Priestley and “fixed air”

• Reported could obtain “fixed air” from fermenting vats in breweries because heavier than common air

• “Fixed air” and soda water– Soda water thought to be medicinal– Soda water available only at some mineral springs– Found “fixed air” dissolved in water produces soda water– Started a business producing artificial soda water from fixed air

Importance of Black’s Experiments• “Fixed air” [CO2] formed by /found in:

– heating mineral – burning of charcoal– fermenting organic matter– exhaled breath

• Similarity between animate and inanimate realm

• Gaseous substances given off by solids and liquids– could combine “fixed air” to produce chemical changes

• Applied quantitative measurement to chemical changes, (full maturity with Lavoisier)

Importance of Black’s Experiments• observations of crust formed when lime-water

left in open air – resembles limestone from which quicklime is made by

calcination

• deduced (correctly) small quantities of carbon dioxide in the atmosphere

• indication air not a simple substance – consisted of a mixture of at least two distinct

substances, ordinary air and carbon dioxide

Other “airs”

Cavendish and “Inflammable Air”

• Student of Joseph Black

• Published studies of inflammable air in 1766

• Made from iron, tin, or zinc

• in “oil of vitriol” [sulfuric acid] or “spirit of salt” [HCl]

• Vapor could be set on fire

• Clearly different from common air!

• 16.5 g zinc in oil of vitriol

• Weight before = 773.1 g • Weight after = 772.4 g

• Weight of inflammable air lost = 0.7 g

• 16.5 g zinc produces 5.9 liters of air

• 5.9 liters of common air weighs 7.3 g

• Inflammable air is 10.5X lighter than common air

The Density of Inflammable Air• Weigh “everything” before and afterwards

• Difference in weights = weight of air produced

Experimental Replications

Materials UsedDensity Calculated

(vs. common air)

Zinc in oil of vitriol 1 / 10.5

Zinc in oil of vitriol 1 / 10.3

Zinc in “spirit of salt” 1 / 11.1

Zinc in “spirit of salt” 1 / 11.2

Iron in oil of vitriol 1 / 11.2

Tin in oil of vitriol 1 / 11.1

Average 1 / 10.9

Is All Inflammable Air the Same?

• Density is the same, regardless of how made

- Iron, tin, or zinc

- Oil of vitriol or “spirit of salt” (hydrochloric acid)

• Explosive properties also the same

- Mixed inflammable air with common air

- Determined ratio producing most violent explosion

- Same ratio, whether made from iron, tin, or zinc

But what is inflammable air?

Why do things burn?

• Early Greeks element fire

• Alchemists principle of sulfur

Phlogiston – Cavendish’s inflammable air?

Phlogiston Theory• The Elements according to Becher (1669) and Stahl: Three Elements and Three Earths

• Fire, Air, and Water (as before)

• Sub-classified old concept of earth by different responses to combustion:

- Vitreous (inert) earth

- Combustible earth = phlogiston (Stahl)

- Volatile (distillable) earth

Combustion and Phlogiston

• Combustible objects rich in phlogiston

• After burning original substance minus phlogiston

• To restore original combustible substance – heat residue with something that burned easily – freed phlogiston combines with residue

Becher & Stahl Theory

• Place into airtight container [limited supply of air]– Flames extinguished

• air saturated with phlogiston– Mice die in airtight space

• air saturated with phlogiston

• Charcoal or wood – little ash after burning (nearly pure phlogiston)

• Ores smelted into pure metals – phlogiston transferred from charcoal  to ore

• Heat metals phlogiston released into air leaving calx

• Rusting of metal equivalent to burning of wood

Cavendish burns “inflammable air”

• One theory phlogistication produces “fixed air”

• Place into airtight container [limited supply of air]– Flames extinguished

• air saturated with phlogiston– Mice die in airtight space

• air saturated with phlogiston

• But, Cavendish showed:– Inflammable air + common air = explosion and what remained

didn’t cause precipitation of limewater [not “fixed air”]

What was it?

Problems with Phlogiston Theory

• Wood burns – ash lighter – loss phlogiston

• rusty metal (calx) heavier when phlogiston lost?

• Positive and negative weight phlogiston?

• combustion and rusting different versions of the same phenomenon?

combustion of wood – phlogiston leaves so rapidly it heats its surroundings and becames visible as flame

rusting -- loss of phlogiston slower and no flame appears

Problems with weight?• inaccurate measurements

• Weight changes only thought about solids

• Weight change = gases?

• Stahl Weight increase due to air entering metal to fill vacuum left after phlogiston escaped

• variation in weight an unimportant "accident“?

• phlogiston light, lightened substance containing it driving it out of metal naturally left residue heavier.

- only worried about existence

Explanations

• A good one from Cavendish Later

Phlogiston Theory• as experiments multiplied, became evident theory failed to

satisfactorily explain certain laboratory reactions.

• modifications introduced giving theory a flexibility to cover all cases

• modifications contradicted each others simple theory too cumbersome from number of modifications

• no satisfactory substitute better than anything before or could be suggested

• phlogiston theory cannot be said to have finally succumbed until the opening years of the nineteenth century

Need to think gases

• explanation of changes in weight during combustion due to gases that appeared or disappeared while the products were forming

• but no attempt in Stahl's day to take gases into account except to note their existence.

Need to think gases

• Before deficiency could be corrected, chemists had to grow more familiar with gases and the problems with confining for study.

• Rust heavier than metal, but had rust gained anything from the air? Not considered.

The Gases• Ash was lighter than wood what about vapors given off by burning wood? Not considered.

Joseph Priestly (1733 – 1804)

• Identified seven distinct airs: with “mercury trough”

• Lack of conclusions concerning his data

• Others made use of them in developing their theories

• Produced a brick-red “calx” when heated mercury in air

Priestley’s new ‘air’

• Discovered another form of air

• Mercury heated in air formed red substance – “the precipitate per se” or calx (= mecuric oxide)

• When heated with no air - calx changed back into mercury and gave off a gas with most unusual properties

• Mice were particularly active in the new air

• Priestley tried breathing some and found himself feeling “particularly light and easy for some time afterwards. Who can tell but that, in time, this pure air may become a fashionable article in luxury"

Priestley and “dephlogsticated air”

• Combustibles burned more brilliantly and rapidly in this gas

• A smoldering splint of wood thrust into a container of the gas burst into flame

• Priestley explained this phenomenon in terms of the phlogiston theory

• Splint of wood must given off phlogiston at a rapid pace

• The gas must have little or no phlogiston allowing it to accept the new phlogiston so easily

• Priestley therefore called his new gas "dephlogisticated air"

Priestley - “dephlogisticated air”

• Component of ordinary air

• Responsible for combustion

• Made animal respiration possible

Who discovered water?• Joseph Priestley

– noted when a mixture of hydrogen and air is exploded by means of an electric spark

– walls of vessel covered with moisture– a fact that he disregarded

• Cavendish – prepared water in measurable amount– got approximate figure for its volume composition

• Analogous conclusion reached about same time by James Watt, the Scottish engineer, and communicated to Priestley and to the Royal Society

Cavendish burns “inflammable air”

• Burned “inflammable air” + common air in closed container– No loss of weight– Inside of vessel became “dewy”– 423 measures inflammable air phlogisticated 1000 measures of

common air

• Cavendish went on to react dephlogisticated air with inflammable air – established optimal proportion as 2.02:1

• deplogisticated air +  inflammable air gives water

[now: 2 H2(g) + O2(g)  2H2O(l)]• Note:

– Cavendish still interprets in terms of phlogiston theory– Lavoisier rejects phlogiston theory interprets as evidence water not

a simple substance but product of the combustion of two gases – Hard blow at Greek theory of the elements

Cavendish and increase in weight of calx

Dephlogisticated air = (“water” – Φ)

Calx = [(earthy base of metal - Φ ) + “water” ] ↑ weight

Dephlogisticated air + inflammable air (Φ) = “water” or (Φ + “waterELEMENTAL”)

Heat calx Φ from “water” combines with calx (earthy base metal – Φ) to form metal

water devoid of Φ becomes dephlogisticated air

Lavoisier comes up with a simpler explanation !

Discovery of water on moon boosts prospects for permanent lunar base

• Since 1960’s – Apollo missions brought back first clumps of lunar soil and

rock – assumption moon dry– traces of water in samples thought to be contamination

picked up while being handled on Earth

• But– Data gathered from India’s $82 million lunar mission,

Chandrayaan I or “Moon Craft,” showed water formation may be an ongoing process on the moon, project scientists said Sept. 24

Water on the Moon

• Data from spacecraft found lunar soils became increasingly damp during sunlight hours, but dried out again at end of lunar day

• Cycles of damp-dry conditions suggest water is created on the moon every day

• How?– Protons spewed out by the sun (solar wind) collide with lunar

dust (regolith), that covers moon's surface

– Some of the debris grains contain oxygen

– interaction of the protons with this dust produces water, as well as small hydrogen-oxygen molecules (OH)

Discovery of water on moon boosts prospects for permanent lunar base

Moon water: Hydrogen ions carried from the sun in the solar wind may liberate oxygen from minerals in lunar soil to form water. At high temperatures (red-yellow) more molecules are released than adsorbed. When the temperature decreases (green-blue) water accumulates. Photograph: F. Merlin/University of Maryland

• On 9 October, Nasa crashed a probe called LCROSS (Lunar Crater Observation Sensing Satellite Mission) into the Cabeus A crater near the lunar south pole, in the hope of finding signs of water in the shower of debris it produces

http://www.youtube.com/watch?v=NQ8d2Oacv2M&feature=related