same quantity of mercury is
combined with one or two atoms of chlorine or of iodine, would itself incline us to believe that
210
this quantity is that which enters always as a whole into all the molecules containing mercury,
namely, the atom; whence Hg = 200.
To verify this, it would be necessary to compare the various quantities of mercury contained
in all the molecules of its compounds whose weights and composition are known with certainty.
Few other compounds of mercury besides those indicated above lend themselves to this; still
there are some in organic chemistry the formulae of which express well the molecular
composition; in these formulae we always find Hg2 = 200, chemists having made Hg = 100 and
H = 1. This is a confirmation that the atom of mercury is 200 and not 100, no compound of
mercury existing whose molecule contains less than this quantity of it. For verification I refer to
the law of the specific heats of elements and of compounds.11
I call the “quantity of heat” consumed by the atoms, or the molecules, the product of their
weights into their specific heats. I compare the heat consumed by the atom of mercury with that
consumed by the atoms of iodine and of bromine in the same physical state, and find them
almost equal, which confirms the accuracy of the relation between the atomic weight of mercury
and that of each of the two halogens, and thus also, indirectly, between the atomic weight of
mercury and that of hydrogen, whose specific heats cannot be directly compared.
Thus we have:
Name of Substance
Atomic
Weight
Specific Heat—Heat
required to heat unit
weight 1 ºC
Products of specific heats by atomic
weight—Heat required to heat the
atom 1 ºC Solid Bromine
80
0.08432
6.74560
Iodine
127
0.05412
6.87324
Solid Mercury
200
0.03241
6.48200
The same thing is shown by comparing the specific heats of the different compounds of
mercury. Woestyn and Garnier have shown that the state of combination does not notably change
the calorific capacity of the atoms; and since this is almost equal in the various elements, the
molecules would require, to heat them 1º, quantities of heat proportional to the number of atoms
that they contain. If Hg = 200, that is, if the formulae of the two chlorides and iodides of mercury
are HgCl, HgI, HgCl2, HgI2, it will be necessary that the molecules of the first pair should
consume twice as much heat as each separate atom, and those of the second pair three times as
much; and this is so in fact, as may be seen in the following table:
11
[This is of course referring to the law discovered by Dulong and Petit. The quantity of heat “consumed by” the
atom is what they called the “heat capacity” of the atom.]
211
Formulae of
the
compounds of
mercury
Weights of
their
molecules
= p
Specific heats
of unit weight
= c
Specific heats of
the molecules
= p x c
Number of atoms
in the molecules
= n
Specific heats
of each atom
= p x c/n
HgCl
235.5
0.05205
12.257745
2
6.128872
HgI
327
0.03949
12.91323
2
6.45661
HgCl2
271
0.06889
18.66919
3
6.22306
HgI2
454
0.04197
19.05438
3
6.35146
Thus the weight 200 of mercury, whether as an element or in its compounds, requires to heat
it 1º the same quantity of heat as 127 of iodine, 80 of bromine, and almost certainly as 35.5 of
chlorine and 1 of hydrogen, if it were possible to compare these two last substances in the same
physical state as that in which the specific heats of the above named substances have been
compared.
But the atoms of hydrogen, iodine, and bromine are half their respective molecules: Thus it
is natural to ask whether the weight 200 of mercury also corresponds to half a molecule of free
mercury. It is sufficient to look at the table of numbers expressing the molecular weights to
perceive that if 2 is the molecular weight of hydrogen, the weight of the molecule of mercury is
200, i.e., equal to the weight of the atom. In other words, one volume of vapor, whether of
protochloride or protoiodide, whether of bichloride or of biniodide, contains an equal volume of
mercury vapor; so that each molecule of these compounds contains an entire molecule of
mercury, which, entering as a whole into all the molecules, is the atom of this substance. This is
confirmed by observing that the complete molecule of mercury requires for heating it 1º, the
same quantity of heat as half a molecule of iodine, or half a molecule of bromine. It appears to
me, then, that I can sustain that what enters into chemical actions is the half molecule of
hydrogen and the whole molecule of mercury: Both of these quantities are indivisible, at least in
the sphere of chemical reactions currently known. You will perceive that with this last expression
I avoid the question if it is possible to divide this quantity further. I do not fail to apprise you that
all those who faithfully applied the theory of Avogadro and of Ampére have arrived at this same
result. First, Dumas and afterwards Gaudin showed that the molecule of mercury, differing from
that of hydrogen, always entered as a whole into compounds. On this account Gaudin called the
molecule of mercury monatomic, and that of hydrogen biatomic. However, I wish to avoid the
use of these adjectives in this special sense, because today they are employed, as you know, in a
very different sense, that is, to indicate the different capacity for saturation of the radicals.12
The formulae of the two chlorides of mercury having been demonstrated, I next compare
them with that of hydrochloric acid. The atomic formulae indicate that the constitution of the
protochloride is similar to that of hydrochloric acid, if we consider the number of atoms existing
in the molecules of the two: If, however, we compare the quantities of the components with those
that exist in their free molecules, then a difference is perceived.
12
[This use of terms was at the time being followed by Gerhardt, Dumas, and others using a “system of types,”
which we will consider shortly.]
212
To make this evident I bring the atomic formulae of the various molecules under examination
into comparison with the formulae made with the symbols expressing the weights of the entire
molecules, placing them in the manner that you see below:
Symbols of the Molecules of the
elements and formulae of their
compounds made with these
symbols, i.e., symbols and formulae
representing the weights of equal
volumes in the gaseous state
Symbols of the
Atoms of the
elements, and
formulae of their
compounds made
with these symbols
Numbers
expressing
their
corresponding
weights
Atom of Hydrogen
H 1/2
H
1
Molecule of Hydrogen
H
H2
2
Atom of Chlorine
Cl 1/2
Cl
35.5
Molecule of Chlorine
Cl
Cl2
71
Atom of Bromine
Br 1/2
Br
80
Molecule of Bromine
Br
Br2
160
Atom of Iodine
I 1/2
I
127
Molecule of Iodine
I
I2
254
Atom of Mercury
Hg
Hg
200
Molecule of Mercury
Hg
Hg
200
Molecule of
Hydrochloric Acid
H 1/2 Cl 1/2
HCl
36.5
Molecule of
Hydrobromic Acid
H 1/2 Br 1/2
HBr
81
Molecule of
Hydroiodic Acid
H 1/2 I 1/2
HI
128
Molecule of
Protochloride of
Mercury
HgCl 1/2
HgCl
235.5
Molecule of
Protobromide of
Mercury
HgBr 1/2
HgBr
280
Molecule of
Protoiodide of Mercury
HgI 1/2
HgI
327
213
Symbols of the Molecules of the
elements and formulae of their
compounds made with these
symbols, i.e., symbols and formulae
representing the weights of equal
volumes in the gaseous state
Symbols of the
Atoms of the
elements, and
formulae of their
compounds made
with these symbols
Numbers
expressing
their
corresponding
weights
Molecule of Bichloride
of Mercury
HgCl
HgCl2
271
Molecule of Bibromide
of Mercury
HgBr
HgBr2
360
Molecule of Biniodide
of Mercury
HgI
HgI2
454
The comparison of these formulae confirms still more the preference that we must give to
the atomic formulae, which indicate also clearly the relations between the gaseous bodies. It is
sufficient to recall that whilst the atoms of chlorine, bromine, iodine, and hydrogen are
represented by the weight of 1/2 volume, the atom of mercury is represented by the weight of a
whole volume.13
I then come to the examination of the two chlorides of copper. The analogy with those of
mercury leads us to suppose that they have a similar atomic constitution, but we cannot verify
this directly by determining and comparing the weights and the compositions of the molecules, as
we do not know the vapor densities of these two compounds.
The specific heats of free copper and of its compounds confirm the atomic constitution of
the two chlorides of copper deduced from the analogy with those of mercury. Indeed, the
composition of the two chlorides leads us to conclude that if they have the formulae CuCl, CuCl2,
the atomic weight of copper indicated by Cu is equal to 63, which may be seen from the
following proportions:
Ratio between the components
expressed by numbers whose sum = 100
Ratio between the components
expressed by atomic weights Protochloride of Copper
36.04 Cl : 63.96 Cu
35.5 Cl : 63 Cu
Bichloride of Copper
52.98 Cl : 47.02 Cu
71 Cl : 63 Cu
Now 63 multiplied by the specific heat of copper gives a product practically equal to that
given by the atomic weight of iodine or of mercury into their respective specific heats. Thus:
63 x 0.09515 = 6 Atomic weight Specific heat
of copper of copper
13
[It is worth noting that, by arguing that the molecule of mercury (and later, that of other metals) is the same as the
atom of mercury, Cannizzaro is implicitly modifying Avogadro’s hypothesis that all substances in the elastic state
are diatomic.]
214
The same quantity of heat is required to heat the weight of 63 of copper in its compounds
through 1º. Thus:
Formulae
of the compounds
of copper
Weights of their
molecules
= p
Specific heats of
unit weights
= c
Specific heats of
the molecules
= p x c
Number of atoms
in the molecules
= n
Specific heat of
each atom
= p x c/n
CuCl
98.5
0.13817
13.619595
2
6.809797
CuI
190
0.06869
14.0511
2
7.0255
After this comes the question whether this quantity of copper that enters as a whole into the
compounds, the calorific capacity of the atoms being maintained, is an entire molecule or a sub-
multiple of it. The analogy of the compounds of copper with those of mercury would make us
inclined to believe that the atom of copper is a complete molecule. But having no other proof to
confirm this, I prefer to declare that there is no means of knowing the molecular weight of free
copper until the vapor density of this substance can be determined.
I then go on to examine the constitution of the chlorides, bromides, and iodides of
potassium, sodium, lithium, and silver. Each of these metals makes with each of the halogens
only one well characterized and definite compound; of none of these compounds is the vapor
density known; we are therefore in want of the direct means of discovering whether in their
molecules there are one, two, or more atoms of the halogens. But their analogies with the
protochloride of mercury, HgCl, and with the protochloride of copper, CuCl, and the specific
heats of the free metals and of their compounds make us assume that in the molecules of each of
these compounds there is one atom of metal and one of halogen. According to this supposition,
the atomic weight of potassium is K = 39, that of sodium Na = 23, that of silver Ag = 108. These
numbers multiplied by the respective specific heats give the same product as the atomic weights
of the substances previously examined:
Name of Substance
Atomic Weight
= p
Specific heats of unit
weight = c
Specific heats of the atoms
= p x c
Solid Bromine
80
0.08432
6.74560
Iodine
127
0.05412
6.87324
Solid Mercury
200
0.03241
6.48200
Copper
63
0.09515
6
Potassium
39
0.169556
6.612684
Sodium
23
0.2934
6.7482
Silver
108
0.05701
6.15708
Besides this, the specific heats of chlorides, bromides, and iodides of these metals confirm
215
the view that their molecules contain the same number of atoms of the two components. Thus:
Formulae and
names of the
compounds
Weights of their
molecules
= p
Specific heats of
unit weight
= c
Specific heats of
the molecules
= p x c
Number of atoms
in the molecules
= n
Specific heat of
each molecule
= p x c/n KCl Chl. of Potassium
74.5
0.17295
12.884775
2
6.442387
NaCl Chl. of Sodium
58.5
0.21401
12.519585
2
6.259792
AgCl Chl. of Silver
143.5
0.09109
13.071415
2
6.535707
KBr Brom. of Pot.
119
0.11321
13.47318
2
6.73659
NaBr Brom. of Sodium
103
0.13842
14.25726
2
7.12863
AgBr Brom. of Silver
188
0.07391
13.89509
2
6.94754
KI Iod. of Potassium
166
0.08191
13.59706
2
6.79853
NaI Iod. of Sodium
150
0.08684
13.0260
2
6.5130
AgI Iodide of Silver
235
0.06159
14.47365
2
7.23682
Are the atoms of potassium, sodium, lithium, and silver equal to ½ molecule, like that of
hydrogen, or equal to a whole molecule, like that of mercury? As the vapor densities of these
elements are wanting, we cannot answer the question directly; I will give you later some reasons
that incline me to believe that the molecules of these elements, like that of hydrogen, are
composed of two atoms.
Gold makes with each of the halogens two compounds. I show that the first chloride is
analogous to calomel, i.e., that it has AuCl as its formula. The atomic weight of gold deduced
from the composition of the protochloride to which this formula is given corresponds to the law
of specific heats, as may be seen from what follows:
196.32 x 0.03244 = 6.3696208 Au Specific heat of Gold
I show in the sequel that the first or only chlorides of the following metals have a
constitution similar to the bichloride of mercury and that of copper; that is, for each atom of
metal they contain two atoms of chlorine.
Not knowing the density in the gaseous state of these lower or only chlorides, we cannot
216
show directly the quantity of chlorine existing in their molecules, yet the specific heats of these
free metals and of their compounds show what I have said above. I write the quantities of these
different elements combined with the weight of two atoms of chloride in the lower or only
chlorides, and confirm in these quantities the properties of the other atoms; I write the formulae
of the lower chlorides, bromides, and iodides all as MCl2, and verify that they correspond to the
laws of specific heats of compound substances.
Names of Substances
Symbols and weights of
the atoms
Specific heats of unit weight
Specific heats of the
atoms
Iodine
I = 127
0.05412
6.87324
Solid Mercury
Hg = 200
0.03241
6.48200
Copper
Cu = 63
0.09515
6
Zinc
Zn = 66
0.09555
6.30630
Lead
Pb = 207
0.0314
6.4993
Iron
Fe = 56
0.11379
6.37224
Manganese
Mn = 55
0.1181
6.4955
Tin
Sn = 117.6
0.05623
6.612648
Platinum
Pt = 197
0.03243
6.38871
Calcium
Ca = 40 14
Magnesium
Mg = 24
Barium
Ba = 137
Formulae
of the
compounds
Weights of their
molecules
= p
Specific heats
of unit weight
= c
Specific heats of
the molecules
= p x c
Number of atoms
in the molecules
= n
Specific heat
of each atom
= p x c / n
HgCl2
271
0.06889
18.66919
3
6.22306
ZnCl2
134
0.13618
18.65666
3
6.21888
SnCl2
188.6
0.10161
19.163646
3
6.387882
MnCl2
126
0.14255
17.96130
3
5.98710
14
[The columns to the right of Ca, Mg and Ba are blank in the original. You recall that calcium and magnesium are
very reactive, both readily oxidizing with minimal heating. Perhaps this complicates finding their specific heat
capacities.]
217
Formulae
of the
compounds
Weights of their
molecules
= p
Specific heats
of unit weight
= c
Specific heats of
the molecules
= p x c
Number of atoms
in the molecules
= n
Specific heat
of each atom
= p x c / n
PbCl2
278
0.06641
18.46198
3
6.15399
MgCl2
95
0.1946
18.4870
3
6.1623
CaCl2
111
0.1642
18.2262
3
6.0754
BaCl2
208
0.08957
18.63056
3
6.21018
HgI2
454
0.04197
19.05438
3
6.35146
PbI2
461
0.04267
19.67087
3
6.55695
Some of the metals indicated above make other compounds with chlorine, bromine, and
iodine, whose molecular weights may be determined and compositions compared; in such cases
the values found for the atomic weights are confirmed. Thus, for example, a molecule of
perchloride of tin weighs 259.6, and contains 117.6 of tin (= Sn) and 142 of chlorine (= Cl4). A
molecule of perchloride of iron weighs 325, and contains 112 of iron (= Fe2) and 213 of chlorine
(= Cl6).
For zinc there are some volatile compounds that confirm the atomic weight fixed by me.
Chemists, believing chloride of zinc to be the same type as hydrochloric acid, made the atom of
zinc Zn = 33, that is, half of that adopted by me; having then prepared some compounds of zinc
with the alcohol radicals, they were astonished that, expressing the composition by formulae
corresponding to gaseous volumes equal to those of other well-known compounds, it was
necessary to express the quantity of zinc contained in the molecule by Zn2. This is a necessary
consequence of the quantity of zinc represented by other chemists by Zn2 being only a single
atom, which is equivalent in its saturation capacity to two atoms of hydrogen. Since in the sequel
of my lectures I return to this argument, you will therefore find it spoken of later in this abstract.
Are the atoms of all these metals equal to their molecules or to a simple sub-multiple of
them? I gave you the above reasons that make me think it probable that the molecules of these
metals are similar to that of mercury; but I warn you now that I do not believe my reasons to be
of such value as to lead to that certainty that their vapor densities would give us, if we only knew
them.
Reviewing what I show in the lecture of which I have given you an abstract, we find it
amounts to the following: Not all the lower chlorides corresponding to the oxide with one atom
of oxygen have the same constitution; some of them contain a single atom of chlorine, others
two, as may be seen in the following list:
HCl - Hydrochloric acid
HgCl2 - Bichloride of Mercury
HgCl - Protochloride of Mercury
CuCl2 - Bichloride of Copper
CuCl - Protochloride of Copper
ZnCl2
- Chloride of Zinc
218
KCl - Chloride of Potassium
PbCl2 - Chloride of Lead
NaCl - Chloride of Sodium
CaCl2
- Chloride of Calcium
LiCl - Chloride of Lithium
SnCl2 - Protochloride of Tin
AgCl - Chloride of Silver
AuCl - Protochloride of Gold
PtCl2 - Protochloride of Platinum
Regnault, having determined the specific heats of the metals and of many of their
compounds, had observed that it was necessary to modify the atomic weights attributed to
them—namely, to divide by 2 those of potassium, sodium, and silver, leaving the others
unaltered; or, vice versa, to multiply these latter by 2, leaving unaltered those of potassium,
sodium, silver, and hydrogen. From this he drew the conclusion that the chlorides of potassium,
sodium, and silver, are analogous to calomel (protochloride of mercury) and to protochloride of
copper; on the other hand, that those of zinc, lead, calcium, etc., are analogous to corrosive
sublimate and to bichloride of copper; but he supposed that the molecules of calomel and of the
analogous chlorides all contained 2 atoms of metal and 2 of chlorine, whilst the molecules of
corrosive sublimate and the other analogous chlorides contained 1 atom of metal and 2 of
chlorine. Here follows the list of the formulae proposed by Regnault.
H2Cl2 - Hydrochloric acid
HgCl2 - Bichloride of Mercury
Hg2Cl2 - Protochloride of Mercury
CuCl2 - Bichloride of Copper
Cu2Cl2
- Protochloride of Copper
ZnCl2 - Chloride of Zinc
K2Cl2 - Chloride of Potassium
PbCl2 - Chloride of Lead
Na2Cl2 - Chloride of Sodium
CaCl2
- Chloride of Calcium
Li2Cl2 - Chloride of Lithium
etc.
Ag2Cl2 - Chloride of Silver
etc.
Au2Cl2 - Protochloride of Gold
In truth, using the data for specific heat alone, it is not possible to decide whether the
molecules of the chlorides written in the first horizontal line are MCl or M2Cl2 ; the only thing
that can be said is that they contain the same number of atoms of metal and of chlorine. But
knowing the densities in the gaseous state of hydrochloric acid and of the two chlorides of
mercury, and thus the weights of their molecules, we can compare their composition and decide
the question; and I have already explained to you how I show to my pupils that the molecules of
the two chlorides of mercury contain the same weight of mercury, and that the molecule of one
of them contains the same quantity of chlorine as hydrochloric acid, i.e., ½ molecule of free
chlorine, whilst the molecule of the other chloride contains twice as much. This shows with
219
certainty that the two formulae Hg2Cl2, HgCl2, are inexact, because they indicate that in the
molecules of the two chlorides there is the same quantity of chlorine and different quantities of
mercury, which is precisely the opposite of what is shown by the vapor densities. The formulae
proposed by me harmonize the results furnished by the specific heats and the gaseous densities.
Now I wish to direct your attention to an inconsistency of Gerhardt. From the theory of
Avogadro, Ampére, and Dumas, that is, from the comparison of the gaseous densities as repre-
senting the molecular weights, Gerhardt drew arguments in support of the view that the atoms of
hydrogen, of chlorine, and of oxygen are half molecules; that the molecule of water contains
twice as much hydrogen as of hydrochloric acid; that in the molecule of ether there is twice as
much of the radical ethyl as in that of alcohol; and that to form one molecule of anhydrous
monobasic acid two molecules of hydrated acid must come together—and yet Gerhardt did not
extend to the whole of chemistry the theory of Ampére, but arbitrarily, in opposition to its
precepts, assumed that the molecules of chloride of potassium, of bichloride of mercury, in fact
of all the chlorides corresponding to the protoxides, had the same atomic constitution as
hydrochloric acid, and that the atoms of all the metals were, like that of hydrogen, a simple sub-
multiple of the molecule.
I have already explained to you the reasons that show the contrary.
After having demonstrated the constitution of the chlorides corresponding to the oxides
containing one atom of oxygen, I postpone the study of the other chlorides to another lecture, and
now define what I mean by “capacity for saturation” of the various metallic radicals.
If we compare the constitution of the two kinds of chlorides, we observe that one atom of
metal is now combined with one atom of chlorine, now with two; I express this by saying that in
the first case the atom of metal is equivalent to 1 of hydrogen, in the second case to 2. Thus, for
example, the atom of mercury, as it is in calomel, is equivalent to 1 of hydrogen, whereas in
corrosive sublimate it is equivalent to 2; the atoms of potassium, sodium, and silver are
equivalent to 1 of hydrogen, the atoms of zinc, lead, magnesium, calcium, etc., to 2. Now it is
seen from the study of all chemical actions that the number of atoms of the various substances
that combine with one and the same quantity of chlorine combine also with one and the same
quantity of oxygen, of sulfur, or of any other substance, and vice versa. Thus, for example, if the
same quantity of chlorine that combines with a single atom of zinc, or lead, or calcium combines
with 2 atoms of hydrogen, of potassium, or of sodium, then the same quantity of oxygen—or of
any other substance that combines with a single atom of the first—will combine with two of the
second. This shows that the property possessed by the first atoms of being equivalent to 2 of the
second depends on some cause inherent either in their own nature or in the state in which they
are placed before combining. We express this constant equivalence by saying that each atom of
the first has a saturation capacity twice that of each of the second. These expressions are not new
to science, and we now only extend them from compounds of the second order to those of the
first order.
For the same reasons given by chemists when they say that phosphoric acid assumes various
saturation capacities without changing in composition, it may also be said that the atom of
mercury and that of copper assume different saturation capacities according as they are found in
the protochlorides or in the bichlorides. Thus, I express the fact that the atoms of these two
metals, being equivalent to 1 atom of hydrogen in the protochlorides, tend, in double
decompositions, to take the place of a single atom of hydrogen, whilst in the bichlorides they
tend to take the place of 2 atoms of hydrogen. For the same reason that we say there are three
220
different modifications of phosphoric acid combined with various bases, we may also say that
there are two different modifications of the same radical mercury or copper. I call the radicals of
the protochlorides and of the corresponding salts, “mercurous” and “cuprous”; those of the
bichlorides and of the corresponding salts are called “mercuric” and “cupric” radicals. To express
the various saturation capacities of the different radicals, I compare them to that of hydrogen or
of the halogens, according as they are electro-positive or electro-negative. An atom of hydrogen
is saturated by one of a halogen, and vice versa. I express this by saying that the first is a
monatomic electro-positive radical and the second a monatomic electro-negative radical: Thus,
potassium, sodium, lithium, silver, and the mercurous and cuprous radicals are monatomic
electro-positive radicals. The biatomic radicals are those that, not being divisible, are equivalent
to 2 of hydrogen or to 2 of chlorine; among the electro-positive radicals there are the metallic
radicals of the mercuric and cupric salts, of the salts of zinc, lead, magnesium, calcium, et cetera,
and amongst the electro-negative we have oxygen, sulfur, selenium, and tellurium, i.e., the
amphidic substances. There are, besides, radicals that are equivalent to three or more atoms of
hydrogen or of chlorine, but I postpone the study of these until later.
Before finishing the lecture I take care to make clear that the law of equivalents must be
considered as a law distinct from the law of atoms.
The latter in fact only says that the quantities of the same element contained in different
molecules must be integral multiples of one and the same quantity, but it does not predict, for
example, that an atom of zinc is equivalent to 2 of hydrogen not only in its compounds with
chlorine, but in all other compounds in which they may replace each other. These constant
relations between the numbers of atoms of various substances that displace one another, whatever
may be the nature and the number of the other components, is a law that restricts the number of
possible combinations, and sums up with greater definiteness all the cases of double
decomposition.
Genoa, 12th March 1858
221
Notes on the Reading
1. With the establishment of the ratios of numbers of atoms in the molecules of compounds, it became
common to specify the number of atoms when naming a compound: e.g., manganese dioxide (MnO2);
sulfur trioxide (SO3); carbon tetrachloride (CCl4); phosphorus pentachloride (PCl5); etc. If the atoms
are present in the compound in 1:1 ratio, then no prefixes are used; e.g., sodium chloride (NaCl).
Several radicals, such as the nitrate radical (NO3), kept their names in compounds; e.g., potassium
nitrate (KNO3). The sulfate (SO4), carbonate (CO3), and phosphate (PO4) radicals are other common
radicals. None of these radicals exist independently; they are always combined with something else;
e.g., sodium carbonate (Na2CO3).
2. The atomic weights established by Cannizzaro’s method are those still in use today (with some
improvements in precision). When you need to select an atomic weight hereafter, read it off the table
in the Appendix to Chapter IX, at the back of the Manual. You should now understand how these
numbers may be determined.
3. Cannizzaro uses the term “double decompositions.” This term will also occur in subsequent readings.
In Experiment 1 you were introduced to the four main classes of chemical reactions:
Simple combination: A + B AB (Why not C?)
Simple decomposition: AB A + B
Single displacement: A + BC B + AC
Double decomposition: AB + CD AD + BC (Also referred to as double displacement)
Exercises with Cannizzaro’s Method
The empirical formula of a compound is one that specifies the correct ratio of atoms in a
molecule of that compound in simple whole number ratios. A molecular formula is one that specifies the
number of atoms of each element in a molecule of the compound; e.g., the empirical formula of hydrogen
peroxide is HO, but the molecular formula is H2O2. (This is the distinction underlying Cannizzaro’s
dispute with Regnault toward the end of the reading.)
In determining the empirical formulas of compounds from weight (or percentage by weight)
determinations, one must take into account the fact that atoms of different elements have different
weights. If 100 g of water is found to contain 11 g of hydrogen and 89 g of oxygen, the formula of water
is not HO8, even though 11 divides 89 eight times. This would be true only if hydrogen and oxygen atoms
had the same weight. To take into account the difference in atomic weights in the computation of an
empirical formula, you might use the following procedure:
Convert the experimental weights (or percentages by weight) into small weight units such that a
hydrogen atom weighs one unit. For convenience, we can call these units atomic weight units (awu). Then
divide by the atomic weights to get the ratio of atoms. Finally, simplify the ratio of atoms to a ratio of
simple whole numbers by dividing by whichever number is smallest. This will yield either a simple whole
number ratio, or a ratio that can be easily converted to a simple whole number ratio. Using the example of
water, we first convert the 11 g of hydrogen to 11 awu of hydrogen and the 89 g of oxygen to 89 awu of
oxygen. Then we divide by the atomic weights to get the ratio of atoms. Since 11 awu ÷ 1 = 11 and 89
awu ÷ 16 = 5.6, the ratio of atoms of hydrogen to atoms of oxygen is 11:5.6. To convert this ratio to
simple whole numbers, divide both sides of the ratio by whatever number is smallest (i.e., 5.6), which
leaves us with a simple whole number ratio of 2:1. Thus, the empirical formula is H2O.
1. In Experiment 1 you mixed 2.6 g of sulfur with 3.5 g of iron and heated it to produce a new
substance. What is the probable empirical formula of the substance formed on heating?
2. It is found that 15.5 g of sodium oxide (Na2O) picks up 4.5 g of water to form a compound, sodium
hydroxide. Write a probable empirical formula for this compound.
222
3. A 5.97 g sample of chloroform on analysis was found to contain 0.60 g of carbon, 0.05 g of hydrogen,
and 5.32 g of chlorine. What is the probable empirical formula?
4. (a) A 0.054 g sample of pure acetic acid was combusted in pure oxygen. The only substances
produced, and their quantities, were carbon dioxide, 0.079 g, and water, 0.032 g. What elements were
present in the acetic acid? What is the most probable empirical formula for acetic acid?
(b) It was found that, when vaporized, 0.52 g of acetic acid occupied 202.0 mL (at 0C and a pressure
of 760 mm of mercury). Given your conclusions in (a), what is the most probable molecular formula
of acetic acid? The density of pure oxygen gas at 0C and 760 mm pressure is 1.429 g/L. (If it were
later found that the volume of the same weight of acid was really 194 mL, how would this change
your molecular formula?)
5. Platinum forms two chlorides, one of which contains 26.7% by weight Cl and the other 42.1% Cl.
What are the empirical formulas for the two substances?
6. Using his molecular formulas, and the electro-chemical theory of Berzelius, Cannizzaro categorizes
the atomic radicals as equivalent to a certain number of hydrogen atoms (if electro-negative) or
chlorine atoms (if electro-positive). The radicals that Cannizzaro mentions explicitly are already
included in the following table. Using the molecular formulas contained in the Cannizzaro reading,
write in the following atomic radicals in the appropriate column: Bromine, Carbon, Nitrogen,
Arsenic, Silicon, Iodine, Boron, Titanium, Aluminum, Phosphorus, Zirconium, Tin.
Electro-Negative Radicals Electro-Positive Radicals
=1H =2H =3H =4H or 4Cl =3Cl =2Cl =1Cl
Hydrogen Magnesium Oxygen Chlorine
Lithium Calcium Sulfur
Sodium Zinc Selenium
Potassium Lead Tellurium
Silver
Copper Copper
Mercury Mercury
223
Dmitri Mendeleev
On the 1860 Congress at Karlsruhe
[The following letter was published in the St. Petersburg Gazette, No. 280 (1860). It was written to
Professor A. A. Voskresenski of the University of St. Petersburg, Mendeleev’s former teacher.]
The chemical Congress just ended in Karlsruhe produced such a remarkable effect on the
history of our science that I consider it a duty, even in a few words, to describe all the sittings of
the Congress and the results that it reached.
The essential reason for calling an international chemical congress was the wish to clarify
and, if possible, agree on the basic difference that exists between the followers of different
chemical schools. At first, Kekulé proposed to settle many questions: the question of the
difference of molecules, atoms, and equivalents; the question of the size of the atomic weights;
i.e., whether the “particle” of Gerhardt or the particle of Berzelius as changed by Liebig and
Poggendorf, and now used by most men, should be accepted; further, the question of formulas;
and finally, reasons for chemical effects. But at the first sitting, September 3rd, the meeting
found it impossible in such a short time to clarify such a great number of questions, and so
resolved to settle only the first two.
There was chosen a commission of thirty members for the preliminary treatment of these
two questions. S. Cannizzaro was finally also on it, whose animated speech, in justice, was met
by general approval. In the second session of the Congress, September 4th, the commission
reported the resolution it had worked out, of this content: It is decided to take a different
understanding of molecules and atoms, considering as a molecule the amount of substance
entering a reaction and determining physical properties, and considering as an atom the smallest
amount of a substance included in a molecule. Further it reached an understanding about
equivalents, considered as empirical, not depending on the understanding about atoms and
molecules. On a vote on this resolution, most raised their hands. Who was against it? Timidly
one hand was raised and then lowered. The result was unexpectedly unanimous and important.
Understanding the difference between atoms and molecules, chemists of all countries understood
the principle of the unitary system. Now when the principle is understood, the consequences will
not admit of great inconsistencies.
The third session, September 5th, was devoted to the questions of atomic weights, chiefly
carbon: whether to accept the new weight of 12 or remain with the former one of 6, until then
used by almost everyone. After a long debate, at its last session, September 6th, J. Dumas made a
brilliant speech proposing to use the new atomic weight only in organic chemistry, leaving the
old one for inorganic. Against this Cannizzaro spoke heatedly, showing that all should use the
same atomic weight. There was no vote on this question, but the great majority took the side of
Cannizzaro.
To this I add the remark that in all the debates there was not one unfriendly word between
both parties. All this, it seems to me, is full guarantee of the rapid success of the new ideas in the
future. Half the chemists have already resolved not to vote against the ideas.
D. Mendeleev, Heidelberg, September 7, 1860
224
225
CHAPTER VIII:
Structural Formulas and Valence
Introduction: Gerhardt’s “System of Types.”
In the essay that will follow this section, Archibald Couper criticizes both Charles
Gerhardt’s “system of types” (also called the “unitary system”) and his method of approaching
the problem of chemical formulas (then called “rational formulas”). To help you to understand
better what Couper is criticizing, the following selections from Gerhardt’s writings are
presented:1
Chemical formulas do not represent, and cannot represent, anything beyond relations and
analogies; the best are those that make evident the greatest number of such relations and
analogies . . . [I]t is their object to indicate in the simplest and most exact manner
possible the relations between various substances and the chemical changes occurring on
their interaction. To represent a substance by rational formula is to embody by means of
conventional signs a number of reactions in which this substance participates.2
We will take acetic acid as an example of the above. Its molecular formula is C2H4O2, as
you may have determined in a problem in the previous chapter. Some important reactions of
acetic acid are listed below:
(i) The acid with some metals, or metallic hydroxides, gives a salt formed by the metal
displacing one-fourth the hydrogen in the acid:
2C2H4O2 + Mg = (C2H3O2)2Mg + H2
C2H4O2 + NaOH = (C2H3O2)Na + H2O
(ii) The action of phosphorous pentachloride on acetic acid results in one atom of chlorine
replacing both an atom of oxygen and an atom of hydrogen (i.e., an hydroxyl group):
5C2H4O2 + PCl5 = 5C2H3OCl + H3PO4 + H2O
(iii) Heating a mixture of the sodium salt and the sodium hydroxide gives sodium carbonate
and the hydrocarbon methane (a gas):
C2H3O2Na + NaOH = Na2CO3 + CH4
(iv) The products of an electrolysis of acetic acid are carbon dioxide, hydrogen, and ethane:
2C2H4O2 = 2CO2 + H2 + C2H6
1 Much of the commentary that follows is taken from Ida Freund, The Study of Chemical Composition: An Account
of its Method and Development (Dover, 1968), pp. 507-511.
2 Charles Gerhardt, Traité de chimie organique, volume 4 (Paris, 1856), pp. 563 et seq.
226
These reactions find their representation in the formulas: (i) C2H3O2H, (ii) C2H3OOH,
(iii) CH4CO2, (iv) CH3CO2H. Gerhardt continues:
Is a rational formula permanently binding, or in other words, can a substance have one
rational formula only? A combination of two or three simple atoms, such as HCl or K2S,
cannot be decomposed in more ways than one, but if the number of atoms in the molecule
is greater, it is evident that the double decompositions that the molecule can undergo can
be various. This is especially true of organic substances.3
August Kekulé, at that time a disciple of Gerhardt, further explained:
The rational formulas are decomposition formulas, and in the present state of the science
they can be nothing else; they aim at giving a representation of the chemical nature of a
substance by a notation that indicates the atomic groups that remain unattacked in a series
of reactions (i.e., the radicals), or by emphasizing the components that, in certain often
recurring changes, play an important part (i.e., types). Any formula that represents certain
changes is rational, but amongst different such formulas, that one is most rational that
simultaneously represents the greatest number of changes . . . The formula showing the
greatest amount of resolution into its component parts will most completely represent the
nature of the substance to which it belongs.4
According to these views any one of the formulas given above for acetic acid has its
legitimacy, but that which represents it by CH3COH is the best, because it is consistent with
the greatest number of reactions—in fact, all four reactions above. The formulas recognize the
presence within the molecule of certain definite compound “residues,” or “radicals”—that is, an
element or a group of elements that during a whole series of chemical reactions remain together.
However, Gerhardt specifies his understanding of radicals by saying that “unlike the majority of
chemists, I look upon radicals in a sense of relation, and not in that of substances which are
isolated or can be isolated.”5
These radicals were found to be endowed with a definite and characteristic substituting
and combining power, which Gerhardt characterized in terms of a “type” or typical substance.
Thus he describes this to be the principal work of the chemist:
To arrange organic compounds in series, that is, to determine the laws according to which
the properties in a given type are modified by substitution of an element or group of
elements for other elements, this is the constant purpose of the chemist philosopher.
These thousands of compounds which he produces in his laboratory are for him,
however, the terms which serve him to construct his series. Today, in the imperfect state
of the science, there is still need for many terms; but later, knowledge of certain series
3 Ibid.
4 Friedrich August Kekulé, Liebig’s Ann. Chem., vol. 6 (1858), p. 129.
5 Gerhardt, Traité de chimie organique, p. 568.
227
will eliminate direct study of many other terms whose properties he will be able to
predict with the same certainty as he predicts today the properties of propionic or valeric
alcohols, even though he has not yet obtained these alcohols.
In the state of the science, organic compounds can be related to three or four
types, each capable of giving series which resemble those represented by formic and
stearic acids, potash, and sulfuric acids.6
Elsewhere Gerhardt gives the following examples:
In order to compare the radicals amongst themselves, I propose to refer them all to the
radical of hydrogen, and consequently I named them monatomic, diatomic, triatomic
according to the quantity of hydrogen that they are capable of replacing in the type H2O;
i.e., according as to whether they are equivalent to 1, 2, or 3 atoms of hydrogen, so for
instance in [ethyl] alcohol and in ether:
C2H5 C2H5
O O
H C2H5
C2H5, the ethyl radical, is monatomic because it replaces H (one atom of hydrogen) in the
type water.
In anhydrous or hydrated sulfuric acid:
SO2
OSO2 O2
H2
SO2, the radical sulfuryl, is diatomic because it replaces H2 (two atoms of hydrogen) in
the type water . . .
But since one and the same substance can be represented by two or more different
rational formulas according to the special double decomposition that it is intended to
indicate, it is evident that a substance can also be formulated in terms of different
radicals. So nitric acid can be depicted by the three formulas:
NO2 NO N
O O2 O3
H H H
in which the radicals NO2, NO, and N have different equivalents. NO2 is the equivalent
for H, NO is the equivalent of H3, and N is the equivalent of H5, because these three
radicals must be replaced by different quantities of hydrogen in order to form water,
thus:7
6 Gerhardt, Ann. Chim. Phys., vol. 37 (1853), p. 285.
7 Gerhardt, Traité, p. 600.
228
H H3 H5
O O2 O3
H H H
Gerhardt further explains his system by saying:
In deriving a body from the water type I intend to express that to this body, considered as
an oxide, there correspond a chloride, a bromide, a sulfide, a nitride, etc., susceptible of
double decompositions, or resulting from double decompositions, analogous to those
presented by hydrochloric acid, hydrobromic acid, sulfuretted hydrogen, ammonia, etc.,
or which give rise to the same compounds. The type is thus the unit of comparison for all
the bodies which, like it, are susceptible of similar changes or result from similar
changes.8
Gerhardt used three other types besides that of water, and related all organic compounds to these
inorganic types: water (H2O), hydrogen (H2), hydrogen chloride (HCl), and ammonia (NH3). He
summarizes the other three types as follows:
The hydrogen type can undergo the same substitutions as the water type and
produce as many combinations.
The compounds resembling marsh gas,9 known as hydrides, are evidently related
to hydrogen as alcohols are to water; the ethyl and methyl radicals correspond to the
ethers of these alcohols. Aldehydes are to hydrogen as monobasic acids are to water;
acetyl, benzoyl, and other oxygenated radicals correspond to acid anhydrides; the
acetones, finally, as Mr. Chancel has already remarked, represent the esters of the
aldehydes and consequently are to hydrogen as the esters of monobasic acids are to
water.
The hydrochloric acid type gives rise, on the one hand, to hydrochloric ethers,
that is, to chlorides resembling chloride of potassium or chlorides of electropositive
elements, when the substitution is effected by hydrocarbon groups; and, on the other
hand, to electronegative chlorides corresponding to monobasic acids, like acetyl chloride
or benzoyl chloride, when the same substitution is effected by groups contained in these
monobasic acids.
Finally, the ammonia type produces alkalis able to combine with acids, or amides
able to combine with bases (oxide of silver, mercury, copper, etc.), according to whether
the substitution on the hydrogens of the ammonia is effected by groups which give rise to
bases (alcohols, organic oxides), or by groups which produce organic acids. The bodies
resembling the hydrate of oxide of ammonia are represented at the other end of the series
8 Gerhadt, Ibid., p. 586.
9 Now referred to as methane (CH4).
229
by acid amides.
It can be seen by this rapid summary how the application of the notion of series
permits simplification of the general theory of organic compounds. They no longer terrify
by their number and variety, for, instead of being formulated by special theories which
lack any connection, as they are called ethers, amides, alkalis, or acids, they become
simply terms whose properties can be predicted according to the place they occupy in the
series. And what certainly adds to the advantage of such a system is the similarity of
method of formation or decomposition which it expresses for all the bodies which it
contains. Experiment shows, in fact, that organic compounds are almost all the result of
double decompositions resembling those which we effect in mineral chemistry.10
Thereby Gerhardt could represent most organic reactions as double decompositions, and “by
exchanging their hydrogens among certain groups, these types give rise to acids, to alcohols, to
ethers, to hydrides, to radicals, to organic chlorides, to acetones, and to alkalis.”11 Unknown
compounds could be predicted in large numbers by this scheme of classification.12
When discussing the subject of formulas, Gerhardt repeatedly says:
It is so prevalent an error to suppose the possibility of representing molecular constitution
by means of chemical formulas, or in other words by the actual arrangement of the atoms,
that I may find it impossible to persuade certain of my readers to the contrary . . .
Chemical formulas are not intended to represent the arrangement of atoms.13
It is fair to assume from his manner of writing that Gerhardt did not even contemplate a
future possibility of such a representation. Couper had this very object for his aim.
* * * * *
10
Gerhardt, Ann. Chim. Phys., vol. 37 (1853), pp. 285-342.
11
Ibid.
12
See Gerhardt’s tables in Traité de chimie organique, pp. 612-613.
13
Gerhardt, Ibid., p. 566.
230
Archibald S. Couper
On A New Chemical Theory1
[Archibald Couper pioneered the idea of deducing structural formulas from the properties
of the elements, but his research did not benefit from the work of Cannizzaro who helped to
determine atomic weights and molecular formulas with greater accuracy. Couper, for example,
treats each oxygen atom as a pair of oxygen atoms because he takes the atomic weight of oxygen
to be 8, rather than 16. Consequently, the number of oxygen atoms in his molecular formulas
should be halved. Similarly, in the first half of his essay he treats each carbon atom as a pair of
carbon atoms because he takes the atomic weight of carbon to be 6, rather than 12. For the sake of
the reader, the corrected molecular formulas have been added to the text in square brackets
immediately following Couper’s molecular formulas.
To simplify his structural formulas, Couper does not draw all of the valence bonds
between individual atoms, but frequently abbreviates. For example, he often draws a single dotted
line from C to H3, although he argues that each hydrogen atom bonds separately to carbon. To aid
the reader, structural formulas with all of the bonds drawn in have been added to the text in
square brackets following Couper’s structural formulas. In some cases this requires drawing
“double bonds” to satisfy the valence requirements. For example, since oxygen always has a
valence of two, we draw two bonds between the carbon and the oxygen atom in the structural
formula of carbon monoxide: C=O. Following the modern convention, the structural formulas in
square brackets use solid lines to represent the chemical bonds that join one atom to another. It is
worth noting that the French version of Couper’s essay uses solid lines rather than the dotted lines
found in the original English version.
In some cases Couper uses outdated chemical symbols: Ka for calcium, Az for nitrogen,
and Ph for phosphorus. The molecular and structural formulas in square brackets use the modern
symbols: Ca for calcium, N for nitrogen, and P for phosphorus.
The passages contained in curly brackets {…} were included in the French version of this
paper, but not in the original English version.]
The end of chemistry is its theory. The guide in chemical research is a theory. It is
therefore of the greatest importance to ascertain whether the theories at present adopted
by chemists are adequate to the explanation of chemical phenomena, or are, at least,
based upon the true principles that ought to regulate scientific research.
Among those which have lately been developed, there is one, on account of its
apparently numerous merits, which particularly claims investigation, and respecting
which we deem that it would not be unprofitable were either new proofs of its scientific
value furnished, or, on the contrary, should considerations be adduced establishing not
only its inadequacy to the explanation, but its ultimate detriment to the progress of
science. I allude to the system of types as advocated by Gerhardt.
This system, striking alike for the breadth of its conception, and the logical and
consequent manner in which it has been developed, has been controverted from the point
of view afforded by theories less far-reaching than the one under consideration, and even
based upon a one-sided and restricted appreciation of certain chemical reactions. The
1 [From Phil. Mag. (4) 16 (1858), pp. 104-116.]
231
consequence is that this opposition has not impaired the favor with which the unitary
system has been received, but has rather tended to display it in a more advantageous
light.
Imposing as this theory is, it is nevertheless all the more necessary to submit it to
a strict investigation; for there is nothing so prejudicial in the search for truth as the blind
spirit of conservation. A rational belief demands the test of a preliminary doubt.
There are two conditions that every sound theory must fulfill:
1. It must be proved to be empirically true.
2. It must be no less philosophically true.
I admit that this theory is for the most part empirically true, that is to say, it is not
contradicted by many of the facts of the science. Evidence that this condition is only
partially fulfilled is to be found:
1. In the circumstance that the peroxides, for instance, do not fit very
satisfactorily into the types.2
2. The principle of double decomposition cannot well be applied to the
conversion of the anhydrous sulphuric acid into the hydrate of that acid by the action of
one equivalent of water, the formulae of these bodies being, according to Gerhardt, in
their free state O·SO2 [SO3] and H2O. Combined, they become simply SH2O4 [H2SO4]
The same remark applies in like manner to carbonic acid. In these instances the
wonted consequence of Gerhardt is missed. The fact of the density of the vapor of these
bodies being the same in the free as in the combined states may have prevented him from
doubling the formulae of these anhydrous acids. The types of this theory being essentially
types of double decomposition, this instance of simple combination diminishes somewhat
the value of the otherwise great logical merit of this system.
Having taken notice of such exceptions, the empirical truth of the theory may be
otherwise admitted.
{It remains to examine whether it fulfills the no less important condition that it is
not found to be in disagreement with philosophical principles.}
The philosophical test demands that a theory be competent to explain the greatest
number of facts in the simplest possible manner.
In applying this test, three aspects of it require to be taken into consideration:
1. As to the extension of the theory.
2. The explanation it affords of the facts.
3. The manner of this explanation.
As to the first: This theory indeed brings every chemical combinate under a
certain comparative point of view with every other. Herein apparently is its merit.
Nevertheless, should our test be applied to its full extent, it will be found that it is fatal to
this system, in other respects so imposing. The comparative point of view that it adopts is
fundamentally false.
As to the second: It does not explain the facts at all; consequently the most
essential point of the test is unfulfilled.
As to the third: This condition of the test is in like manner unfulfilled, from the
fact of the second not being complied with.
2 [Consider hydrogen peroxide (H2O2); could it be thought of as a member of the water type?]
232
Why is it that Gerhardt’s theory so signally fails in these two essential requisites?
Because it is based upon an old but vicious principle that has already retarded science for
centuries. It begins with a generalization, and from this generalization deduces all the
particular instances. But it does not come within the limits of a chemical paper to enter
upon a discussion that is purely metaphysical. Nevertheless, the theory of Gerhardt can
only be combated upon metaphysical grounds, because it is only in overturning a general
principle of research that the theory can be proposed. Gerhardt’s generalization lacks,
moreover, the merit of being represented by a type having a known existence.
,
from which he derives every chemical combinate, being in itself indefinite, cannot of
course be contained or be produced in any definite body. That, however, which may be
demanded of this type is that in itself it should afford at least an instance of that which it
is meant to represent. Now the part “n” of the type represents the notion of indefinite
multiples of
. But not a single instance of a multiple of
has been proved to exist;
much less has it been proved that there exists, or can exist, multiples of this body in an
indefinite series.3 The perfection or imperfection of the type meant to represent the
generalized notion is, however, a matter of comparatively inferior moment. It is the
principle involved in this generalization which is essentially pernicious.
Should the principle that is therein adopted be applied to the common events of
life, it will be found that it is simply absurd. Suppose that someone were to systematize
the formation of letters into words that formed the contents of a book. Were he to begin
by saying that he had discovered a certain word which would serve as a type, and from
which by substitution and double decomposition all the others are to be derived,—that he
by this means not only could form new words, but new books, and books almost ad
infinitum,—that the word also formed an admirable point of comparison with all the
others,—that in all this there were only a few difficulties, but that these might be
ingeniously overcome,—he would state certainly an empirical truth. At the same time,
however, his method would, judged by the light of common sense, be an absurdity. But a
principle which common sense brands with absurdity is philosophically false and a
scientific blunder.
Suppose the book that had formed the basis of this system were a German one,
where all the words were found to be composed at least of two letters, still even in this
language the viewing and systematizing of words as a series of double decompositions
would be no less ridiculous.
The sure and invincible method of arriving at every truth that the mind is capable
of discovering is always one and the same. It is that, namely, of throwing away all
generalization, of going back to first principles, and of letting the mind be guided by
these alone. It is the same in common matters. It is the same in science. To reach the
structure of words we must go back, seek out the undecomposable elements, viz. the
letters, and study carefully their powers and bearing. Having ascertained these, the
composition and structure of every possible word is revealed. It would be well to call to
3 [Consider, for example, how hydrated sulfuric acid and nitric acid are members of the type water on p.
227. For the former n = 2, for the latter (in one formula) n = 3.]
233
recollection the parallelism of chemical research with that of every other search after
truth; for it has been in overlooking this that in chemistry false and vacillating theories
have been advocated and a wrong route so often pursued. In mathematics the starting-
point is not generalizations, but axioms, ultimate principles. In metaphysics Descartes led
the way of progress by analyzing till he thought he could reach some ultimate elements
beyond which it was impossible for him to go, then studying their force and power, and
proceeding synthetically. The recognition of this method wrought the regeneration of
science and philosophy.
On the other hand, look where Gerhardt’s generalization of Williamson’s
generalization4
leads him, and legitimately too—a fact which his logical spirit clearly
discerned. He is led not to explain bodies according to their composition and inherent
properties, but to think it necessary to restrict chemical science to the arrangement of
bodies according to their decomposition, and to deny the possibility of our
comprehending their molecular constitution. Can such a view tend to the advancement of
science? Would it not be only rational, in accepting this veto, to renounce chemical
research altogether?
These reflections naturally lead to the inquiry after another theory more adequate
to satisfy the just demands that can be made upon it. There is one which, as it is still
supported by many distinguished chemists, cannot be passed over altogether unnoticed. It
is that of the theory of certain combinates in organic chemistry5 which are to be viewed
as analogous to, “playing the part of,” inorganic elements. These are denominated
radicals, and are supposed to be contained in all organic chemical products.
In addition to this, and also in connection with it, there is a doctrine describing
many combinates to be copulated, conjugated, by addition.
It is impossible here to enter upon any extensive criticism of this theory. I can
only remark that it is not merely an unprofitable figure of language, but is injurious to
science, inasmuch as it tends to arrest scientific inquiry by adopting the notion that these
quasi elements contain some unknown and ultimate power which it is impossible to
explain. It stifles inquiry at the very point where an explanation is demanded, by putting
the seal of elements, of ultimate powers, on bodies that are known to be anything but this.
Science demands the strict adherence to a principle in direct contradiction to this
view. That first principle, without which research cannot advance a step, dare not be
ignored; namely, that a whole is simply a derivative of its parts. As a consequence of this,
it follows that it is absolutely necessary to scientific unity and research to consider these
bodies as entirely derivative, and as containing no secret ultimate power whatever, and
that the properties which these so-called quasi elements possess are a direct consequence
of the properties of the individual elements of which they are made up.
Nor is the doctrine of bodies being “conjugated by addition” a whit in advance of
that which I have just been considering. This doctrine adopts the simple expedient of
4 [A. W. Williamson first proposed the idea of a “water type” in 1846; Gerhardt developed the notion and
added to it the three other types.]
5 [Organic combinates are those compounds or compound radicals that are produced by living things,
including materials obtained from deposits formed by once-living things, e.g., coal and petroleum. The
great majority of these compounds contain at least carbon and hydrogen.]
234
dividing certain combinates, if possible, into two imaginary parts, of which one or both
are bodies already known. Then it tells us that these two parts are found united in this
body. But how they are united, or what force binds them together, it does not inquire. Is
this explanation arbitrary? Is it instructive? Is it science?
I may now be permitted to submit a few considerations relative to a more rational
theory of chemical combination.
As everything depends upon the method of research employed, it will in the first
place be necessary to find one that may be relied upon. If the method is good and
conscientiously carried out, stable and satisfactory results may be expected. If, on the
contrary, it is vicious, we can only expect a corresponding issue. A satisfactory method
is, however, not difficult to find, nor is it difficult in its application.
The principle that ought to guide all research is in every case the same. It is that of
analyzing till it is impossible to reach more simple elements, and of studying these
elements in all their properties and powers. When all the properties and powers of the
individual elements are known, then it will be possible to know the constitution of the
combinates that their synthesis produces. It is necessary therefore in chemical research, in
order to ascertain the various qualities and functions of the different elements:
1. To consider the whole of chemistry as one.
2. To take into consideration every known combinate, and to study the character,
functions, and properties displayed by each element for itself, in each of these
combinates, in all their different conditions and aspects. It is by a comparison of the
different bodies among themselves that we are able to trace the part that is performed by
each element separately.
3. To trace the general principles common to all the elements, noting the special
properties of each.
This method is essentially different from that where one class of bodies is chosen
as a point for the restriction of our views of the properties of the others—where only the
qualities found in the first are to be measured out to the rest.
I shall now proceed to inquire how its more thorough application tends to the
development of a rational chemical theory.
It has been found that there is one leading feature, one inherent property, common
to all the elements. It has been denominated “chemical affinity.” It is discovered under
two aspects: (1) affinity of kind; (2) affinity of degree.
Affinity of kind is the special affinities manifested among the elements, the one
for the other, &c., as carbon for oxygen, for chlorine, for hydrogen, &c.
Affinity of degree6 is the grades, or also limits of combination, which the
elements display. For instance, C2O2 [CO] and C2O4 [CO2] are the degrees of affinity of
carbon for oxygen.7 C2O2
may be called the first degree, and C2O4 may be termed the
second degree, and, as a higher degree than this is not known for carbon, its ultimate
6 [Compare what Cannizzaro called “capacity for saturation.”]
7 [The molecular formulas C2O2 and C2O4 are the molecular formulas for what modern chemists call carbon
monoxide (CO) and carbon dioxide (CO2), or the early chemists called “carbonic oxide gas” and “carbonic
acid gas” respectively.]
235
affinity or combining limit.8 Affinity of degree in an element may have only one grade. It
may have, however, and generally has, more than one. Here then is an inherent property
common to all elements, by the removal of which the chemical character of an element
will be destroyed, and by virtue of which an element finds its place marked out in a
complex body.
It is such a property that is required to form the base of a system. Nor would its
suitableness for this purpose be affected by the discovery that the elements are
themselves composite bodies, which view the chemist is perhaps not unwarranted to
adopt.9 For in such a case the necessity would doubtless still be found to exist of adopting
the principle of affinity, or something at least equivalent to it, as the basis of the
explanation of chemical combinates.
{At the moment, however, it is impossible to go back to simpler elements. It is
necessary therefore in the meantime to start from the ascertained affinities and properties
amongst the elements in order to arrive at the theory of their combinates.}
In applying this method, I propose at present to consider the single element
carbon. This body is found to have two highly distinguishing characteristics:
1. It combines with equal numbers of hydrogen, chlorine, oxygen, sulfur, &c.
2. It enters into chemical union with itself.
These two properties, in my opinion, explain all that is characteristic of organic
chemistry. This will be rendered apparent as I advance.
This secondary property is, so far as I am aware, here signalized for the first time.
Evidence as to its being a property of carbon may therefore be required.
It will be found in the following: What is the link that binds together bodies
composed of 4, 6, 8, 10, 12, &c., equivalents of carbon, and as many equivalents of
hydrogen, oxygen, &c.? In these you may remove perhaps all the hydrogen or oxygen,
and substitute so many equivalents of chlorine, &c. It is then the carbon that is united to
carbon. Further, that it is not the hydrogen that is the binding element in these combinates
is evident; thus:
Here the whole four of hydrogen are not bound by a mutual affinity; for each
element of hydrogen can be substituted for one of chlorine in regular series, beginning
with the first and ending with the last. The atoms of oxygen are, on the contrary, united in
pairs (which will be more fully developed hereafter), and only for two atoms of oxygen
two of chlorine can be substituted; thus:
8 [What Couper here calls “ultimate affinity or combining limit,” and will later in this paper call
“combining power,” and “combining energy,” is now also commonly called “valence,” or “quantivalence.”
What he will shortly call “free affinities” are now commonly called “open valences.”]
9 [Although we will not pursue the subject at length in this course, Couper asks an interesting question.
Based on what we have seen this semester, is there any evidence that the so-called atoms are composite?
Consider the multiple saturation capacities, or degrees of affinity, of some atoms, and even the problems
with Berzelius’s electro-chemical theory, given Avogadro’s diatomic elemental molecules.]
236
In the same manner with bodies that contain multiples of C2 [C] united to
hydrogen, &c.
Take the inverse of this. If the four atoms of hydrogen were bound together, we
could evidently expect to form such bodies as:
or for bodies like C4H4, C6H6, C8H8, one would naturally expect to find the carbon
substituted for chlorine, and find bodies like
, H6Cl6, H8Cl8, &c.
These bodies are not only unknown, but the whole history of hydrogen might be
investigated and not a single instance be found to favor the opinion that it has any affinity
for itself when in union with another element.
Now, on the other hand, carbon remains chemically united to carbon, while
perhaps 8 equivalents of hydrogen are exchanged for 8 equivalents of chlorine, as in
naphthaline. Analogous to this is the conversion of [ethyl] alcohol,
, and the hydrocarbide C4H6 [C2H6], into C4Cl6 [C2Cl6].
All the countless instances of substitution of chlorine, &c., tend in the same direction.
They prove beyond doubt that carbon enters into chemical union with carbon, and that in
the most stable manner. This affinity, one of the strongest that carbon displays, is perhaps
only inferior to that which it possesses for oxygen.
Another feature in the affinity of carbon is that it combines by degrees of two:
thus, C2O2 [CO] and C2O4 [CO2], C4H4 [C2H4] and C4H6 [C2H6], C6H6 [C3H6] and C6H8
[C3H8], C8H8 [C4H8] and C8H10 [C4H10], &c.; from these last it is especially evident that
two is the combining grade of carbon. It becomes still more apparent when we compare
the bodies C4H4 [C2H4] and C4H5Cl [C2H5Cl], that is
, &c. Many
such proofs might be added, while on the other hand there are no instances contradictory
of this point. Hence the circumstance that it must ever remain impossible to isolate a
combinate of the form C2H3 [CH3] or C4H5 [C2H5], &c.
Carbon having only two grades of combination of two atoms each, a fact which is
easily traced throughout all organic chemistry, this inherent property of the element may
legitimately furnish two grand types for all its combinates:
The first type will be nC2M4 [nCM4].10
10
[As an example of the first type, consider carbon dioxide C2O4 [CO2] where the application of the general
formula becomes 1C2M4 [1CM4] = M4 and the structural formula with all the valence bonds drawn in is
O2=C2=O2 [O=C=O]. Here the combining power of carbon is 4.]
237
The second type will be nC2M4 – mM [nCM4 – mM].11
As examples belonging to the first type, may be mentioned the alcohols of the
aethylic form, their ethers, the fatty acids, &c.
Thus methylic alcohol12
has the form
,
and aethylic alcohol,
.
In these instances it will be observed that for each double atom of carbon the
combining power is (4) four, which is the ultimate limit of combination for carbon in all
bodies yet produced.
In the latter instance it is apparent, inasmuch as if the combining limit of two C2s
[Cs] be each reduced by 3 in hydrogen or oxygen, there still remains a combining power
of one to each of the two C2s [Cs] which each expends in uniting with the other; therefore
, or what is the same thing,
belongs to the type nC2M4 [nCM4].
Again, the inherent properties of the elements may be viewed as dividing bodies
into primary, secondary, tertiary, and so on, combinates.13
These may be termed so many
orders of complicity. Thus C4H6 [C2H6] is a primary combinate, or it belongs to the first
order of complicity; but
is a secondary combinate,14
or
belongs to the second order of complicity. C2O2 [CO] and C2O4 [CO2] are primary, while
C2O4,2OH [HCO3] and C2O4,2OKa [CaCO3] are secondary.
A primary combinate is then nC2 [nC] united to nM4 or to nM4
– mM2 in such a
manner that the combining energy of the complement (nM4, &c.) either potentially or
actually does not extend beyond nC2.
11
[As an example of the second type, consider carbon monoxide C2O2 [CO] where the application of the
general formula becomes 1C2M4 - 1M2 [1CM4 - 1M2] = M2 and the structural formula with all the valence
bonds drawn in is C2=O2 [C=O]. Here the combining power of carbon is 2.]
12
[Now usually contracted as “methanol.” Likewise aethylic alcohol is now contracted as “ethanol.” They
are sometimes referred to, respectively, as wood alcohol and grain alcohol, given how they were often
produced through distillation of wood and grain. “Methyl” and “ethyl” come from combinations of
[methy], “wine,” [aither], “ether,” and ‘ [hyle], “matter,” because they were thought to be
radicals present in wine and ether, respectively.]
13
[Primary and secondary combinates should not be confused with the two “types” of carbon combinates.]
14
[Couper’s C4H6O2 is an instance of a secondary combinate because, as his structural formula indicates,
the combining energy of the complement O is not all expended upon C2 but is extended to H.]
238
A secondary combinate is one in which the combining energy of the complement
is not all expended upon nC2, but is extended further to one or more of the elements.
On the same principle there are tertiary combinates, &c.
These orders of complicity ought in reality to be subdivided. This, however, I do
not think it necessary for the present to enter upon. It will now be understood why an
alcohol belongs to the type nC2M4, and on the same principle why a free aether belongs
to the same type, thus:
while they are at the
same time secondary combinates.
A secondary combinate, that is to say, a body belonging to the second order of
complicity, is, as will be understood from the principle which forms the ground of the
rational theory, a direct consequence of an inherent property of one or more of the
elements which form the complement to the carbon.
In the instance before us it is a certain property of the oxygen that is the cause of
the secondary combinate. This property is the affinity which one atom of oxygen in
combination always exerts towards another atom of oxygen likewise in combination.
This affinity is modified by the electric position of the element to which the
respective atoms of oxygen are bound. From this property results the fact that, in organic
combinates, the atoms of oxygen are always found double.
For instance, the combining limit of oxygen being two, when two molecules of:
are set at liberty, the free affinities of the oxygen instantly produce the union of
these molecules. The cause of the union of two molecules of C2H3 has already been
remarked. In the two cases, the causes of the union of the respective molecules are in so
far different [sic] that the one is the result of a property of the carbon, while the other is a
result of a property of the oxygen.
The view here adopted of the nature of oxygen is, I am convinced, alone in
conformity with the reactions where the properties of this body develop themselves.
The vapor of anhydrous sulfuric acid, for instance, is conducted into anhydrous
aether. The following will then be the reaction:
entering into
communication with
, the two atoms of the
oxygen of the sulfuric acid and the two atoms of the oxygen of the aether (now in
presence of each other) being in different (perhaps different electric) conditions, mutually
loosen their former affinities and reunite themselves to the (electrically?) different atoms
of oxygen of these respective combinates.
The same principle may naturally be expected to display itself with regard to
acids and bases. The oxygen of an acid unites itself to the (electrically?) different oxygen
239
of water. The oxygen of a base on the same principle has an affinity for the electrically
different oxygen of water.
It will be observed:
1. That the oxygen of the water of an acid can only be expelled by that of a base,
and vice versa.
2. It is to be remarked that it is not the metal of a base which exchanges places
with the hydrogen of the hydrate of an acid; for if that were the case, the affinity of the
oxygen of the metal, and also of the acid, would be greater for the oxygen of the water
than the affinity of the hydrogen for that same oxygen. But this is not so. The very
opposite is the truth. If one atom of hydrogen be withdrawn from the hydrate of an acid
or from the hydrate of an oxide, it is universally accompanied by an atom of oxygen. It is
evident, then, that the affinity between the positive and negative atoms of oxygen is less
than that which attaches these atoms to the element with which they form a primary
combinate.
A consequence of this truth is that it is impossible to double the equivalent of
oxygen, if the chemical equivalents are to be understood as not being in direct
contradiction to any chemical truth or essential feature in the properties of an element.
Carbon differs entirely in this respect from oxygen.
There is no reaction found where it is known that C2 [C] is divided into two parts.
It is only consequent therefore to write, with Gerhardt, C2 [C] as simply C, it being then
understood that the equivalent of carbon is (12) twelve.15
This value of the atom will be adopted in the following part of this paper.
Sulfur, selenium, &c., being bodies displaying properties similar, not to carbon,
but to oxygen, it will be necessary to retain the equivalent value that has generally been
assigned to them.
I have now shown how ordinary alcohol, C2H6O2 [C2H6O], common aether, and
the hydrocarbide, C2H6, belong to the type nCM4. The phenomena which necessitate this
view of the constitution of these bodies have a like consequence in regard to the other
alcohols, glycols, acids, and aethers of this series.
Propyle alcohol16
is:
where it will be seen that
the atom of carbon situated between the two others, on account of being chemically
united to these, is reduced to the combining power of two for hydrogen, oxygen, &c. One
combining power is given up to the carbon upon the one side, and a second to the carbon
upon the other.
It will be observed also, that the primary combinates ought in rigor to be
15 [You have here an example of one kind of difficulty that Cannizzaro cleared up. As noted above, Couper
started his paper using a weight of 6 for carbon (cf. Dalton’s weight of 5). As a consequence of this, every
carbon atom in the foregoing was treated as two carbon atoms. From here on, and in his abstract (at the end
of this paper), he uses 12 as the equivalent weight of carbon.] 16
[Now called “isopropyl alcohol.”]
240
themselves enumerated in an inverse order. The type nCM4 becomes then in reality the
type CM4. This enumeration, however, does not appear to possess any great practical
utility, and it is perhaps preferable simply to denote it in an indefinite manner by adding
“n” to the true type CM4.
In a like manner the butyle alcohol is to be viewed as:
, and so on throughout all the series of these
alcohols. The constitution of the aethers will be evident:
represents the mixed butylic-ethylic aether.
Formic acid is represented by the form
; acetic acid in a
like manner:
.
Propionic acid is:
. The constitution of glycol may be
represented as follows:
.
In like manner as to the acids of these glycols, oxalic acid, for instance, may be
represented as:
.
Respecting these acids, it may perhaps be allowable to suggest the possibility of
the molecules having two poles, and that especially the atom of oxygen, situated at one or
perhaps both, and near to two atoms of oxygen bound together, and forming no secondary
combinate, may be in a state presenting great affinity for basic oxygen. Analogy with the
electric poles may perhaps demand the opinion that all the negative oxygen be situated
upon one side of the molecule. It will in that case be preferable to represent the oxalic
acid as:
241
.
Be that as it may, however, the rational method of investigation proves it to be a
law that in acids of the type nCM4 the presence of two atoms bound together so as to
form only a primary part of the same molecule, and situated close to the negative oxygen,
is necessary to the calling forth or production of this negative state.
This is a particular instance, but it moreover shows generally how the electro-
positive or the electro-negative value of the elements mutually modify and condition the
electro-positive or electro-negative value of each other when in combination.
This law is different from the electric hypothesis that chemists have formerly
defended, but which never could be traced throughout a thoroughgoing application of
their views to organic chemistry.
The law here distinctly enounced [sic] coincides exactly with, and is rendered
apparent by, the application of the theory of chemical combination which I support.
But to return. Glycerine is:
, and glyceric acid
.
Glucose has been perhaps too little investigated to afford data sufficient to
determine definitely its formula. Taking, however, mucic and saccharic acids as starting-
points, these bodies may be meanwhile represented as:
the acids
.
242
Glucose
. 17
It will thus be seen that these combinates all belong to the type nCM4. Many
others might be added. For instance, tartaric acid:
.
And the bibasic acid produced from it by the action of heat will be perhaps:
.
It is my intention to consider, in a future communication, the second type, and to
apply my views to the cyanogen combinates, &c.
{In the meantime I shall only add the way in which I regard the constitution of the
principal cyanogen compounds.
Reasons altogether similar to those that make me regard 4 as the limit of the
combining power of carbon lead me to assign 5 as the limit of combination of nitrogen.
The first degree of combination of this element is met with in ammonia [NH3] and equals
3. The second, which is equal to 5, is found, amongst other chemical compounds, in the
chloride and in the oxide of ammonium [NH4Cl and NH3O], as well as in nitric acid
[HNO3].
From this it follows that carbon and nitrogen, combined in such a manner that
both attain the limits of their combining power, will form a body the free affinity of
which will be exerted in fixing one equivalent of hydrogen or of another element.
Thus the formula of hydrocyanic acid will be:
[ ]
Cyanic acid will be:
[
], cyanuric acid:
17
[Couper has the wrong molecular formula for glucose. It is C6H12O6.]
243
.
In this last formula the atoms of carbon and of nitrogen are first linked by 2 units
of affinity and not by 4, as in the first two examples.}
Addendum to On a New Chemical Theory18
(Note presented by Mr. Dumas)
I have the honor to lay before the Academy the principal features of a new
chemical theory that I propose for organic combinates.
I go back to the elements themselves, of which I study the mutual affinities. This
study is, in my opinion, sufficient for the explanation of all chemical combinates, without
it being necessary to revert to unknown principles and to arbitrary generalizations.
I distinguish two species of affinity, namely: (1) affinity of degree, & (2) elective
affinity. By “affinity of degree,” I mean the affinity that one element exerts upon another
with which it combines in several definite proportions. I call “elective affinity” that
which different elements exert with different intensities upon one another. Taking carbon,
for example, I find that it exerts its combining power in two degrees. These degrees are
represented by CO2 [CO] and CO4 [CO2], that is to say, by the oxide of carbon and
carbonic acid, adopting for the equivalents of carbon and oxygen the numbers 12 & 8.
So far as concerns its elective affinities, carbon differs from the other elements
and exhibits, so to speak, a special physiognomy. The features that characterize this
elective affinity of carbon are the following:
(1) It combines with equal numbers of equivalents of hydrogen, of chlorine, of
oxygen, of sulfur, et cetera, which can mutually replace one another so as to satisfy its
combining powers.
(2) It enters into combination with itself.
These two properties suffice, in my opinion, to explain all that is presented as
characteristic by organic chemistry. I believe that the second is pointed out here for the
first time. In my opinion it accounts for the important and still unexplained fact of the
accumulation of molecules of carbon in organic combinates. In these compounds where
2, 3, 4, 5, 6, etc., molecules of carbon are bound together, it is carbon which serves as
link to carbon.
18
[From Comptes Rendus, 46 (1858), 1157-1160.]
244
It is not hydrogen that can bind together the elements of organic bodies. If, like
carbon, it had the power to combine with itself, it would be possible to form the
compounds of H4Cl4, H6Cl6, H8Cl8.
So far as oxygen is concerned, I admit that an atom of this body in combination
exerts a powerful affinity upon a second atom of oxygen that is itself combined with
another element. This affinity is modified by the electrical position of the elements to
which the atoms of oxygen are respectively attached. The following explanation will
make this conception understood.
The highest combining power known for carbon is that of the second degree, that
is to say, 4.
The combining power of oxygen is represented by 2.
All the combinates of carbon can be referred to two types. One of these is
represented by the symbol nCM4, the other by the symbol nCM4 – mM2, where m < n, or
else nCM4 + mM2, where n can become nil.19
As examples of the first type, the alcohols,
the fatty acids, the glycols, etc., may be added.
Methylic and ethylic alcohols will be represented by the formulae:
It will easily be seen that for methylic alcohol the limit of combination of the
carbon is equal to 4, the carbon in it being combined with 3 of hydrogen and with 1 of the
oxygen. This oxygen, of which the combining power is equal to 2, is in turn combined
with another atom of oxygen, itself united to 1 of the hydrogen.
In the case of ordinary alcohol, each of the two atoms of carbon satisfies its
combining power, on the one hand, by uniting with 3 atoms of hydrogen or of hydrogen
and oxygen, and, on the other hand, by uniting with the other atom of carbon. The oxygen
is combined in the same manner as in the preceding example. In these cases it will be
seen that the carbon belongs to the first type, each atom being combined in the second
degree.
In propylic alcohol20
, the combining power of
the atom of carbon that is situated in the middle is reduced to 2 for hydrogen, since it is
combined chemically with each of the two other atoms of carbon.
Formulae analogous to those preceeding express the constitution of the other
alcohols. The constitution of ether is represented by the formula:
.
19
[It seems that there is a misprint here. Where he says “nCM4 – mM2, where m < n” should read “nCM4
– mM2, where m n.” See footnote 11 above for an example of the first type.] 20
[Now called “isopropyl alcohol.”]
245
Formic acid is:
,
acetic acid is:
.
The constitution of glycol is represented by the formula:
,
that of oxalic acid by the formula:
,
or, if it is desired to join the negative oxygen to one of the poles of the molecule, by the
formula:
Be that as it may, however, it can be seen according to this theory that, in the
constitution of organic acids of the first type, the presence of two atoms of oxygen
combined together in such a manner that both are attached directly to the carbon and
situated near the negative oxygen—that is to say, near the oxygen which carries along
with it the oxygen raised to an electro-positive state by its combination with one atom of
a relatively electro-positive element; that the presence, I say, of these atoms of oxygen is
necessary in order that the negative oxygen may find itself in that electrical state which
gives to the body the properties generally described by the name of acids.
This is a particular case of a general law, because it can be seen, according to this
theory, how the electro-positive or electro-negative value of the elements mutually
modifies and conditions the electro-positive or electro-negative value of the other
elements.
This law differs from the electric hypothesis that chemists have hitherto defended,
but which has never been able to receive a complete application to their views on organic
chemistry; that, on the contrary, which I advance, agrees perfectly with the application of
the theory that I propose to [sic] the facts.
There remains nothing for me but to add the manner in which I formulate salicylic
acid and the terchlorophosphate of salicyl that I made known in a communication
submitted to the Academy at its last sitting.
246
Salicylic acid:
Terchlorophosphate of salicyl21:
These formulae suffice, for the moment, to indicate my ideas on the constitution
of bodies.
21
[This is an example of a tertiary combinate.]
247
Questions and Problems
When drawing your own structural formulas in the following problems, you should draw
in all of the valence bonds. Do not hesitate to use “double bonds” to satisfy the valence
requirements. Couper’s valences are in general agreement with those currently assigned:
(usually) 4 for carbon, (always) 2 for oxygen, (always) 1 for hydrogen, 3 and 5 for
nitrogen. Peroxide linkages, O—O linkages, are not very stable and are rarely
encountered. Here the O’s refer to modern atomic weight = 16 for oxygen atoms and not
to Couper’s atomic weight = 8.
The angles between atoms in the diagrams are not considered to be significant: e.g.,
H H
is equivalent to H—O—H or to
H — O O
H
1. Recall the formula of compounds established by Cannizzaro. What is the most
probable value for the valence(s) of each of the following?
Cl, Br, I, Cu, P, K, Na, Ag, Mg, and Ba.
(The latter 5 each have only one known valence).
2. Draw structural formulas for (a) propane (C3H8), (b) hydrogen peroxide (H2O2), (c)
ammonia (NH3), (d) nitric acid (HNO3), and (e) protochloride of phosphorus (PCl3).
3. Do structural formulas explain the rational formulas (i.e., decomposition formulas) of
Gerhardt and Kekulé? Return to the rational formula for acetic acid: CH3COH. Does
the structural formula for acetic acid explain why the molecule tends to decompose into
the radicals indicated by the rational formula? Does it explain why certain molecular
splittings such as CHCO2 H3 do not occur?
4. Are you able to see why some hydrogen is displaced from acetic acid by Mg (as in
Experiment 4) and some hydrogen is not? Which hydrogen(s) do you think is (are)
displaced? Why?
5. Does the element (or radical) with which a given element (or radical) is united in a
compound influence the reactivity of the former, or is the reactivity independent of what
it is attached to? Give an argument in support of your answer.
6. There are four different butyl alcohols, all of which have the same molecular formula:
C4H10O. Those compounds that have the same molecular formula but some differences in
chemical and physical properties (for example, the four butyl alcohols have different
boiling points) are called isomers ( [iso], “same”; [meros], “part”). Can you
draw structural formulas for all four?
248
7. Try to draw all the possible structural formulas for isomers with the molecular
formulas (a) C3H8O (only three have ever been isolated and characterized), (b) C5H12
(only three have ever been isolated and characterized).
8. Draw a structural formula for sodium oxide. Now draw the structural formula of the
substance formed when 1 molecule of water unites with 1 molecule of sodium oxide. Do
you see why the resulting compound is called sodium hydroxide?
9. Write balanced equations for the following reactions you studied earlier in readings or
experiments. Those substances you know to be water insoluble please so indicate by
underlining. Those substances you know to be gases (under ordinary conditions) so
indicate by drawing a horizontal line above them. (Those substances that are listed but
should not be in the equation draw a line through).
(a) The formation of red calx by heating mercury in air
(b) The burning of magnesium metal ribbon in air
(c) The reaction of magnesium metal ribbon with hydrochloric acid
10. Write the equation for the burning of hydrogen as it would be written by (a)
Lavoisier, (b) Dalton, (c) Cannizzaro. What advances in the language of chemistry does
each successive equation represent?
11. Consider the significance of an atomic theory of the agreement between the number
of isomers predicted using Couper’s valences and structural formulas and the number of
isomers actually discovered.
* * * * *
249
CHAPTER IX:
The Periodic Law
Dmitri I. Mendeleev
The Relation Between the Properties and Atomic Weights of the Elements1
When I undertook to write a handbook of chemistry entitled Foundations of
Chemistry, I had to make a decision in favor of some system of elements in order not to
be guided in their classification by accidental or instinctive reasons, but by some exact,
definite principle…Properties, such as the optical and even the electrical or magnetic
ones, cannot serve as a basis for the system naturally, since one and the same body,
according to the state in which it happens to be at the moment, may show enormous
differences in this regard. With respect to this fact, it is sufficient to remember graphite
and diamond, ordinary and red phosphorus.2 The vapor density that enables us to know
the molecular weight of bodies is not only unknown for most of the elements, but it is
subject also to changes that agree completely with the polymeric transformations as they
have been observed for compound bodies.3 Oxygen and sulfur furnish unambiguous
proof for this fact; the relations between nitrogen, phosphorus and arsenic provide
another confirmation, insofar as these similar elements possess the molecular weights N2,
P4, As4 which are unequal to each other with respect to the number of atoms. But there is
no doubt that the polymerization of an element must go hand in hand with the change in a
number of its properties. One cannot be certain whether for any arbitrarily chosen
element, e.g. platinum, another state would become known and that therefore, the place
1 [Adapted from Selected Readings in Natural Science (Univ. of Chicago Press, 1947). Original in D.I.
Mendeleev, Collected Works, Leningrad, 1934 (in Russian). First published in J. Russ. Chem. Soc. 1
(1869), pp. 60-77.]
2 [Diamond, charcoal, and graphite, and also ordinary and red phosphorus, are examples of “allotropes.”
Allotropes are forms of the same element in the same state (solid, liquid, or gas) that exhibit different
properties (e.g., diamond is very hard, transparent, a poor conductor of heat and electricity; charcoal is soft,
black, and a poor conductor; graphite is soft, opaque with a metal-like lustre, and a good conductor of heat
and electricity). Likewise, white phosphorus is spontaneously flammable in air and glows in the dark, while
red and black phosphorus are stable in the air, and black is a good electrical conductor, though it is not a
metal.]
3 [The term “polymer” was coined by Berzelius and used to refer to molecules composed of the same
elements, and in the same ratio, but whose molecular formulas differed, e.g., acetaldehyde (C2H4O) and
butyric acid (C4H8O2). Mendeleev is here extending the term “polymer” to refer to multiple forms of the
molecules of certain elements which, according to modern usage, are called “allotropes.” Sulfur, for
instance, can form molecules of various numbers of sulfur atoms, such as S2, S4, S6, S7, and S8, going even
up to S20. Rings of eight sulfur atoms are most common, however; this is the yellow crystalline powder
usually called “flowers of sulfur.” (This was used in Experiment 1.) We have seen what Mendeleev calls
“polymeric transformations” of oxygen in Cannizzaro’s references to “electrized oxygen,” or ozone.
Cannizzaro refers to such transformations as “allotropic states.”]
250
of a given element in the system would have to be changed according to its physical
properties. However, everybody does understand that in all changes of properties of
elements, something remains unchanged, and that when elements go into compounds this
material something represents the common characteristics of compounds the given
element can form. In this regard only a numerical value is known, and this is the atomic
weight appropriate to the element. The magnitude of the atomic weight, according to the
actual, essential nature of the concept, is a quantity that does not refer to the momentary
state of an element, but belongs to a material part of it, a part that it has in common with
the free element and with all its compounds. The atomic weight does not belong to coal
and to the diamond, but to carbon.…
For this reason I have endeavored to found the system upon the quantity of the
atomic weight. The first attempt I undertook in this direction was the following: I
selected the bodies with the smallest atomic weight and ordered them according to the
magnitude of their atomic weights. Thereby it appeared that there exists a periodicity of
properties, and that, even according to valency, one element follows the other in the order
of an arithmetical sequence.
Li = 7
Be = 9.4
B = 11
C = 12
N = 14
O = 16
F = 19
Na = 23
Mg = 24
Al = 27.4
Si = 28
P = 31
S = 32
Cl = 35.3
K = 39
Ca = 40
____
_____
_____
_____
_____
In the division of elements with an atomic weight greater than 100 we encounter a
completely analogous series.
Ag = 108
Cd = 112
U = 116
Sn = 118
Sb = 122
Te = 128
I = 127
It is seen that Li[thium], Na [sodium], K [potassium], and Ag [silver] show the same
relationship to one another as do N[itrogen], P[hosphorus], V[anadium], and Sb
[antimony], etc. Immediately the idea arose in me whether it was not possible to express
the properties of elements by their atomic weights and whether one could not base a
system upon this…
In the proposed system, the atomic weight of an element serves to determine its
place. Collecting the groups of elements, known up to now, according to their atomic
weight, leads to the conclusion that the method of ordering elements according to their
atomic weight does not contradict the natural similarity existing among the elements but,
on the contrary, points directly toward it…
Thus the group of fluorine possesses elements that combine, preferentially, with a
single atom of hydrogen, the group of oxygen with two, of nitrogen with three, of carbon
with four atoms of hydrogen. Thus, in this respect, the naturalness of the group-
classification, in an arrangement defined according to the numbers expressing the atomic
weight, does not suffer any disturbance but, on the contrary, is suggested in advance…
All comparisons carried out by me in this direction lead me to the conclusion that
251
the magnitude of the atomic weight determines the nature of the elements, just as the
weight of the molecules determines the properties of many reactions of a compound
body. As soon as this assertion is verified in the further application of the proposed
principle to the study of elements, then we shall approach the epoch where we understand
conceptually the essential differences—and the reasons for the similarity—of the
elements.
I state in advance that the law4 proposed by me does not contradict the general
tendency in natural science and that, so far, it has not been proved, although suggestions
of this kind did exist already. From now on, it appears to me, new interest will be
awakened for the determination of atomic weights, for the discovery of new elements and
for the finding of new analogies among the elements….
[Mendeleev concludes by summarizing the principles of what he will later call the “periodic law”
in his 1871 memoir “The Periodic Law of the Chemical Elements.”]
1. The elements, if arranged according to their atomic weights, show a distinct
periodicity of their properties.
2. Elements exhibiting similarities in their chemical behavior have atomic weights
that are approximately equal (as in the case of Pt [platinum], Ir[idium], Os[mium]), or
they possess atomic weights that increase in a uniform manner (as in the case of K
[potassium], Rb [rubidium], Cs [cesium]). The uniformity of such an increase in the
various groups remained hidden to previous observers, since in their calculations they did
not make use of the conclusions drawn by Gerhardt, Regnault, Cannizzaro, and others, by
which conclusions the true magnitude of the atomic weights of the elements was
determined.
3. The arrangement of elements or of groups of elements according to their atomic
weights corresponds to their so-called valencies, as well as, to some extent, to their
distinctive chemical properties, a fact that can be clearly seen from the row: Li[thium],
Be[ryllium], B[oron], C[arbon], N[itrogen], O[xygen], F[luorine], and that also occurs in
the other rows.
4. The bodies most abundantly found in nature possess a small atomic weight; but
all elements of small atomic weight are characterized by their distinct properties and are,
therefore, typical elements. Hydrogen, being the lightest element, is reasonably to be
chosen as the most typical element of all.
5. The magnitude of the atomic weight determines the character of the element,
just as the magnitude of the molecule determines the properties of a compound body; it is
therefore necessary in the study of compounds to direct attention not only towards the
properties and number of the elements as well as to their mutual behavior, but also
towards their atomic weight. Thus, the compounds, e.g., of S[ulfur] and Te[llurium], Cl
[chlorine] and I[odine], and of others, present, in spite of all their resemblance, distinct
differences.
6. The discovery of numerous unknown elements is still to be expected, for
4 [“law”: seems to refer to the principle that “the magnitude of the atomic weight determines the nature of
the elements,” a precursor to the periodic law Mendeleev formulates in 1871.]
252
instance, of elements similar to Al[uminum] and Si[licon] having atomic weights from 65
to 75.
7. The atomic weight of an element will have to be corrected, eventually, when its
analogues become known. Thus, must not the atomic weight of tellurium be 123 to 126,
and not 128?
8. Certain characteristic properties of the elements can be foretold from their
atomic weights.
253
The Periodic Law of the Chemical Elements1
Dmitri Mendeleev
Just as, until the work of Laurent and Gerhardt, the names molecule, atom, and equivalent
were used indiscriminately, so now is the notion of a simple body often confused with the
notion of an element. Yet these notions must be sharply distinguished in order to avoid
perplexity in our thinking about chemistry.
A simple body is something material, metal or non-metal, which is endowed with
physical properties and the capacity for chemical reactions. To the notion of a simple
body corresponds the molecule consisting of one atom (e.g., Hg, Cd, and probably many
other simple bodies) or of many atoms (S2, S6, C2, H2, Cl2, P4, etc.). A simple body can
appear in allotropic2 and polymeric3 forms and is distinguished from compound bodies
only through the fact that its material parts are the same in kind.
By contrast, those material components of simple and compound bodies which
contribute to the physical and chemical behavior of these bodies are termed elements. It is
to the element that the term atom corresponds. Thus carbon is an element, whereas coal,
graphite, and diamond are simple bodies.
The principal task of modern chemistry is to investigate how the composition,
reactions, and properties of simple and compound bodies depend upon the fundamental
properties of the elements contained in them, so as to make it possible to infer, from the
known character of an element, the unknown composition and properties of its
combinations.
Thus if carbon is judged to be polyvalent, this constitutes a fundamental property
of that element and appears in that element’s combinations.
Of those properties of the elements which can be measured exactly, an extensive
body of data is available only for two—namely, atomic weight and the capacity for
appearing in different forms of combination. The latter property has found expression in a
special doctrine of the valence of elements.
1 [English translation by Joseph & Caroline Haggarty of selections from the German translation of
Mendeleev’s original 1871 Russian article: D. Mendelejeff, “Die periodische Gesetzmässigkeit der
chemischen Elemente,” übersetzt aus dem Russichen von Felix Wreden, Liebigs Annalen der Chemie und
Pharmacie, VIII. Supplementband: 133-229, 1871.]
2 [“allotropic forms”: forms of the same element in the same state (solid, liquid, or gas) that exhibit
different properties, e.g., coal, diamond, and graphite.]
3 [“polymeric forms”: The term “polymer” refers to molecules composed of the same elements, and in the
same ratio, but whose molecular formulas differ, e.g., acetaldehyde (C2H4O) and butyric acid (C4H8O2).
Mendeleev is here extending the term “polymer,” or “polymeric forms,” to refer to multiple forms of the
molecules of certain elements, e.g., ordinary oxygen (O2) and electrised oxygen, or ozone (O3). In modern
usage, different forms of the same element are called “allotropes.”]
254
Of the remaining properties of elements which influence the character of a body,
the physical properties (e.g., cohesion, heat capacity, density, index of refraction,
spectroscopic phenomena, etc.) are, at the present time, still too incompletely worked out
to allow for rigorously scientific generalization. In comparison to our knowledge of their
atomic weights and valences, the available data on these properties of the elements is still
inadequate and fragmentary. However—and this is especially because the physical
properties may be measured easily and exactly—many researchers have already pointed
out the dependence of these physical properties upon one another as well as their
dependence upon the atomic weights and, most of all, upon the molecular weights of the
combinations of the atoms. The importance of the elaboration of this part of chemistry for
the progress of the science can easily be judged from the fact that the notions of atom and
molecule have been based principally on the study of physical properties.
Besides the measurable properties just mentioned, the elements also possess a
series of so-called chemical properties which, although they are not yet measurable, are
understood by chemists and contribute to the character of the elements. Thus elements of
one sort do not combine with hydrogen; they possess, according to the accepted
expression, a basic character, i.e., they produce bases when they take on oxygen; and they
unite with chlorine to form salts. Other (acidifiable) elements combine with hydrogen;
with oxygen they produce only acids; with chlorine they produce only chloranhydrides.
Third are the elements which form the bridge from the first group to the second. Fourth
are the elements which possess an acid character in their higher forms of combination,
and a basic one in their lower forms. Because science does not yet provide a way of
measuring these properties, they are counted among the qualitative differences of the
elements. To the same category also belong those properties of the elements which render
their combinations more stable or less so. Thus certain elements can unite with all others
in combinations which are relatively easy to decompose, whereas, in the corresponding
combinations of other elements, these very same decompositions cannot be induced.
Since the chemical properties just mentioned, and other properties similar to
them, do not allow of exact measurement, they can only with difficulty serve to make
chemical knowledge more universal; observations made solely on the basis of these
properties are uncertain. Nonetheless, these properties should not be disregarded
altogether, since many chemical phenomena are explained through them. As is well
known, Berzelius, among others, counted these properties among the principal features of
elements, and the electro-chemical theory was founded upon them.
In fact, in a study of the properties of elements which is supposed to yield
practical conclusions and chemical predictions, the universal properties of the group to
which a given element belongs and the individual properties of that element are equally
deserving of attention; only after a comparative study of this sort and only on the basis of
a property capable of exact measurement do the properties of the elements admit of
universalization. In atomic weight we now possess, and will possess for a long time yet,
just such a property. For our conceptions of atomic weight have attained such unshakable
solidity—particularly in recent times, since the application of the law of Avogadro and
Ampère, and through the efforts of Laurent, Gerhardt, Regnault, Rose, and Cannizzaro—
255
that one may confidently assert that the notion of atomic weight (as the smallest part of
an element which is contained in a molecule of its combinations) will remain unaltered
through all of the changes in the theoretical conceptions of chemists. To be sure, the
name (atomic weight) does presuppose the hypothesis of the atomic structure of bodies.4
Our concern here, however, is not with names, but with a term which is to be employed
with reservation. Only a comparison of the elements arranged according to their atomic
weight will allow us to broaden our chemical knowledge from the standpoint of the
science of mechanics. Thus the most natural and the most promising approach, as it
seems to me, is to investigate the properties of the elements according as they are
dependent on atomic weight. It is in the determination of this dependence that I see one
of the chief tasks of future chemists; for in respect of its theoretical implications, this task
has the same importance as research into relationships among allotropes. In this essay I
will attempt to demonstrate the aforementioned connection between the atomic weights
of the elements and their other properties—particularly their ability to yield determinate
forms of combination.
….By the term periodic law I designate the reciprocal relationships—to be
developed more fully below—between the properties of the elements and their atomic
weights. These reciprocal relationships obtain for all of the elements, and they take the
form of a periodic function.5
I. The Nature of the Periodic Law
It has been observed for quite some time now that some of the elements with high
atomic weight are analogues of elements with significantly lower atomic weights. Thus
Claus pointed out that Os[mium], Ir[idium], and Pt [platinum], with atomic weights of
approximately 195, possess properties similar to those of Ru[thenium], Rh[odium], and
Pd [palladium], which have a significantly smaller atomic weight (approximately 105).
Marignac stressed the analogy which Ta[ntalum] = 182 and W [tungsten] = 184 bear to
Nb [niobium] = 94 and Mo[lybdenum] = 96. To Au [gold] and Hg [mercury] correspond
the lighter analogues Ag [silver] and Cd [cadmium], as well as the still lighter Cu
[copper] and Zn [zinc]. Cesium and barium are analogues of potassium and calcium, and
of more of the same kind. Parallels of this sort prompt the desire to arrange all of the
elements in the order of their atomic weights—and in doing so, one stumbles across a
startling simplicity in their reciprocal relationships. As proof of this, we present an
example comprised all of light elements with atomic weights from 7 to 36, ordered in
arithmetic sequence according to the magnitude of their atomic weights:
Li = 7; Be = 9.4; B = 11; C = 12; N = 14; O = 16; Fl = 19
Na = 23; Mg = 24; Al = 27.3; Si = 28; P = 31; S = 32; Cl = 35.5.
4 It seems to me that, by replacing the name atomic weight with elementary weight, the notion of atoms can
be avoided in a discussion of the elements.
5 [“periodic function”: In algebra, an expression which yields regularly repeating values while its variable
continually increases.]
256
Here one sees that, as the magnitude of the atomic weight changes, the character
of the elements changes in a regular and gradual manner. In fact, it changes periodically,
i.e., in the same way in both series, so that the corresponding members are analogues of
each other: Na [sodium] and Li[thium], Mg [magnesium] and Be[ryllium], C[arbon] and
Si[licon], O[xygen] and S[ulfur], etc. Thus the corresponding members of each series
yield the same forms of combination—they possess, as it is customarily called, the same
valence. Most important of all is the fact that the transitions from one element to the next
exhibit such regularity in their forms of combination, as may be seen by comparing the
combinations which these elements make with hydrogen and oxygen. This regularity
proves that the arrangement of elements here presented constitutes a natural series, in
which no intermediate members are to be expected. Thus it is merely the last four
members which are able to enter into combination with hydrogen, forming
— — — RH4 RH3 RH2 RH
(where R signifies an element). The stability or decomposability of these hydrogen
compounds under the influence of various agents, their acidic character, their capacity to
exchange hydrogen for metals,6 and other properties change gradually and correspond to
the relative position of the elements in their series. Thus HCl is a prominent acid of great
stability; H2S is a weak acid which can be decomposed by heat; in H3P, the acidic
character is completely gone and the decomposability is increased; in H4Si these changes
are clearer still.
Since all of the elements of the second series enter into combination with oxygen,
it is in these combinations that one can best observe the changes in the properties of the
elements taking place in accordance with the changes in the atomic weights. For a
comparison of this sort we adduce the higher anhydrous oxides….The seven elements of
this latter series yield the following salt-forming oxides:
Na2O Mg2O2 Al2O3 Si2O4 P2O5 S2O6 Cl2O7.
(or MgO) (or SiO2) (or SO3)
Thus the seven universally recognized forms of oxidation correspond to the seven
members of the series mentioned. While these forms of oxidation were discovered a long
time ago, their connection with the fundamental properties of the elements remained
nonetheless unnoticed. As is already evident from simply collocating these seven forms,
there corresponds to their sequence a decrease in basic properties and an increase in
acidic properties.
…A special regularity can also be seen in the composition of the hydroxides:
6 [Acids typically corrode metals, liberating hydrogen, as we saw in Experiments 1 and 4.]
257
Na(OH); Mg(OH)2; Al(OH)3; Si(OH)4; PO(OH)3; SO2(OH)2; ClO3(OH).
…When ordered by the magnitude of their atomic weights, the elements reveal a
regular correlation not merely in their forms of combination, but also in other chemical
and physical attributes.
At the beginning of the series appear bodies with a distinctively metallic
character, while the representatives of the non-metals stand at the end. The former have
basic properties while the latter have acidic properties, and the properties of the bodies
standing in the middle form transitions between the two. In Li2O and Na2O, the basic
properties show themselves more distinctly than in BeO and MgO. These properties
appear but feebly in B2O3 and Al2O3, and these combinations already display, in part,
acidic properties. CO2 and SiO2 have an exclusively acidic character, albeit a weak one;
this character emerges with greater intensity in N2O5 and P2O5, as well as in SO3 and
Cl2O7.
To demonstrate the regularity with which the physical properties change in the
series here presented, we adduce the changes in the densities and in the [atomic]
volumes7 of the members of the second series:
Na Mg Al Si P S Cl
Density 0.97 1.75 2.67 2.49 1.84 2.06 1.33
Atomic Volume 24 14 10 11 16 16 27
…Volatility decreases in the initial members of the first series from Na to Si and
then proceeds to increase. The same pattern can be observed in the oxides, among which
the intermediate ones, MgO, Al2O3, and SiO2, are not volatile.
…All of the remaining elements can be arranged in more or less complete series
which fully correspond to the preceding. The silver series, for example:
Atomic Weight
Ag = 108; Cd = 112; In = 113; Sn = 118; Sb = 122; Te = 125?; J = 127
I am content simply to set forth the densities of these metals, since their agreement with
the preceding series in respect of the rest of their properties needs no further explanation.
Density
Ag = 10.5; Cd = 8.6; In = 7.4; Sn = 7.2; Sb = 6.7; Te = 6.2; J = 4.9
As will be demonstrated at greater length, and as can be seen from the attached
tables, all of the elements fall into ordered arrangements of this sort. This fact indicates
7 [“[atomic] volume”: The atomic weight of a substance (weight per atom) divided by its density (weight
per unit volume) gives a figure which will be proportional to the volume per atom. Of course, the atomic
volumes are relative volumes, just as atomic weights are relative weights.]
258
that the properties of the elements are intrinsically dependent upon their atomic weights.
This dependence could have been foreseen by reason of the atomic theory; for the atomic
weight constitutes one of the variable quantities through which the function of atoms is
determined. It was a consideration of this sort that led me to discover the aforementioned
dependence, and that is why I mention it here.
It follows from the foregoing, and from the other ordered arrangements which I
have set forth to date, that the functions by which the dependence of properties upon the
weights of atoms is expressed all show themselves to be periodic functions. The
properties of the elements first change according to the increasing atomic weights; then
they repeat themselves in a new series of elements—a new period—with the same
regularity as in the preceding series. Consequently, the periodic law can be expressed as
follows: the properties of the elements (and also, therefore, the properties of the simple
and compound bodies formed from them) stand in periodic dependence upon their
atomic weights.
Let us now proceed to determine the function by which this dependence is
expressed. For this purpose we must first of all determine the length of a period, or rather,
the number of members which form a period. What pertains to the expression of this
function is obvious in certain cases (e.g., the forms of oxidation). In other cases, we do
not as of yet have at our disposal any way of giving precise expression to the function—
which, nevertheless, retains its periodic character.
The existence and the properties of a period consisting of seven elements,
corresponding to the period Li[thium], Be[ryllium], B[oron], C[arbon], N[itrogen],
O[xygen], F[luorine], are already evident from the foregoing. Let us call this the small
period or small series. If H[ydrogen] is regarded as standing in the first series, Li, etc.
will be in the second series, Na…in the third, and so on.
Not all of the elements so far discovered, however, belong in the small series. A
further point is still more significant by far. Namely, there is a clearly recognizable
difference between the corresponding members of the even and the odd series (excepting
the first two series, as will be seen below), while at the same time, the members of the
even series have a stronger analogy to one other, just as the members of the odd series
have a stronger analogy to one another. An example will demonstrate this well enough:
4th
series: K Ca — Ti V Cr Mn
5th
series: Cu Zn — — As Se Br
6th
series: Rb Sr — Zr Nb Mo —
7th
series: Ag Cd In Sn Sb Te I
The members of the fourth and sixth series bear a greater similarity to each other
than to the members of the fifth or the seventh series. The members of the even series are
not so clearly metalloid as are those of the odd series. The last members of the even series
(in the lower forms of oxidation) resemble the first members of the odd series in many
respects. Thus Cr [chromium] and Mn [manganese] are similar to the elements Cu
259
[copper] and Zn [zinc] in their basic oxides. On the other hand, there are stark differences
between the last members of the odd series (the halogens) and the first members of the
even series which follow them (i.e., the alkaline metals). At the same time, all of the
elements which cannot be placed in the small periods fall between the last members of
the even series and the first members of the odd series when considered according to their
properties and atomic weights. Thus between Cr [chromium] and Mn [manganese], on
the one side, and Cu [copper] and Zn [zinc] on the other, come Fe [iron], Co[balt], and Ni
[nickel], which form the following transitional series:
Cr = 52; Mn = 55; Fe = 56; Co = 59; Ni = 59; Cu = 63; Zn = 65.
Just as Fe [iron], Co[balt], and Ni[ckel] follow the fourth series, so do
Ru[thenium], Rh[odium], and Pd [palladium] come after the sixth series, and Os[mium],
Ir[idium], Pt [platinum] after the tenth. Both of these series (an even series and an odd)
together with the intermediate series of the elements just mentioned form a large period
of seventeen members. Since these intermediate members do not correspond to any of the
seven groups of small periods, they form an independent group—the eighth. The
members of this group,
Fe = 56; Ni = 59; Co = 59
Ru = 104; Rh = 104; Pd = 106
Os = 193?; Ir = 195?; Pt = 197
resemble each other to the same extent as do the corresponding members of the even
series, such as V[anadium], Nb [niobium], Ta[ntalum] or Cr [chromium], Mo[lybdenum],
W [tungsten], and the like.
The following will clarify this resemblance:
1. All of the metals of the eighth group are grey in color and are not easily
fusible.8 The fusibility increases from Fe [iron] to Co[balt] to Ni[ckel]; the same holds in
the series Ru[thenium], Rh[odium], Pd [palladium] or Os[mium], Ir[idium], Pt
[platinum].
2. Even in comparison with the neighboring elements, these metals have low
atomic volumes. For example, consider the following atomic volumes: Cr = 7.6, Mn =
7.0, Fe = 7.2, Co = 7.0, Ni = 7.0, Cu = 7.2, Zn = 9.2. The atomic volume of Mo = 11.2,
while those of Ru[thenium], Rh[odium], and Pd [palladium] approach 9, with Ag = 10.3
and Cd = 13.0. Correspondingly, the volumes of Os[mium], Ir[idium], and Pt [platinum]
are approximately 9.5, whereas the volume of W = 10.1, Au = 10, and Hg = 15. The
smaller volumes, i.e., smaller distances between the atomic centers, confer upon the
metals of the eighth group low fusibility, low chemical energy, and other properties of
this sort.
3. The metals possess, in the highest degree, the capacity for condensing and
8 [“not easily fusible”: not easy to melt.]
260
releasing hydrogen, as has been verified for Ni[ckel], Pd [palladium], Fe [iron] and Pt
[platinum] (Graham, Raoult).
4. Their highest forms of oxidation are bases or acids of low energy which easily
pass into lower oxides of a clearly basic character….
To explain all of the foregoing propositions more fully, I have provided the
following two tables. In the first, the elements together with their atomic weights are
arranged in large periods; in the second they are arranged in groups and series, and in
such a manner that the differences between the even and odd series stand out clearly.
Observations on Table I: For the sake of brevity, the atomic weights in this table have
been given in round numbers; in the majority of cases, one can be sure of the accuracy of
the measurements neither to the tenths place, nor to the ones. A question mark (?) before
the symbol for an element means that, due to insufficient investigations, no precisely
determined place can yet be assigned to the element in the system. A question mark after
the atomic weight means that the available data on the quantity of the atomic weight
admits of doubt—in other words, that it does not seem possible at this point to determine
the element’s equivalent exactly. Some of the atomic weights have been altered in the
table according to the periodic law (see Chapter 5); thus tellurium, in agreement with the
periodic law, is 125?, not 128 as determined by Berzelius and others.9
9 [Nevertheless, the atomic weight of tellurium has since been verified as equaling 127.61.]
261
Observations on Table II: In this table the groups are designated by Roman numerals.
The first seven groups correspond to the seven members of each series; the eighth has
been characterized earlier (see above). Because of their analogous characteristics, Cu
[copper], Ag [silver], and Au [gold] have been included in the eighth group; at the same
time, these elements can be placed in the first group on account of their lower forms of
oxidation. For reasons to be explained further below, the first two series have been
separated from the rest and have been designated as typical.
…Furthermore, we observe in each even series an increase from the first to the
eighth group in the quantity of oxygen which can combine with the element. Within the
eighth group, this capacity decreases as the atomic weight increases (see above) and
reaches its minimum with Cu [copper], Ag [silver], and Au [gold]; then (with Zn [zinc]
and As [arsenic], Cd [cadmium] and In[dium], Hg [mercury] and Tl [thallium]) this
capacity increases again. As is evident from the second table, Cu [copper], Ag [silver],
and Au [gold] consequently enjoy a twofold status, belonging both to the first group and
to the eighth; in the lower forms of combination they correspond to H[ydrogen] and Na
[sodium] (first group). This similarity is especially prominent in Ag [silver]—a point
which requires no further explanation. There is just as little doubt about the similarity
which the suboxides of copper and gold bear to the oxides of silver; comparison of the
properties of CuCl, AgCl, and AuCl is sufficient proof of this.
…In the groups of analogous elements, those of higher atomic weight possess
more clearly marked basic properties, or else form weaker acids….The basic properties
are more prominent in BaO than in CaO, and more prominent in ThO2 than in ZrO2 or
TiO2; HgO divides MgO or BeO from its combinations; Bi2O3 is a more reactive base
262
than Sb2O3 or As2O3, and P2O3 exhibits no basic properties…
In addition, in the members of a given group, with an increase in atomic weight, it
is not only the capacity to be reduced to simple bodies that increases (consider
Te[llurium] and Se[lenium] relative to S[ulfur], I[ndium] relative to Cl [chlorine], Au
[gold] relative to Cu [copper], and the like); the capacity to yield lower forms of
oxidation which quite often enjoy an exceptional stability and aptitude to form
compounds increases as well. Thus Bi[smuth] yields Bi2O5 only with difficulty, and
customarily, the compounds of bismuth correspond to the form Bi2O3 or BiX3. Likewise,
Pb [lead] does not merely yield PbO2, but also the highly stable oxide PbO—a capacity
with which Sn and Si are not endowed to the same degree. Tl [thallium] does not merely
yield Tl2O3, but also Tl2O, which has been observed neither in the case of In[dium] nor in
that of Al[uminum]. In the group Mg [magnesium], Zn [zinc], Cd [cadmium], and Hg
[mercury], one observes that as the atomic weight increases, there is also a clear increase
in volatility, in the basic properties of the oxide RO, in the capacity for being reduced to
metal, and in the capacity for yielding the oxide R2O. Volatility increases with atomic
weight only in this group10 and in its neighbors; by contrast, volatility decreases in the
groups10
at the extremes, as the example of Cl [chlorine], Br[omine], I[ndium] clearly
shows. It is for exactly the reasons mentioned above that the so-called “noble metals”
occupy the place to which they have been assigned in the system—namely, in the middle
of the large periods, among the members with a high atomic weight, where the elements
with greater capacity for being reduced to metal and with lower reactivity belong.
The foregoing clarifies the nature of the periodic law. Every natural law is
scientifically significant only insofar as it makes possible practical conclusions. That is, it
possesses such significance only if it admits of logical inferences which elucidate what
was unexplained and which point toward phenomena not yet known—especially if the
law prompts predictions which can be confirmed by experiment. In such cases, the
usefulness of the law becomes obvious and its correctness can be tested. At the very least,
such a law stimulates the development of new parts of the science. Accordingly, I would
like to consider more closely certain consequences of the periodic law—namely, the
following applications of it:
To the system of elements [in Section II below];
To the determination of the atomic weights of insufficiently researched elements [in
Section III, below];
To the determination of the properties of yet undiscovered elements [in Section IV,
below];
To the correction of the quantity of atomic weights [in Section V, omitted];
And to the completion of our knowledge of the chemical forms of combination [in
Section VI, omitted].
10
[In Mendeleev’s original Russian text, the word for “series” appears here. But this seems to be a slip on
his part, since only “group” and “groups,” respectively, make sense in this context.]
263
Neither here nor further on will I propose hypotheses to explain the nature of the
periodic law.11 First of all, the law is too simple as it currently stands. Secondly, this new
object of research has not been worked out in sufficient detail to allow for the proposal of
a hypothesis. But the most important reason is the third: the periodic law cannot be
harmonized with atomic theory without skewing known facts about the most accurately
determined atomic weights….
II. On the Application of the Periodic Law to the System of Elements
The system of elements possesses a significance that is not merely pedagogical: it
is not simply a way to facilitate the learning of facts of different kinds which are bound
up with each other and systematically arranged. It also has a scientific significance,
insofar as it uncovers new analogies, and thus opens up new paths for the investigation of
the elements. All systems known up to this point may be divided into two sharply distinct
categories.
In the first category are the artificial systems, which base themselves upon a few
particular characteristics of the elements. Of this sort are the systems of arranging the
elements according to their affinity, their electrochemical properties, their physical
properties (the division between metals and non-metals), their reactions to oxygen and
hydrogen, their valences, and the like. Despite their immediately obvious deficiencies,
these systems deserve our attention, since they possess the merit of a certain exactness
and since each of them has contributed in various ways to the gradual development of our
understanding of chemistry.
To the second category belong the natural systems, which arrange the elements
into groups of analogues on account of many purely chemical characteristics of various
kinds. The universally-known results of these systems have won them preference over the
artificial systems, but they too are afflicted with considerable defects:
1. They lack firm principles for arranging the elements, so that elements like Tl
[thallium], or even Ag [silver], Hg [mercury], and the like, have been assigned to
different groups….
2. Some elements remain without analogies: e.g., Au [gold], Al[uminum],
B[oron], F[luorine], Ur[anium], and the like.
3. These systems lack a universal way of expressing the mutual relationships
between the individual groups within them. Even when considered in relation to what is
external to them, in fact, these systems could not be grasped as a single whole; it is for
this reason that they were always fragmentary.
Since the periodic law possesses, in the forms of oxides and in atomic weights,
unchangeable numerical values for arranging the elements, it leads one to group together
elements which are, in fact, very similar, and at the same time, it corresponds to the
11
Nonetheless, I do know that for a complete understanding of something, one must not only possess
observations (as well as experiments) and laws (as well as systems), but must also grasp their significance.
264
principles which led, one after another, to the artificial systems. Consequently, this law
allows us to establish a system which is free from all arbitrariness and as complete as is
possible. The observations made above and those to be made further on bring the
advantages and the properties of this system to light. Here, I wish to linger somewhat
further only on the application of this system to the determination of the positions of
certain elements—those which have occasioned the widest variety of interpretations. But
I must preface this with a few general remarks.
The position of an element R in the system is determined by the series and the
group to which element R belongs. Hence it is determined by X and Y, the neighboring
elements in the same series, as well as by the two elements in its own group with the next
smaller (Rʹ) and the next greater (Rʺ) atomic weights. The properties of R can be
determined from the known properties of X, Y, Rʹ, and Rʺ. Thus we find in the system
the following series:
(n – 2)th
series Xʹ Rʹ Yʹ
nth
series X R Y
(n + 2)th
series Xʺ Rʺ Yʺ
(Rʺ - R is approximately = R - Rʹ = about 45)
So truly and intimately interdependent are the properties of all of the elements that one
can determine the properties of corresponding compounds by establishing the above
proportions and finding the average values. The relationship which R has to X and Y, on
the one hand, and to Rʹ and Rʺ, on the other, I call the element’s atom-analogy. Thus As
[arsenic] and Br[omine], on the one hand, and Sn [tin] and Te[llurium], on the other, are
atom-analogues of Se[lenium], whose atomic weight is the average of theirs:
78 = 75 + 80 + 32 + 125
4
Accordingly, SeH2, considered in respect of its properties, stands in the middle place,
between AsH3 and BrH, on the one hand, and between SH2 and TeH2, on the other. And
so forth. It is only in the series and groups at the extremes that the proportions of the
atom analogies are not entirely applicable, although even here one can observe clear
reciprocal relationships which can, when used with circumspection, also be expressed by
arithmetic (not geometric) proportions. For example,
Xʹ : X = Rʹ : R = Yʹ : Y
or
Xʹ : Rʹ = X : R = Xʺ : Rʺ,
etc.
These reciprocal relations, to which the system founded upon the periodic law directs our
attention, grant us the ability to explain many isolated and disputed findings….
265
III. The Application of the periodic law to the determination
of the atomic weights of insufficiently researched elements
To determine the atomic weight of an element which has only a few degrees of
combination with oxygen and other elements, or which does not yield different kinds of
compounds at all, one also needs, in addition to its known equivalent (in relation to
H[ydrogen], for example), to find either the physical properties of the simple body (heat
capacity), those of its compounds (vapor density and heat capacity), or instances of
allotropy. Since some of these determinations involve practical difficulties, and since our
methods of research are in some cases defective, the atomic weights of many elements
have been established on the basis of attributes that are sometimes very uncertain….
In such cases the periodic law, as a new way of relating chemical properties and
atomic weights, comes to our assistance. By adopting this law, the atomic weight of an
element can be ascertained on the basis of its known equivalent and some of its known
properties. If E, the equivalent of an element—given by that element’s highest oxide
(assuming that the composition of the highest oxide is E2O, and that of the chloride is
ECl)12—is multiplied by 1, 2, 3, 4, 5, 6, 7, what results are the values of that element’s
possible atomic weights. One of these numbers (that is, E x n), which corresponds to a
still-unoccupied position in the system and, at the same time, to the atom-analogy of the
element, expresses that element’s true atomic weight. For, judging by all that we know up
to this point, only a single element fits in a given position in the system, while the
elements’ relationships of atom-analogy are by their nature very simple.
For example, suppose that there is an element yielding a basic oxide which is not
highly reactive, which does not in turn yield a higher oxide, and whose equivalent = 38.13
(One must not forget that this number unavoidably carries with it a certain degree of
error.) The question is, what is its atomic weight, or what is the formula of the oxide? If
one takes R2O as the formula of the oxide, then R = 38 and the element must be placed in
the first group. But this position is already filled by K [potassium] = 39; according to the
atom-analogy, moreover, there should be a readily soluble and reactive base here. If one
proceeds to take RO as the formula, then the atomic weight = 76, which once again does
not fit in the first group, since Zn [zinc] = 65 and Sr [strontium] = 87; all of the places for
elements with low atomic weights in this group have been taken. If one takes R2O3 as the
formula for the oxide, then the atomic weight R = 114 and the element must be placed in
the third group—and here, in fact, there is an unoccupied place, between Cd [cadmium] =
112 and Sn [tin] = 118, for an element with an atomic weight approaching 114. Judging
by the atom-analogy with Al2O3 and Tl2O3, as well as with CdO and SnO2, the oxide of
this element must have weak basic properties. Consequently, such an element would be
12
[In other words, we calculate the equivalent E of an element if we know its ratio to oxygen (by weight) in
its highest oxide and assume that the molecular formula of its highest oxide is E2O.]
13
[If the weight ratio of an element to oxygen in its highest oxide is 75:16, and we assume that the
molecular formula of its highest oxide is E2O, then its equivalent E is equal to 38 (i.e., 75 ÷ 2 = 37.5).]
266
placed in the third group. If one takes RO2 as the formula for the oxide, the atomic weight
= 152. But such an element cannot be accommodated by the fourth group, because its
unoccupied position must be filled by an element which has an atomic weight of 16214
and which (as a transition from PbO2 to SnO2) possesses weakly acidic properties. An
element with an atomic weight of 152 can also be situated in the eighth group, but, as the
transition from Pd [palladium] to Pt [platinum], it must possess properties so prominent
that they cannot escape the notice of the researcher. Consequently, if the element in
question does not possess these properties, it does not correspond to the proposed atomic
weight, nor to the position in the eighth group. And if one takes R2O5 as the formula, then
R = 190, which does not fit in the fifth group, since Ta[ntalum] = 182 and Bi[smuth] =
208; in addition, these two possess acidic properties in the formula R2O5.
The forms of the oxides RO3 and R2O7 correspond to our element no better.
Hence its only possible atomic weight = 114 and the formula of its oxide is R2O3. Indium
is just such an element. Its equivalent, as determined by Winkler, = 37.8. We must
therefore now assume that the atomic weight is 113 and that the composition of the oxide
is In2O3; up to this point, it was assumed that R = 75 and that the formula of the oxide is
InO. Its atom-analogies from the third group are Al[uminum] and Tl [thallium], and from
the seventh series, Cd [cadmium] and Sn [tin].
Let us now compare the probable properties of indium deduced from the atom-
analogues with those actually observed.
Since the atom-analogues Cd and Sn are easily reducible—when in solution, they
can actually be reduced by zinc—indium must also be obtainable in this way. Since Ag
[silver] (seventh series, first group) melts with more difficulty than Cd [cadmium], and
since the same holds for Sb [antimony] in relation to Sn [tin], the atom-analogy Ag
[silver], Cd [cadmium], In[dium], Sn [tin], Sb [antimony] indicates that indium must be
more easily fusible than Cd [cadmium]—and in fact, it melts at 176° [C]. Ag [silver], Cd
[cadmium], and Sn [tin] are a white or greyish-white color; indium has this property as
well. Cd [cadmium] is less dense than Ag [silver], and Sb [antimony] is negligibly less
dense than Sn [tin]; hence indium must have a somewhat lower density than the average
between Cd [cadmium] and Sn [tin]. And this is actually the case. Cd = 8.6, Sn = 7.2,
hence the density of In must be less than 7.9; the measured value is 7.42. Since Cd
[cadmium] and Sn [tin] oxidize when white-hot and do not rust in the air, these properties
must likewise be prominent in In[dium], albeit less strongly than in Cd [cadmium] and Sn
[tin], since Ag [silver] and Sb [antimony] oxidize with even greater difficulty. All of the
points mentioned above agree with the experimental findings. One arrives at the same
conclusions by comparing In[dium] with Al[uminum] and Tl [thallium]. Thus, for
example, the density of Al = 2.67, that of Tl = 11.8, and the average density would be
7.2….
In order to provide yet another example of the method which can be applied to
research into the elements on the basis of the periodic law, I now pass to the
14
[162 is the mean between the atomic weights of lead and tin, in accordance with the rule of thumb
introduced in section II, above.]
267
determination of the properties of elements which are at present still unknown. Without
the periodic law, there was no available way of predicting the properties of unknown
elements; indeed, we could not presume to form a judgment about gaps in the series of
elements. The discovery of new elements was purely a matter of observation, and hence
dependent either upon chance or upon the extraordinary acumen of the researchers. No
specially theoretical interest lay at the bottom of it. It is for this reason that this all-
important region of chemistry—namely, the study of the elements—was trodden by few
chemists. The periodic law has set before us a new path in this direction.
IV. On the application of the periodic law to the determination
of the properties of yet undiscovered elements
The foregoing has already made manifest the opportunity which the periodic law
offers of ascertaining the unknown properties of elements whose atom-analogues are
known. In addition, Tables I and II, in which the periodic relationships of the elements
are expressed, indicate that, at present, several of the elements which one would expect to
find in the series are missing. Hence I would like to describe the properties of some of the
expected elements, so as to lend assistance to a new and perfectly clear proof—albeit one
that will be possible only in the future—of the correctness of the periodic law as set forth
above. At the same time, determining the properties of unknown elements in advance
provides an opportunity for discovering them, since it allows one to predict the reactions
of their compounds.
To avoid introducing into science new names for unknown elements, I will name
them after the next-lowest analogue of the even or odd elements of the same group by
prefixing to it the Sanskrit name of a number (eka, dvi, tri, catur, etc.). Thus the unknown
elements from the first group receive the names eka-cesium (Ec = 175), dvi-cesium (Dc =
220), etc. If, for example, niobium were unknown, it could have been named eka-
vanadium. These names reflect the analogies clearly…
[Mendeleev goes on in this section to predict the properties of three as yet undiscovered
elements which he calls eka-aluminum, eka-boron, and eka-silicon. Subsequently the elements
gallium (1874), scandium (1879), and germanium (1886) were discovered and their properties
shown to be in remarkable agreement with his predictions.
Following (in the left-hand column) is Mendeleev’s discussion of the properties
anticipated for eka-silicon. The subsequently-reported properties of germanium are counted in the
right-hand column.15
]
…The two elements missing from the fifth
series (from the third and fourth groups) must
have properties which are significantly more
distinctive. Their place in this series is
[Germanium (Ge) possesses the following
properties, investigated by Winkler:]
15
[The comparison is given in Ida Freund, The Study of Chemical Composition, 1904, Dover reprint pp.
480-481.]
268
between Zn [zinc] = 65 and As [arsenic] = 75,
and they will be atom-analogues of
Al[uminum] and Si[licon]; hence we shall
name the one eka-aluminum [Ea] and the
other eka-silicon [Es]….These metals must be
easily obtainable by reduction with carbon or
sodium. Their sulfides will be insoluble in
water…EsS2 will probably be soluble in
ammonium sulfide.
The atomic weight of eka-aluminum will be
about Ea = 68, and that of eka-silicon about
Es = 72.
Their densities will be about 6.0 for Ea and
5.5 for Es. Alternatively, since the [atomic]
volumes of Zn [zinc] = 9, As [arsenic] = 14,
and Se [selenium] = 18, those of Ea and Es
will approach 11.5 and 13 respectively. The
same numbers are obtained by comparing, for
Ea, the volumes of Al[uminum], In[dium],
and Tl [thallium], and for Es, those of
Si[licon], Sn [tin], and Pb [lead], since these
elements are the atom-analogues of Ea and Es
respectively. Thus the volume of Si[licon] =
11 and that of Sn [tin] = 16; hence that of Es
= 13….
Eka-silicon will be extracted from EsO2 or
from EsK2F6 by the action of sodium; it will
only decompose steam with great difficulty; it
will hardly react on the acids, but will more
easily attack the alkalies.
It will appear as a dirty gray metal of low
fusibility and will be turned by calcination
into a powdery oxide, EsO2, also of low
fusibility.
The density of the oxide will be about 4.7,
corresponding to the volume, which, judging
by the volumes of SiO2 and SnO2, will be
about 22.
In its external appearance, in its properties, in
[GeS2 is completely precipitated by H2S in
the presence of mineral acids, and like AsS3,
SnS2, etc., it is soluble in ammonium sulfide.]
[Atomic weight of Ge = 72.3.]
[Specific gravity of Ge = 5.469.]
[Ge has been made by the reduction of GeO2
by carbon, and of K2GeF6 by sodium. It does
not decompose water, is not attacked by HCl,
but is easily soluble in aqua regia {mixture of
nitric and hydrochloric acid}. Solution of
KOH has no action, but molten KOH oxidizes
it with incandescence.]
[The element has a metallic lustre, the color is
grayish white. It does not oxidize in air, but
on ignition it forms the oxide GeO2, a dense
white powder that is very refractory.]
[Specific gravity of GeO2 = 4.703]
269
its reactions, and probably also in its
crystalline forms, this oxide will resemble
TiO2. Since the acid properties of both TiO2
and and SnO2 are but feeble, albeit clearly
recognizable, Es will be of the same
character; indeed, it will be more distinctively
acidic than TiO2. The following proportion is
helpful in this and in similar cases: Es : Ti =
Zn : Ca = As : V. According to this
proportion, the basic properties in EsO2 will
be even weaker than in TiO2 and SnO2,
though clearer than in SiO2. Thus one should
expect a hydrate of EsO2 which is soluble in
acids, although such a solution will be . . .
easily decomposable. . . .
In accordance with TiF4, ZrF4, and SnF4, the
fluoride of ekasilicon will, of course, not be
gaseous….Eka-silicon chloride (EsCl4), by
contrast, will be a volatile liquid; boiling at
100°[C] (probably somewhat lower), since
SiCl4 boils at 57°, and SnC14 at 115° . . .
The density of EsCl4 will be about 1.9 (at 0°)
and its volume will be 113, since the volume
of SiC14 = 112, and that of SnC14 = 115 (the
density of TiCl4 = 1.76).
A marked difference between Es and
Ti[tanium] will consist in this, that Es, like
Si[licon] and Sn [tin], will be able to form
volatile metallo-organic compounds, such as
Es(C2H5)4. Ti[tanium], however, since it does
not belong to an odd series in the system, will
not form compounds of this nature.
Judging from the properties of Sn [tin] and
Si[licon], Es(C2H5)4 will boil at 160°, and its
density will be about 0.96. . . .
[The basic properties of the oxide GeO2 are
very feebly marked, the solubility in acids is
slight; though there are indications of the
existence of oxygen-containing salts.]
[Acids do not precipitate the hydrate from
dilute alkaline solutions; but from
concentrated solutions, acids or CO2
precipitate GeO2.]
[The fluoride GeF4 is not gaseous, only
volatile.]
[The chloride GeCl4 is a liquid boiling at
86C.]
[The specific gravity of GeCl4 at 18C is
1.887.]
[Ge(C2H5)4 is easily obtained.]
[Ge(C2H5)4 boils at 160C and its density is a
little below that of water.]
The examples already discussed suffice to manifest the manner in which the
properties of unknown elements may be determined in advance through the application of
the periodic law; hence I will not enter any further into the description of the properties of
the elements which are still missing in the system….
270
In coming to a judgment on the question which forms the object of this treatise,
one stumbles upon a further question: is the number of elements limited or unlimited? A
number of facts—that the system of elements known up to this point is a finite and, so to
speak, closed one; that the very same elements which we know are found in meteorites,
on the sun, and on the stars; and that, at a high atomic weight, acidic properties gradually
fade away, and most of the elements with high atomic weights are found to be heavy
metals which oxidize with difficulty—lead one, when pondering this question, to suppose
that the number of elements accessible to us is very limited, and to think that, if there
should turn out to be some new heavy metals in the Earth’s core, their number and
quantity will also be very limited.
271
Mendeleev’s 1879 Periodic Table
In a letter which accompanied the French edition of the previous paper in 1879,16
Mendeleev made a further revision in the layout of his table to combine the long-period
and short-period styles, as follows (atomic weights shown are those used in the paper,
rounded to whole numbers). Notice the presence of Ga, Gallium, Mendeleev's eka-
aluminum, which had by this time been discovered:
16
Moniteur Scientifique, July 1879; translated in Chemical News, Volume 40, p. 231 (November 14, 1879).
272
Questions and Problems
1. Draw structural formulas for the higher oxides of the seven elements of the second
series:
Na2O, Mg2O2, Al2O3, Si2O4, P2O5, S2O6, Cl2O7
or MgO, or SiO2, or SO3.
Note that when these elements bond with oxygen, their valence is the same as their
group number, that is, Na [sodium]=1, Mg [magnesium]=2, Al[uminum]=3,
Si[licon]=4, P[hosphorus]=5, S[ulfur]=6, Cl [chlorine]=7.
2. Mendeleev’s summary item #3 (on p. 251) is clearly shown in Table II (on p. 261)
where the group number is the same as the valence of the elements in that group when
they combine with oxygen. Most elements, however, exhibit variable valency (e.g.,
carbon may be 2 or 4, and nitrogen may be 3 or 5). Has not Mendeleev merely chosen
from among those valences that an element exhibits that enables him to fit the
element neatly into his table? If so, what do you make of his claim that the periodic
law “allows us to establish a system which is free from all arbitrariness and as
complete as possible”?
3. Are Berzelius’s comments about the electronegativity and electropositivity of some of
the elements consistent with their placement in Table I?
4. Mendeleev writes: “Every natural law is scientifically significant only insofar as it
makes possible practical conclusions. That is, it possesses such significance only if it
admits of logical inferences which elucidate what was unexplained and which point
toward phenomena not yet known—especially if the law prompts predictions which
can be confirmed by experiment. In such cases, the usefulness of the law becomes
obvious and its correctness can be tested.” How is the Periodic Law “scientifically
significant”?
5. Are you able to convert Mendeleev’s two tables to his 1879 periodic table?
* * * * *
273
Reading: The Modern Periodic Table (see the last page of this manual)
Notes on the Modern Periodic Table
1. Compare the modern periodic table with Mendeleev’s 1879 periodic table. Perhaps the most
conspicuous changes are:
a) The presence of the rows beginning with #58 and #90. These are commonly called the
“rare earths,” or the lanthanides and actinides; if these were inserted in their proper places
in the chart, the chart would be about twice as wide as it is drawn. The size of this row,
however, obviously takes away from the symmetry of the table. Nevertheless, their
atomic weights and, even more so, their chemical properties are very similar.
b) The appearance of a whole new group—VIII, first called the “inert gases,” because of
their stability and therefore unreactivity with other elements, and whence the difficulty in
detecting their existence until experimental technique had improved in the last years of
the 19th
century. In 1962 the name of this group was changed to the “noble gases,”
because they were found to be not entirely chemically inert, although they all strongly
resist combination with other elements. Notice how neatly this group fits into
Mendeleev’s chart as a column with 0 valence.
2. Notice that tellurium (Te) is still listed before iodine (I) (as Mendeleev had it). Mendeleev’s
expectation (summary item #7) that the atomic weight of tellurium would be found to be
smaller than that reported in his day was not fulfilled. Can you find other such atomic weight
anomalies in the chart? How do they compare with Mendeleev’s placement of them? What
does this do to the status of the Periodic Law? Can a scientific law admit exceptions such as
these, or is an explanation needed? Should a theory bend to the data or the data to the
theory?1
3. Study one of the “squares” with some care; pick a square for an element with which you have
some acquaintance. Sort out which items in the square you understand on the basis of your
work during both semesters. Which of the items you recognize are (a) intensive
characteristics, (b) extensive characteristics, and (c) other characteristics?
4. What are the “trends” in electronegativity (group trend and period trend) in the modern
periodic table?
5. Although oxidation states (also known as “oxidation numbers”) and valences are not the
same, and it is a common mistake to equate them, the one can be translated into the other.
1 These deviations are now explained in terms of “isotopes” of a given element. Atoms of the same element are now
thought to vary in weight (due the number of neutrons in each, but that’s another story), and the atomic weight given
in the periodic table is now thought of as an average atomic weight of these “isotopes” ( [iso] + [topos],
meaning “same place” in the periodic table). This average weight is constant because there is a natural abundance of
certain isotopes over others of the same element. However, the greater abundance of a heavier isotope can on
average tip the scales. Does this mean that Mendeleev was wrong to say that atomic weight will tell us the “essential
difference” of an element? Compare the notion of isotopes with Dalton’s claim on p. 136 that “the ultimate particles
of all homogeneous bodies are perfectly alike in weight, figure, etc.” Does this alter anything essential to the atomic
theory?
274
One reason they cannot be equated is that oxidation states have a sign (+ or -), when not zero,
whereas valences are without signs and, except in the cases of the noble gases, are never
zero. Another reason is that it is meaningful to speak of the zero oxidation state of an element
(all pure elements have a zero oxidation state; they acquire + or - oxidation states when they
form compounds). But it is not meaningful to speak of a zero valence for an element (with
the few exceptions noted above). Indeed, most elements exhibit a non-zero valence in the
pure elemental state; e.g., in hydrogen gas (H2) the hydrogen atoms each have a valence of
one, though the oxidation state of each is zero. In the table, zero is not listed as an oxidation
state. It is understood that every element also has a zero oxidation state. We can convert the
numbers representing the oxidation states into numbers representing the valences if we
remove the signs. For “(Bold most stable)” we might substitute “(Bold most common)”.
When an element is more electronegative than the one it is combining with, it always
exhibits the valence corresponding to the negative oxidation state listed for it in the chart—
without the minus sign, of course.
Check some of the “valences” listed with those you have specified for elements in
Chapter IX; e.g., carbon, chlorine, nitrogen, and oxygen. You are not expected to understand
how oxidation states are determined, nor what they are, but you are expected to understand
how valences are determined.
7. The heavy step-line separates the metals (left) from the non-metals (right).
8. When naming binary compounds, the element on the chart to the left of and/or lower than the
second element is named first.
9. Because of the “analogies” that the chart represents, if you are able to read the chart, you
now have considerable predictive power at your command. Below you will have the
opportunity to display some of this power of prediction. Keep in mind that, generally, metals
do not combine with each other to form fixed-composition compounds. (Is there such a thing
as a compound without a fixed composition?) They do, however, often form “solutions”
(called alloys) with each other. (Thus, alloys are sometimes called “Bertollides.”) Most
metals will form compounds with most non-metals and most non-metals will form
compounds with most other non-metals (the noble gases being the least inclined to do so).
10. In order to understand the figures in the chart that you do not now understand, it would be
necessary to study the crystalline structure and the electrical and thermal properties of the
elements, and the dimensions and the internal structure of their atoms.
275
Questions and Problems
1. Assume the element cadmium (no. 48) had not yet been discovered but was still a “hole” in
the chart. On the basis of the elements around it, what characteristics (of those you understand)
would you have predicted for it? Compare these with the magnitudes and properties listed. Do
they agree fairly well?
2. Lavoisier, in the table facing page 185 of the Elements of Chemistry, and elsewhere, indicated
that highly oxidized metals would be acids. Berzelius writes of “the acids of manganese.” Is this
consistent with acidic character as reported in the chart?
3. Which would you predict would be the stronger acid in each of the following pairs: HNO2 or
HNO3? HClO3 or HClO4? H2SO4 or H2TeO4? Why?
4. For the following, state whether or not they would form a compound. (All, of course, can be
merely mixed.) If they would, write (a) a balanced equation for the reaction and (b) the name of
each substance formed underneath its formula. If more than one compound might be formed, list
the one you would expect to be the most common one.
(1) Boron (no. 5) and oxygen
(2) Tin (no. 50) and chlorine
(3) Calcium (no. 20) and sulfur
(4) Hydrogen and selenium (no. 34)
(5) Chromium (no. 24) and oxygen
(6) Sodium (no. 11) and zinc (no. 30)
5. What is the (a) name and (b) structural formula of each of the following:
(1) The substance formed when selenium is burned in oxygen.
(2) The substance formed when the product of the above reaction is reacted with water to
form an acid (they react in a 1:1 molecular ratio).
(3) The substance formed when barium is burned in oxygen.
(4) The substance formed when the product of (3) is reacted with water (again, the
materials react in a 1:1 ratio).
6. Take a few of the specific heat capacities listed (including some near the beginning of the
table). How valid do you consider the law of Dulong and Petit?
276
Philosophical Questions regarding the Atomic Theory
1. According to Mendeleev, “[t]he principal task of modern chemistry is to investigate how the
composition, reactions, and properties of simple and compound bodies depend upon the
fundamental properties of the elements contained in them, so as to make it possible to infer,
from the known character of an element, the unknown composition and properties of its
combinations.” (p. 253) To what extent is modern chemistry, as described by Mendeleev, the
same as, or compatible with, the science of generation and corruption that Aristotle and St.
Thomas describe in the opening pages of this manual (see pp. 6-30)?
2. Define chemical element. Keep in mind the distinction that Mendeleev makes between an
element and a simple body. Are the entries in the periodic table elements according to the
definition of Aristotle and St. Thomas?
3. Couper raises the question of whether the elements themselves are composite bodies (see p.
235). What reasons do we have for thinking that the elements may be composite? If the
chemical elements are composite bodies, does that undermine chemistry as a science?
4. Aristotle and St. Thomas argue that elements are present virtually, or potentially, in a
compound substance. Do any of the properties of the elements we have studied this year fit
with the idea of the elements being virtually present in a compound substance (e.g.,
electronegativity, valence)?
5. Do you understand “the means that nature uses to restrict compounds to the ratios in which
we find them combined” (Proust, p. 129)?
6. Do structural formulas force us to say, as Couper does, that a molecule is a whole that is
simply a derivative of its parts (p. 233)?
7. Is the atomic theory true? If so, why? If not, why not? In contemplating this question, you
might consider the following quotes from chemists and scientists writing toward the end of
the 19th
century.
a) William Whewell, who coined the terms “anode” and “cathode,” in 18402:
We have already seen that the combinations that result from chemical affinity are
definite, a certain quantity of one ingredient uniting, not with an uncertain, but with a
certain quantity of another ingredient. But it was found, in addition to this principle,
that one ingredient would often unite with another in different proportions, and that,
in such cases, these proportions are multiples of one another. In the three salts formed
2 [Excerpt from Chapter 5 of The Philosophy of the Inductive Sciences, founded upon their History, 2 vols. (London,
1840).]
277
by potassa [potassium hydroxide] with oxalic acid, the quantities of each acid that
combine with the same quantity of alkali are exactly in the proportion of the numbers
1, 2, and 4. And the same rule of the existence of multiple proportions is found to
obtain in other cases.
It is obvious that such results will be accounted for if we suppose the base and the
acid to consist each of definite equal particles, and that the formation of the salts
above mentioned consists in the combination of one particle of the base with one
particle of acid, with two particles of acid, and with four particles of acid,
respectively. But further, as we have already stated, chemical affinity is not only
definite, but reciprocal. The proportions of potassa and soda [sodium hydroxide] that
form neutral salts are 590 and 391 in one case, and therefore in all. These numbers
represent the proportions of weight in which the two bases, potassa and soda, enter
into analogous combinations; 590 of potassa is equivalent to 391 of soda. These facts
with regard to combination are still expressed by the above supposition of equal
particles, assuming that the weights of a particle of potassa and of soda are in the
proportion of 590 and 391.
But we pursue our analysis further. We find that potassa is a compound of a
metallic base, potassium, and of oxygen, in the proportion of 490 to 100; we suppose,
then, that the particle of potassa consists of a particle of potassium and a particle of
oxygen, and these latter particles, since we see no present need to suppose them
divided, potassium and oxygen being simple bodies, we may call atoms, and assume
to be indivisible. And by supposing all simple bodies to consist of such atoms, and
compounds to be formed by the union of two, or three, or more of such atoms, we
explain the occurrence of definite and multiple proportions, and we construct the
Atomic Theory.
So far as the assumption of such atoms as we have spoken of serves to express
those laws of chemical composition that we have referred to, it is a clear and useful
generalization. But if the Atomic Theory be put forward (and its author, Mr. Dalton,
appears to have put it forward with such an intention) as asserting that chemical
elements are really composed of atoms, that is, of such particles not further divisible,
we cannot avoid remarking that for such a conclusion chemical research has not
afforded, nor can afford, any satisfactory evidence whatever. The smallest observable
quantities of ingredients, as well as the largest, combine according to the laws of
proportions and equivalence that have been cited above. How are we to deduce from
such facts any inference with regard to the existence of certain smallest possible
particles? The Theory, when dogmatically taught as a physical truth, asserts that all
observable quantities of elements are composed of proportional numbers of particles
which can not further be subdivided; but all that observation teaches us is that if there
be such particles, they are smaller than the smallest observable quantities. In chemical
experiment, at least, there is not the slightest positive evidence for the existence of
such atoms. The assumption of indivisible particles, smaller than the smallest
observable, which combine, particle with particle, will explain the phenomena; but
the assumption of particles bearing this proportion, but not possessing the property of
indivisibility, will explain the phenomena at least equally well.
278
b) Auguste Kekulé, one of those who advanced the notion of valence, in 1867:
The question of whether or not atoms exist is of relatively little significance as far as
chemistry is concerned; that issue belongs more in the realm of metaphysics. In
chemistry, all that is relevant is to decide if the hypothesis of atoms is helpful in
explaining chemical phenomena….I can unhesitatingly state that, from a
philosophical point of view, I do not believe in the actual existence of atoms,
inasmuch as this term is to be understood in the literal sense of indivisible particles of
matter. . . As a chemist, however, I consider the hypothesis of atoms not only useful
but absolutely essential. I would even go a step further and declare my conviction that
chemical atoms exist, with the stipulation that the term designate material particles
that no longer undergo any division in chemical transformations.3
c) Michael Faraday, one of the founders of electromagnetism (and whose work you will
study in detail in Senior Natural Science), in 1865:
I believe that, in the pursuit of physical science, the imagination should be taught to
present the subject investigated in all possible and even in impossible views; to search
for analogies of likeness and (if I may say so) of opposition—inverse or contrasted
analogies; to present the fundamental idea in every form, proportion, and condition;
to clothe it with suppositions and probabilities—that all cases may pass in review, and
be touched, if needful, by the Ithuriel spear of experiment. But all this must be under
government . . . [A]bove all things, let us not cease to be aware of the temptation they
[our hypotheses] offer; or, because they gradually become familiar to us, accept them
as established. We could not reason about electricity without thinking of it as a fluid,
or a vibration, or some other existent state or form. We should give up half our
advantage in the consideration of heat if we refused to consider it as a principle, or a
state of motion. We should scarcely touch such subjects by experiment, and we
should make no progress in the practical application, without hypothesis; still it is
absolutely necessary that we should learn to doubt the conditions we assume, and
acknowledge we are uncertain, whether heat and electricity are vibrations, or
substances, or either….
[I]ndeed, what notion can we form of the nucleus [of an atom surrounded by a
heat atmosphere] independent of its powers? All our perception and knowledge of the
atom, and even our fancy, is limited to ideas of its powers; what thought remains on
which to hang the imagination of an a independent of the acknowledged forces? . . .
Why then assume the existence of that of which we are ignorant, which we cannot
conceive, and for which there is no philosophical necessity?4
3 Quoted in Bernard Pullman, The Atom in the History of Human Thought (Oxford: Oxford University Press, 1998),
231-232.
4 Faraday, Experimental Researches in Chemistry and Physics, vol. 1 (Dover, 1965), p. 480, and vol. 2, p. 290
(italics in original).
279
Appendix to Chapter IX: Relative Atomic Weights (1962)
Element
Symbol
At. #
At. Wt.
Element
Symbol
At. #
At. Wt.
Actinium
Ac
89
(227)
Einsteinium *
Es
99
(254)
Aluminum
Al
13
26.9815
Erbium
Er
68
167.26
Americium*
Am
95
(243)
Europium
Eu
63
151.96
Antimony
Sb
51
121.75
Fermium*
Fm
100
(253)
Argon
Ar
18
39.948
Fluorine
F
9
18.9984
Arsenic
As
33
74.922
Francium
Fr
87
(223)
Astatine
At
85
(210)
Gadolinium
Gd
64
157.25
Barium
Ba
56
137.34
Gallium
Ga
31
69.72
Berkelium*
Bk
97
(247)
Germanium
Ge
32
72.59
Beryllium
Be
4
9.0122
Gold
Au
79
196.967
Bismuth
Bi
83
208.980
Hafnium
Hf
72
178.49
Boron
B
5
10.811
Helium
He
2
4.0026
Bromine
Br
35
79.909
Holium
Ho
67
164.930
Cadmium
Cd
48
112.40
Hydrogen
H
1
1.00797
Calcium
Ca
20
40.08
Indium
In
49
114.82
Californium*
Cf
98
(251)
Iodine
I
53
126.9044
Carbon
C
6
12.01115
Iridium
Ir
77
192.2
Cerium
Ce
58
140.12
Iron
Fe
26
55.847
Cesium
Cs
55
132.905
Krypton
Kr
36
83.80
Chlorine
Cl
17
35.453
Lanthanum
La
57
138.91
Chromium
Cr
24
51.996
Lead
Pb
82
207.19
Cobalt
Co
27
58.9332
Lithium
Li
3
6.939
Copper
Cu
29
63.54
Lutetium
Lu
71
174.97
Curium*
Cm
96
(247)
Magnesium
Mg
12
24.312
Dysprosium
Dy
66
162.50
Manganese
Mn
25
54.9380
280
Element Symbol At. # At. Wt. Element Symbol At. # At. Wt.
Mendelevium*
Md
101
(256)
Ruthenium
Ru
44
101.07
Mercury
Hg
80
200.59
Samarium
Sm
62
150.35
Molybdenum
Mo
42
95.94
Scandium
Sc
21
44.956
Neodymium
Nd
60
144.24
Selenium
Se
34
78.96
Neon
Ne
10
20.183
Silicon
Si
14
28.086
Neptunium*
Np
93
(237)
Silver
Ag
47
107.870
Nickel
Ni
28
58.71
Sodium
Na
11
22.9898
Niobium
Nb
41
92.906
Strontium
Sr
38
87.62
Nitrogen
N
7
14.0067
Sulfur
S
16
32.064
Nobelium*
No
102
(254)
Tantulum
Ta
73
180.948
Osmium
Os
76
190.2
Technetium*
Tc
43
(99)
Oxygen
O
8
15.9994
Tellurium
Te
52
127.60
Palladium
Pd
46
106.4
Terbium
Tb
65
158.924
Phosphorus
P
15
30.9738
Thallium
Ti
81
204.37
Platinum
Pt
78
195.09
Thorium
Th
90
232.038
Plutonium*
Pu
94
(242)
Thulium
Tm
69
168.934
Polonium
Po
84
(210)
Tin
Sn
50
118.69
Potassium
K
19
39.102
Titanium
Ti
22
47.90
Praseodymium
Pr
59
140.907
Tungsten
W
74
183.85
Promethium*
Pm
61
(145)
Uranium
U
92
238.03
Protractinium
Pa
91
(231)
Vanadium
V
23
50.942
Radium
Ra
88
(226)
Xenon
Xe
54
131.30
Radon
Rn
86
(222)
Ytterbium
Yb
70
173.04
Rhenium
Re
75
186.2
Yttrium
Y
39
88.905
Rhodium
Rh
45
102.905
Zinc
Zn
30
65.37
Rubidium
Rb
37
85.47
Zirconium
Zr
40
91.22
* These elements have not been found to occur naturally on Earth.
281
AFTERWORD:
Is the Atom Really an Atom (Indivisible)?
Joseph John Thomson
Selections from
“Carriers of Negative Electricity”1
Introductory
In this lecture I wish to give an account of some investigations which have led to the conclusion
that the carriers of negative electricity are bodies, which I have called corpuscles,2 having a mass
very much smaller than that of the atom of any known element, and are of the same character
from whatever source the negative electricity may be derived.
The first place in which corpuscles were detected was a highly exhausted tube through
which an electric discharge was passing. When an electric discharge is sent through a highly
exhausted tube, the sides of the tube glow with a vivid green phosphorescence. That this is due to
something proceeding in straight lines from the cathode—the electrode where the negative
electricity enters the tube—can be shown in the following way (the experiment is one made
many years ago by Sir William Crookes): A Maltese cross made of thin mica is placed between
the cathode and the walls of the tube.3 When the discharge is past, the green phosphorescence no
longer extends all over the end of the tube, as it did when the cross was absent. There is now a
well-defined cross in the phosphorescence at the end of the tube; the mica cross has thrown a
shadow and the shape of the shadow proves that the phosphorescence is due to something
traveling from the cathode in straight lines, which is stopped by a thin plate of mica. The green
phosphorescence is caused by cathode rays4 and at one time there was a keen controversy as to
1 [Nobel Lecture, December 11, 1906; in Nobel Lectures: Physics, 1901-1921 (Amsterdam: Elsevier, 1967), pp.
145-153; all footnotes have been added by the editor.]
2 [In 1894 G. J. Stoney proposed calling these carriers of negative electricity “atoms of electricity,” or “electrons.”
The latter name was formally adopted a few years after Thomson wrote the above essay.]
3 [A Maltese cross has arms of equal length and is flared at the ends. The advantage of employing this shape in the
present experiment is that it is simple enough to fashion, yet complex enough to throw quite distinctive shadows.
Mica is an aluminum silicate mineral readily split into thin transparent sheets.]
4 [These rays were known for much of the 19
th century. They were called “cathode” rays because they were emitted
from the cathode of the vacuum tube. Even though one rarely hears of cathode rays anymore, the term cathode ray
tube (CRT) is not obsolete. CRTs are specialized and sophisticated versions of vacuum tubes that are still used for
video display in television sets, computer monitors, and other devices. CRTs shoot electrons at a screen coated with
282
the nature of these rays. Two views were prevalent: One, which was chiefly supported by
English physicists, was that the rays are negatively electrified bodies shot off from the cathode
with great velocity; the other view, which was held by the great majority of German physicists,
was that the rays are some kind of ethereal vibration or waves.
The arguments in favor of the rays being negatively charged particles are primarily that
they are deflected by a magnet in just the same way as moving, negatively electrified particles.
We know that such particles, when a magnet is placed near them, are acted upon by a force
whose direction is at right angles to the magnetic force, and also at right angles to the direction in
which the particles are moving.
Thus, if the particles are moving horizontally from east to west, and the magnetic force is
horizontal from north to south, the force acting on the negatively electrified particles will be
vertical and downwards.
When the magnet is placed so that the magnetic force is along the direction in which the
particle is moving, the latter will not be affected by the magnet.
The next step in the proof that cathode rays are negatively charged particles was to show
that when they are caught in a metal vessel they give up to it a charge of negative electricity.
This was first done by Perrin. This experiment was made conclusive by placing the catching
vessel out of the path of the rays, and bending them into it by means of a magnet, when the
vessel became negatively charged.
Electric deflection of the rays
If the rays are charged with negative electricity they ought to be deflected by an
electrified body as well as by a magnet. In the earlier experiments made on this point no such
deflection was observed. The reason of this has been shown to be that when cathode rays pass
through a gas they make it a conductor of electricity, so that if there is any appreciable quantity
of gas in the vessel through which the rays are passing, this gas will become a conductor of
electricity and the rays will be surrounded by a conductor which will screen them from the effect
of electric force, just as the metal covering of an electroscope screens off all external electric
effects.
By exhausting the vacuum tube until there was only an exceedingly small quantity of air
left in to be made a conductor, I was able to get rid of this effect and to obtain the electric
deflection of the cathode rays. This deflection had a direction which indicated a negative charge
on the rays.
Thus, cathode rays are deflected by both magnetic and electric forces, just as negatively
electrified particles would be.
Hertz showed, however, that cathode particles possess another property which seemed
inconsistent with the idea that they are particles of matter, for he found that they were able to
penetrate very thin sheets of metal, e.g. pieces of gold leaf, and produce appreciable luminosity
on glass behind them. The idea of particles as large as the molecules of a gas passing through a
solid plate was a somewhat startling one, and this led me to investigate more closely the nature
of the particles which form the cathode rays.
phosphors, which glow when they are struck by the electron beam. (Thomson's tube glowed green because of the
kind of glass it was made of; other materials glow other colors when struck by electrons.)]
283
The principle of the method used is as follows: 5 When a particle carrying a charge e is
moving with velocity v across the lines of force in a magnetic field, placed so that the lines of
magnetic force are at right angles to the motion of the particle, then, if H is the magnetic force,
the moving particle will be acted on by a force equal to Hev. This force acts in the direction
which is at right angles to the magnetic force and to the direction of the motion of the particle. If
also we have an electric field of force X, the cathode ray will be acted upon by a force Xe. If the
electric and magnetic fields are arranged so that they oppose each other, then, when the force
Hev due to the magnetic field is adjusted to balance the force due to the electric field Xe, the
green patch of phosphorescence due to the cathode rays striking the end of the tube will be
undisturbed, and we have:
Hev = Xe
or
v = X/H.
Thus if we measure, as we can do without difficulty, the values of X and H when the rays are not
deflected, we can determine the value of v, the velocity of the particles. In a very highly
exhausted tube this may be 1/3 the velocity of light, or about 60,000 miles per second; in tubes
not so highly exhausted it may not be more than 5,000 miles per second, but in all cases when
the cathode rays are produced in tubes their velocity is much greater than the velocity of any
other moving body with which we are acquainted. It is, for example, many thousand times the
average velocity with which the molecules of hydrogen are moving at ordinary temperatures, or
indeed at any temperature yet realized.
Determination of e/m
Having found the velocity of the rays, let us now subject them to the action of the electric field
alone. Then the particles forming the rays are acted upon by a constant force and the problem is
like that of a bullet projected horizontally with a velocity v and falling under gravity. We know
that in time t, the bullet will fall a depth equal to gt2/2, where g is the acceleration due to gravity.
In our case the acceleration due to the electric field is equal to Xe/m, where m is the mass of the
particle. The time t = l/v, where l is the length of path, and v the velocity of projection.
Thus the displacement of the patch of phosphorescence where the rays strike the glass equals:
(1/2) (Xe/m) x (l2/v
2).
We can easily measure this displacement d, and we can thus find e/m from the equation:
e/m = (2d/X) x (v2/l
2).
The results of the determinations of the values of e/m [m being the mass of the particle] made by
this method are very interesting, for it is found that, however the cathode rays are produced, we
always get the same value of e/m for all the particles in the rays. We may, for example, by
altering the shape of the discharge tube and the pressure of the gas in the tube, produce great
changes in the velocity of the particles, but unless the velocity of the particles becomes so great
5 [In order to understand fully the following several paragraphs, the reader would need to have studied more about
electricity and magnetism—as you will in Senior Natural Science. However, for our purposes grasping the basic
outline of the argument will be sufficient.]
284
that they are moving nearly as fast as light, when other considerations have to be taken into
account, the value of e/m is nearly constant. The value of e/m is not merely independent of the
velocity. What is even more remarkable is that it is independent of the kind of electrodes we use
and also of the kind of gas in the tube. The particles which form the cathode rays must come
either from the gas in the tube or from the electrodes; we may, however, use any kind of
substance we please for the electrodes and fill the tube with gas of any kind and yet the value of
e/m will remain unaltered.
This constant value, when we measure e/m in the c.g.s. system6 of magnetic units, is
equal to about 1.7x107. If we compare this with the value of the ratio of the mass to the charge of
electricity carried by any system previously known, we find that it is of quite a different order of
magnitude. Before the cathode rays were investigated, the charged atom of hydrogen met with in
the electrolysis of liquids was the system which had the greatest known value of e/m, and in this
case the value is only 104, hence for the corpuscle in the cathode rays the value of e/m is 1,700
times the value for the corresponding quantity for the charged hydrogen atom. This discrepancy
must arise in one or other of two ways; either the mass of the corpuscle must be very small
compared with that of the atom of hydrogen, which until quite recently was the smallest mass
recognized in physics, or else the charge on the corpuscle must be very much greater than that on
the hydrogen atom. Now it has been shown by a method which I shall shortly describe, that the
electric charge is practically the same in the two cases; hence we are driven to the conclusion
that the mass of the corpuscle is only about 1/1,700 of that of the hydrogen atom.7 Thus the atom
is not the ultimate limit to the subdivision of matter; we may go further and get to the corpuscle,
and at this stage the corpuscle is the same from whatever source it may be derived.
Corpuscles very widely distributed
It is not only from what may be regarded as a somewhat artificial and sophisticated
source, viz. cathode rays, that we can obtain corpuscles. When once they had been discovered, it
was found that they are of very general occurrence. They are given out by metals when raised to
a red heat; indeed any substance when heated gives out corpuscles to some extent. We can detect
the emission of them from some substances, such as rubidium and the alloy of sodium and
potassium, even when they are cold; and it is perhaps allowable to suppose that there is some
emission by all substances, though our instruments are not at present sufficiently delicate to
detect it unless it is unusually large.
Corpuscles are also given out by metals and other bodies, but especially by the alkali
metals, when these are exposed to light.
They are being continually given out in large quantities and with very great velocities by
radioactive substances such as uranium and radium;8 they are produced in large quantities when
6 [This is the standard unit notation in centimeters, grams, and seconds.]
7 [Thomson’s estimation is fairly accurate. The currently accepted value for the mass of the electron is 9.1095 x 10
-31
kg, which is 1/1,836 the mass of the hydrogen atom.]
8 [At the turn of the century new elements were discovered that emitted “rays” (hence the name “radioactive”); some
of these rays turned out to be electrons.]
285
salts are put into flames, and there is good reason to suppose that corpuscles reach us from the
sun.
The corpuscle is thus very widely distributed, but wherever it is found, it preserves its
individuality, e/m being always equal to a certain constant value.
The corpuscle appears to form a part of all kinds of matter under the most diverse
conditions; it seems natural therefore to regard it as one of the bricks of which atoms are built
up9. . . .
[Thomson then presents a detailed determination of the electric charge carried by the corpuscle,
confirming that the mass of the corpuscle is about 1/1700 that of the hydrogen atom. The following is the
conclusion of the paper.]
In all known cases in which negative electricity occurs in gases at very low pressures, it
occurs in the form of corpuscles, small bodies with an invariable charge and mass. The case is
entirely different with positive electricity.10
* * * *
1. Given this understanding of the electron as a removable component of an atom, can we now
offer a clearer account of what happens in electrolysis? Consider the decomposition of water
in particular: Can you understand now what happens when the current flows?
2. Recall Morveau’s second and third principles for chemical naming: “Denominations should,
as far as possible, conform to nature of things…[and] a name that expresses nothing is
preferable to one which may express a false idea” (p. 65). Now that the atom seems to prove
divisible, have we done serious violence to the revolution in chemical nomenclature started
by Lavoisier, Morveau, and the others?
3. What (if any) of the original notion of the atom has been preserved through the development
of atomic theory that we have studied this year? To what extent has the atom proposed by
Dalton (or by Lucretius, for that matter) been shown to exist? Are Morveau’s fourth and fifth
principles significant in this matter?
9 [In 1899 Thomson had proposed that “ions”—electrically charged atoms—acquire their charge by the detachment
and attachment of electrons. In 1904 he improved upon Stoney’s attempts at explaining the spectra of elements—
i.e., the precise composition of the light emitted from a substance, which, as we saw with our flame tests, appears to
be distinctive of the element—in terms of the vibrations of electrons within atoms.]
10 [Thomson’s specialty was the conduction of electricity through gases. The electricity was carried by particles of
both negative and positive charges. In gases, the negative charges were all alike (electrons), but the positive charges
varied in mass and degree of charge depending on (among other things) what particular gas was present. These
positive “ions,” on Thomson’s 1899 account of ions, would be atoms that had lost one or more electrons.]