“free carbon.” its nature and determination in tar products

Apr., 1914 T H E J O U R N A L O F I iVDC-STRIi lL d l V D E S G I X E E R I S G C H E M I S T R Y 2 7 9

cents per t on for every 0 . z j per cent above r . j o per cent. The injustice of this practice is very e r ident as i t often happens tha t coals with a high sulfur content are extremely high in heat value and do not clinker readily at all. Since the sulfur has no appreciable effect upon the metallic par t s of t he furnace, it need therefore not be considered in the selection of a coal for steaming purposes.

To-ar r ive a t t he value of a coal for steaming purposes it is therefore just as essential t o make t h e fusing temperature test of the ash as i t is t o make the calorimetric determination. If these determinations are made an explanation is readily had as to why two coals of apparently like proximate analyses will give entirely cliff erent evaporations when fired under like conditions.

50 E4ST 41sT STREET, NEW I’ORK

“FREE CARBON” Its Nature and Determination in Tar Products ,

By JOHN MORRIS WEISS Received January 26, 1914

-411 tars contain a substance in greater or lesser amount . which has been called “free carbon.’’ This has usually been considered as the material insoluble in hot benzol, and is not pure elemental carbon, bu t a mixture of this substance with insoluble hydrocarbons and other compounds of high carbon content. The amount of this free carbon varies quite considerably in ta rs from 7-arious sources, depending on the original coal and also! t o a large,extent, on the temperature of carbonization and the degree of superheating to which the developing t a r r apor s were subjected. Under like conditions, t h e higher t h e temperature the greater the amount of free carbon found in the t a r produced. The extent t o which free carbon varies in ta rs from various sources may be shown in the following typical analyses of a number of ta rs :

Percentage Iree carbon b y

KINDS OF TAR toluol-benzol method Semet-Solvay coke o v e n . . . . . . . . . . . . . . . . . I O 76 Koppers coke o v e n . , . . . . . . . . . . . . . . . . . . . 6 79 United Ot to coke o v e n . . . . . . . . . . . . . . . 13 18 Horizontal retort gas w o r k s . . . . . . . . . . . . . 3 ; 4 i Horizontal re tor t gas w o r k s . . . . . . . . . . . . . . . 28 91 Inclined retort gas works. . . . . . . . . . . . . . . 24.31 T-ertical retort gas v o r k s . . . . . . . . . . . . . . . 3 95 \Vater g a s . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 02 Water g a s . , . . . . . . . . . . . . . . . . . . . . . . . . 0 . i R Oil gas t a r . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 , 1 8 Blast furnace . . . . . . . . . . . . . . 15 .89 Ligni te . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. i 9 Hardffood. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 . 0 2 Pine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 . 0 3

,411 these analyses were taken on t h e dried tars, t h a t is, the samples of t a r were distilled until all water was removed, a n y oil distilling with the water being separated and returned t o the distilling vessel after t he water was completely driven over.

As s ta ted before, this insoluble material is no t pure carbon. One analysis b y Donath and Asriel’ showed

Hydrogen , . . . . . . . . . . . . . . . . . . . . . . 2 . 3 S i t r o g e n . . . . . . . . . . . . . . . . . . . . . . . . 3 , 7 Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . 7.13 Carbon . . . . . . . . . . . . . . . . . . . . . . . . . 8 9 . 2

This analysis adds up to over 100, bu t t he writer can

give only the figures as found by him in the reference. Hubbard a n d Reeve’ h a r e made several ultimate analyses of so-called free carbon, with the following results :

From TO Carbon. . . . . . . . . . . 90.17 94 26 Hydrogen 2 59 3 . i l Oxygen . . . . . . . . . 1 . 8 1 5 91 Sulfur . . . . . . . . . . . . . . . . 0.50 1 7 8 Nitrogen . . . . . . . . . . . . No trace upon a qual-

i tat ive test.

They also made analyses of sulfur on various precipitates obtained by digestion of ta rs with carbon bisulfide for various periods, the results seeming t o indicate a combination of t a r with the solvent.

One analysis of average free carbon from coal t a r s made in the writer’s laboratory showed

Carbon . . . . . . . . . . . . . . . . 89.85 Hydrogen . . . . . . . . . . . . . . 3 . 3 0 S i t r o g e n . , . . . . . . . . . . . . . . . . 1 . I O Oxygen. . . . . . . . . . . . . . . . . . . 3 . 1 7 (by difference) Sulfur . . . . . . . . . . . . . . . . . . . . 1 28 hlineral a s h . . . . . . . . . . . . . . . 1 . 3 4

The free carbon used for this analysis was obtained by the toluol-benzol method, which is described in detail in a later par t of this paper.

illany methods have been proposed for t he estima- tion of free carbon. Kraemer2 extracts t he t a r with forty times i ts volume of xylol. Kohler3 heats I O

grams of t a r with 2 j grams of glacial acetic acid and z j grams of toluol, pour; t h s mixture on two filters of equal weight placed inside of each other, and washes with hot toluol until ~?olorless. Kraemer and Spilker4 mix the t a r with twenty par t s of xylol, filter off the insoluble material, wash with five parts of xylol, and dry on t he filter. The same authors give another method which consists of mixing one pa r t of t a r with three par t s of aniline, pouring t h e liquid mass on a porcelain plate of special shape. The insoluble carbon remains as a heavy mass after t he liquid has been sucked into the porcelain and is removed with a wooden spatula, dried and weighed. The statement is made tha t this method gives from 2-3 per cent lower results t h a n the xylol method described, due to the greater solubility of the t a r bitumens in aniline. Hodurekj has found t h a t some solvents, of which benzol, acetic acid and ether are mentioned, have a precipitating action on bituminous substances, such as those contained in coal t a r , and has devised a method based on filtration of t he original undiluted t a r t o determine the real free carbon. The method is, however, cumbrous and not adapted for practical work.

Hubbard a n d Reeve,G after a comparison of various methods, proposed the use of cold carbon bisulfide as t he solvent in testing t a r s for free carbon. The method was claimed t o be equally applicable t o both t a r and asphalt products. These authors also make mention of the progressive formation of further insoluble mat te r when the filtrates are allowed t o s tand ,

1 Proc. Am. SOL. Test ing Mater ia l s , 11 (1911), 665. 2 1,unge’s “Coal T a r a n d Ammonia,” 4 th ed., p . 426. a Z. a n g e u . Chem. (1888), 677 . 4 Muspral t ’s Indus. Chem., 8 (1900). 3 . 5 Oesterr. Chenr. Z e i t . (1904), 365.

Lunge’s “Coal T a r and Ammonia,” 4th ed., p. 241. 8 Pyoc. A m . SOL. Test ing .Wuterials, 10 (1910). 420.

2 8 0 T H E JOC‘RIVdL O F I - V D r S T R I d L ALVD EAVGIATEERING C H E X I S T R Y Yol. 6 , KO. 4

and ascribe this phenomenon either t o sedimentation or t o a combination of t a r and solvent. S. R. Church, i n discussing this paper, objects t o the use of this method for testing t a r products, contending tha t for these materials t h e use of two solvents is desirable, a n d t h a t a ho t extraction is necessary. The method suggested by him a n d later published in connection with other methods for testing tars, oils a n d pitches,’ involves the use of toluol and benzol, and mill be fully described in a later portion of this paper. Later, Church2 described a n improved form of extraction appara tus , a modification of one proposed for other uses by H. J . C a r y - C ~ r r . ~

Recently, in a book published by Arthur R . W a r n e ~ , ~ there is described a method devised b y Hooper and a modification of same b y Warnes. This method involves the use of cresylic acid and 90 per cent benzol, and the writer has had no experience in i t s use, bu t objects t o 90 per cent benzol and cresylic acid as solvents, because they are not definite chemical compounds which can always be obtained pure.

The remainder of this paper may be roughly sub- divided into three parts. The first concerns work on t h e formation of insoluble compounds in mixtures of t a r products a n d various solvents. The second comprises a comparison of various methods for “free carbon” or insoluble material determination, t he work involved being carried out on a number of materials, bo th of pitch and asphaltic origin. The third portion involves a detailed description of t he toluol-benzol “free carbon” method as developed in our laboratories, for t a r and t a r products, and decided after considerable experience and experimentation as t h e most convenient.

I - INSOLUBLE C O M P O U N D S F O R M E D IPj U I X T U R E S O F

T A R P R O D U C T S A X D V A R I O U S S O L V E X T S

The experiments which are set forth in the first par t of this communication were originally undertaken for t he purpose of obtaining a t a r free from insoluble residue, without otherwise changing the chemical constitution of t he ta r . As will be seen later, t h e a t t empt s t o this end were unsuccessful. bu t t h e results were very interesting, a n d led to the further experiments outlined below.

T o remove free carbon, chloroform was first used as a solvent, because i t s low boiling point renders it easy t o remove without superheating. Moreover, i t has a n odor distinct from t h a t of t he aromatic hydrocarbons, a n d i ts removal could be more or less ac- curately indicated by the odor of t he residues handled. T h e t a r selected was a coke oven t a r , containing about j per cent of insoluble mat te r when tested by the toluol-benzol method. A weighed quant i ty of t a r (about joo grams) was diluted with about t en t imes i ts volume of pure chloroform and filtered twice through weighed thimbles made of a double thickness of S. and S. No. 5 ~ j hardened filter paper. When all material had been passed through t h e thimbles, these

THIS JOVRXAL, 3 (1911), 2 2 7 . I b i d . , 6 (1913), 19.5.

3 Ib id . . 4 (1912), 535 and 856. 4 Warnes’ “Coal T a r Distillation,” p. 146

mere placed in the extractors a n d exhausted with hot chloroform. The extracts were refiltered through fresh thimbles, and again extracted. X11 the thimbles were dried a t 100’ C. a n d weighed. The combined filtrates and washings were brought into a t a red flask connected t o a condenser, and the bulk of t he chloroform taken off on a s team ba th . The condenser was then disconnected and the material was held at a temperature of 80’ C. until it had regained i ts or;ginal weight, less the amount of insoluble matter removed. This latter amounted t o j.54 per cent. ilt this point, all odor of chloroform had completely disappeared.

This supposedly carbon-free t a r was then tested by the toluol-benzol method, and also by a chloroform extraction t o determine t h e percentage of insoluble mat te r . The results were:

Original

5 . 5 4 5 . 3 6

Percentage insoluble in tar Trea ted tar Toluol and benzol . . . . , , . , . . . . Chloroform, . . . . . . . . , .

, , , 10.05 0 . 8 8 . . , , ,

The inference to be drawn is obvious. On standing, chloroform formed a compound with the t a r which is insoluble in benzol. This insoluble material is quite different in appearance from ordinary free carbon. The latter is dull black, a n d infusible, m-hile this substance had considerable luster and could be sintered together by careful heating. Under. t h e microscope it appeared slightly crystalline. No quantitative test was made on this substance, bu t on oxidation with fuming nitric acid, a very strong qualitative test mas obtained in the resulting solution.

Following this, a similar amoun t of t h e same t a r was treated in like manner, using pure benzol (benzene) as t he solvent instead of chloroform. The tests of this treated t a r mere:

Percentage insolu1,le in

Toliiol and b e n z r l . , . . . , , . . . . . 4 . ; 1 Benzol a lone . . . . . . . 4 . 6 i

. . . 2 li Chloroform. . . . . . . , ,

. . . . . . . . . . . . . . . . .

This residue also did not resemble ordinary free carbon, being brown instead of black. Under the microscope, i t appeared absolutely amorphous. On heating. it melted with decomposition and coking.

Slides were made of t h e original and treated tars, and viewed in a very t.hin layer with the microscope by transmitted light. Similar slides were also made, mixing- a drop of one of t he t a r s with n drop of t he solvent. The magnification used was eighty-seven diameters. This examination confirmed the analytical tests, and threw further light on the subject. The results are given in the following table. The body of t h e slides appeared a clear, reddish bron-n. with the l-ariations as noted in the following table.

The apparent meaning of the following results is t h a t in the treated t a r s there is no real insoluble material of t he same na ture as ordinary free carbon. bu t t h a t apparently materials have been formed which, though soluble in the complex mixture known as t a r , yet are precipitated upon t h e addition of a solvent. These results indicate t h a t both chloroform and benzol in contact with t a r undoubtedly form compounds with some of t he t a r constituents, which compounds are a t

=Ipr., 1914 T H E J 0 C R N A L 0 F I -V D U S T R I A L A D E JVGI S E E RING C H E M I S T R Y 2 8 I

SLIDE h-0. M A T E R I A L APPEARANCE benzol and toluol were made, using carbon bisulfide l . . . . . .

1 _ . . . . . . 3 . . . . . . 4 . . . . . . 3 . . . . . .

b . . . . . .

8 .

9

Original ta r

T a r treated with chloroform T a r treated with benzol hlixture of h70 1 and benzol Mixture oi No. 1 and chloro-

Mixture of No. 2 a n d benzol .\fixture of h-0. 2 and chloro-

hlixture of h-o. 3 and benzol

hlixture of IXo. 3 and chloro-

form

form

form

Very graniilar with amorphous

Clear, without grains. Clear, a i t h o u t grains. Strongly granular.

Strongly granular. Yery strongly granular.

S e a r l y clear. Granular and slightlr crystal-

grains of various sizes.

line.

Granular and fine, needle-like crystals.

least partly insoluble in benzol. and to a lesser degree, in chloroform. These three tars were also tested for fixed carbon and ash.

Percentages fixed carbon .Ish

Original t a r . . . . . . . . . . . . . . . . . . . . . . 15.42 0 . 1 3 Chloroform treated t a r . . . . . . . . . . . . 14.65 0 .02 Benzol treated t a r . . . . . . . . . . . . . . . 13.78 0 . 0 1

These results are also indicative. as t he fixed carbon mas not lowered as much as would be expected from the removal of over j per cent of material nearly all carbon. It would tend t o show t h a t simultaneously, higher, more complex bodies were formed which, on heating, give a n increased coke residue. Possibly the

and chloroform separately. t he material under trial being used both in the digestion anti in t h e extractor. The following results were obtained on the same t a r t h a t was prex*iously used:

Percentage Insolublr in Time o i standing insoluhle in chloroform carbon bisulfide

0 2.5 hour . . . . . . . . . . . . . . . . 5 . 9 1 5 .84 48 hours . . . . . . . . . . . . 6 . 3 3 6 .62

120 hours . . . . . . . . . . . . . . . 8 . 2 7 i.37 216 hours . . . . . . . . . . . . . . . . 8 . 0 1 7 . 6 7 258 hours . . . . . . . . . . . . . . . . . 8 . 2 1 7 . 5 2

d similar increase in apparent insoluble mat te r was noted here as with benzol and toluol, though not t o the same extent.

The residues from the chloroform extraction \yere tested qualitatively for chlorine with positive results, bu t a.s no tube furnace was available, quantitative results could not be obtained. On t he other hand, t he residues from the carbon bisulfide extractions were assayed for sulfur by the “Eschka” method, t h e following figures being obtained:

Time of Percentage Residue f rom a standing sulfur

Benzol extraction. . . . . . . . . . . . . . . 0 . 9 2 Carbon bisulfide extraction.. . . 0 , 2 5 hr. 1.46 Carbon bisulfide extraction, , , , 120 hrs. 1 82 Carbon bisulfide extraction.. . . 216 hrs. 1 .67

chloroform may also form bodies of a tr ialkylmethane series. which would have this tendency t o a very marked degree. It was not thought worth while t o subject these residues t o a n ult imate quantitative organic analysis, as with a n evident mixture of compounds, such results would show bu t little.‘

I n t h e light of t he foregoing results, experiments mere then insti tuted t o see whether, in t he laboratory determination of free carbon, t h e results obtained would increase with t h e t ime the solvent and t a r were allowed to remain in contact in the cold. The same

This is conclusive proof t h a t t he solvents actually enter into combination with the t a r constituents. The results can be explained on no other basis.

Xt various times, t he writer has noticed in some of t he German publications on t a r products, t ha t aniline, pyridine and glacial acetic acid have been suggested as t h e digestive solvent for free carbon determination. The following results were obtained using the material mentioned for digestion, and then in all cases after filtration. using benzol in the extractor:

t a r was used for this work as in t h e previous experiments. Except for t he t ime of standing with the fir-st amount of solvent added, t he general procedure in all cases was identical. In one series of tests, toluol was used as the digesting solvent; in another, benzol. I n both cases benzol was used afterward in t h e extractor.

Percentage Insoluble in Time of s tanding insoluble in benzol toluol and benzol

0 . 2 5 hour . . . . . . . . . . . . . . 6 . 4 2 5 54

90 hours . . . . . . . . . . . 7 . 7 4 i , 5 5 138 hours . . . . . . . . . . . . 9 . 2 5 8 . 4 4 258 hours . . . . . . . . . . . 10 7 2 9 . 3 4

24 hours . . . . . . . . . . . . . . 6 . 6 5 6 . 3 0

The longer the t a r stands, t h e greater t h e amount of insoluble residue obtained. The reaction is evidently accelerated by the presence of a large excess of the solvent, and occurs equally with benzol and toluol. With only small amounts of benzol present, such as in an ordinary t a r . i t is conceivable t h a t this reaction might take place with a 1-ery small 1-elocity. I n other words, with long t ime the amount of apparent insoluble mat te r in a t a r might increase.

Experiments were then insti tuted by the writer t o see whether carbon bisulfide and chloroform would give similar results. Tests similar to those with

Percentage free carbon b y digestion with

Aniline Pyridine Glacial acetic Time of standing and benzol and benzol acid and benzol

0 .25 hour . . . . . . . . . . . 5 . 0 0 5 . 1 1 6 . 8 0 48 hours . . . . . . . . . . . 4.81 5 . 2 3 7 .01

144 h o u r s . . . . . . . . . . 4.62 5 . 2 7 8 . 10

Here quite different results were obtained in the case of t he first tm-o solvents, aniline and pyridine. -4cetic acid gives high results, and shows t h e phenomenon of progressive formation of insoluble compounds. It was also noted t h a t , owing t o i t s hygroscopic nature, water is easily absorbed and in this elrent, precipitates are formed which dissolve very slowly in the extractor. The pyridine is a very disagreeable substance with vh ich t o work. and is expensive and difficult t o obtain in the pure s ta te . The filtration of t he aniline solution is a very slow and tedious operation, from four t o five hours being required in many cases t o pass j o cc. through the thimble. I n spite of t he theoretical aspects of t he matter: neither pyridine nor aniline seem to the writer t o be suitable materials for a laboratory assay of free carbon.

I t was then deemed advisable t o t r y further experiments on various t a r products. So far, bu t one t a r had been used, and i t was possible t h a t this was a

282 T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Trol. 6 , KO. 4

peculiar material, giving rise t o phenomena not shown b y other similar substances. A series of experiments on various materials was made, comparing aniline a n d toluol as t he digesting solvents, and using benzol afterward in t h e extractor.

Aniline Toluol 7

Time of digestion 0.25 hour 7 2 hours 0.25 hour 7 2 hours Coal t a r No. I , , . , , , 3 .22 3 .71 5 . 0 9 5 . 3 1 Coal tar KO. 2 , . . , , , 12 ,48 12 .53 14 .28 1 7 . 5 9 Coal t a r pi tch, , . , , , 8.68 9 08 13.22 1 5 . 1 5 Xl'ater gas t a r . . . . . . . 0 , 0 2 0 . l i 0 . 0 2 0 . 1 9

Besides, several substances were tested a t 0 . z j hour only, using aniline versus toluol:

Aniline Toluol

Water gas tar p i t c h . . . . . . . . . . . . . . 4.11 5 . 2 8

Coal tar briquette p i t ch . . . . . . . . . . 17.30 21.13

Road compound , . . . . . . . . . . . . . 11. R 8 13 .95

Various filtrates f rom this last set of tests mere examined under the microscope by the hanging drop method. With both aniline and toluol, t h e first few drops filtered showed a very faint trace of insoluble ma t t e r ; t he remainder of t he filtrate was in both cases perfectly clear when examined immediately. The aniline filtrate remained so, even after twenty-four hours 'standing,but t h e toluol filtrates showed a gradual formation of insoluble mat te r in the form of amorphous grains. The formation of this precipitate was accelerated by further dilution with either toluol or benzol. The aniline solutions, similarly diluted, also showed precipitation, b u t of a quite different nature, being in the form of clear, fine, crystalline needles. The toluol filtrates showed precipitation on standing alone, t he aniline filtrates only after t h e addition of benzol.

These results are of t h e same general nature as those with the first t a r investigated. I n water gas t a r products, where the insoluble residue is very small, t he differences between toluol and aniline are not marked. T a r No. I , which shows no increase on standing with toluol, was unusually high in t a r acids, a n d this factor may be the cause of i t s variable behavior. With substances varying as much as ta rs do, i t would be too much t o expect t h a t all varieties would behave in exactly t h e same way, and i t seems sufficient t h a t a majority of those investigated showed similar phenomena when mixed with various solvents. For a practical laboratory test , neither aniline nor pyridine seem suitable. The latter, as before mentioned, is very disagreeable in i ts properties, expensive, and difficult t o obtain pure. The difficulty of filtration of t he aniline solutions is, t o t he writer's mind, sufficient in itself t o exclude it from consideration for such purposes. Such difficulty is not en- countered with toluol, carbon bisulfide, chloroform, etc. For a working method i t would seem imperative t o consider solvents of t he general na ture of these materials.

Coal tar roofing pi tch. . , , , . . , . , . . 2 5 . 5 i

Coal tar pav ing p i t ch . . . . . . . . . . . . 13.08 1 6 . 7 2

20.51

11-CODIPARISOK O F V A R I O U S MORE O R LESS W I D E L Y USED M E T H O D S F O R DETERMI&-ATION O F I N -

SOLUBLE M A T T E R

A. Cold carbon bisulfide method, using a Gooch

crucible-standard procedure of the American Society for Testing hlaterinls.'

B . Toluol-benzol hot extraction method, using a cup made of filter paper.

C . S tandard A. S. T. 11. method, using cold carbon tetrachloride as the solvent.

D. Themethod used in C was supplemented by a hot extraction with the same solvent.

Besides these tests. another set was carried out, using carbon tetrachloride and cups of filter paper, and running exactly as in the toluol-benzol method. These results are not recorded because t h e experience was t h a t results obtained by this procedure are not reliable, especially with t a r products. d f t e r extraction and drying, t he thimbles become very brittle and cannot, i n many cases, be handled without loss. I n some cases, also, with substances low in insoluble matter, a n appreciable gain in weight was noted. The hot solvent and bitumen seem to form some compound which attacks the filter paper and causes dis- integration. This is probably hydrochloric acid or chlorine compounds of some sort. An acid reaction was noted in the extraction flasks and in the recovery of carbon tetrachloride; t he residues in the distillation vessel had a s-ery strong smell of hydrochloric acid. This phenomenon was not exhaustively investigated, so t h a t no positive assertion as t o the cause can be made. In these experiments, eighteen materials, com-

prising t h e most common types of pitches and asphalts, were selected and tested b y the four methods mentioned above. All tests were made in duplicate, making 144 single determinations. The work was carried out b y a single operator, and great care was taken t o have as nearly as possible identical conditions i'n all cases. The solvents used were chemically pure, of t he best obtainable grade. Thoroughly average samples of t h e various bitumens used were taken for t h e single determinations. I n other words. e\-ery precaution was taken t o eliminate all variations except those inherent in the particular method employed.

T h e results are given in the following table, two figures being given under each method, and repre- senting the check determinations. The general con- sistency of t he various materials was about 40' Dow taken a t 7 7 ' F. for five seconds, under a load of IOO

grams.

It was necessary in these tests t o alter slightly the cold carbon bisulfide method when t a r products were being handled. The slow solution of t h e last portion of these bitumens made complete washing a long and tedious affair. Accordingly, after the bitumen had been entirely brought into the crucible, the washing was carried on until about 150 cc. of carbon bisulfide had been used. The crucible was then allowed t o s tand over night in a stoppered bottle containing carbon bisulfide to a depth of about half t he height of the crucible. Following this digestion, t he washing could be completed with the use of jo-IOO cc. addi- tional carbon bisulfide. Precisely t h e same procedure

P~oc. A m SOL Teslinr Malerials, 11 (1911) 245.

T H E J O C R X A L O F I i V D C S T R I d L A S D ENGI-VEERING C H E M I S T R Y 783

4 S T &I. method cold CS2 Benzol to1 hot eYtr CCId cold Gooch CC14 hot Gooch

Coal t a r pitch, horizontal gas re tor t . . . . . . . . Coal t a r pitch, inclined gas r e t o r t . , , . . , , . . , ,

Coal t a r pitch, vertical gas r e t o r t . . . . . . . . . . . Coal tdr pitch, coke o v e n . . . . . . . . . . . . . . . . . . Coal ta r pitch, coke o v e n . . . . . . . . . . . . . . . . . . R‘ater gas ta r p i t c h . . . . . . . . . . . . . . . . . . . . . .

Blast furnace t a r p i t c h . . . . . . . . . . . . . . . . . . . . . Pine ta r p i t c h . . . . . . . . . . . . . . . . . . . . . . . . . . . Stearirie p i t c h , , . . . . . . . . . . . . . . . . . . . . . . . . Bermudez asphal t . . . . . . . . . . . . . . . . . . . . . . . . Trinidad asphal t . , . . . . . . . . . . . . . . . . . . . . . . . Gilsonite fluxed.. . . . . . . . . . . . . . . . . . . . . . . . . . Grahamite fluxed. . . . . . . . . . . . . . . . . . . . . . California asphalt . . . . . . . . . . . . . . . . . . . . . . . . Xexican aspha!t . . . . . . . . . . . . . . . . . . . . . . . . . Texas blown asphal t . . . . . . . . . . . . . . . . . . . . . . Texas straight run asphalt . . . . . . . . .

\Vater gas t a r pitch . . . . . . . . . . . . . . . . . . . . . .

1 2 34.76 32.07 10 .16 19.83 1T.26

2 . 0 2 1 . 6 0

30 .20 4 68 4 .61 5 . 4 9

2 4 , 3 8 0 . 1 4 0 . 1 2 0.46 0 . 3 0 1 . 1 1 1.25

35.05 31.95 10 .4 i lY.64 1 7 . 4 7

1.98 1.46

29.70 4.60 4.70 5.43 24.43 0.3; 0.12 0.45 0 .29 I .33 1.36

was necessary when carrying on the cold carbon tetrachloride tests.

Comparing the figures obtained by the hot toluol- benzol method with those of t he cold carbon bisulfide method, i t will be seen t h a t for t he coal tar products in general, approximately the same results are obtained. The one exception is t h e vertical retort t a r pitch, which is notably higher by the cold carbon bisulfide test . The water gas t a r pitches give markedly higher results when tested by hot toluol and benzol, a phenomenon which must be explained by the nature of these bitumens, xh ich are quite different from coal t a r products. The pine t a r pitch is also lower by the carbon bisulfide test i n somewhat lesser ratio t h a n the water gas t a r products, bu t nevertheless. striking. All t he asphalt products show approximately the same results b y both methods, except t he Trinidad asphalt. which gives slightly lower figures by the hot extraction with toluol and benzol.

Mention may also be made here of stearine pitch and i ts behavior in these tests. I t dissolves with great difficulty in all of t h e solvents used, forming gummy masses which were very difficult t o filter, and which were broken up only by long washing. The final residue was not “free carbon’’ i n the ordinary sense of t he word, bu t was a somewhat clastic, bituminous mass, which could be melted with decomposition at a n elevated temperature. The results with benzol and with carbon tetrachloride on this material were so unsatisfactory and showed such poor concordance t h a t they were omitted as n-orthless.

The cold carbon tetrachloride test , in all cases on t a r products, gave much higher figures than those obtained with the other solvents used. The hot extraction gave lower results t h a n with the cold solvent, b u t in no case as low as the results with carbon bisulfide or toluol-benzol. On the asphalts there is very little difference between the hot and cold solvent, and only minor variations between this material a n d the other solvents employed.

The carbon tetrachloride methods have never been considered as basic methods for a n insoluble mat te r determination, bu t merely a s a supplementary procedure t o determine something of t h e na ture of the bitumens soluble in’ other solvents. Therefore, i t

’ -7 7, --_\

1 2 1 2 I 7

34.50 35.3c 42.41 42.26 3S.ii 37 94 30.59 30.67 3 8 . 2 2 38.95 34.78 34,8.5 T 80 8.09 1 7 . 2 5 17. 5 0 15.38 1 5 . 9 0

20 92 71.31 30 38 3 1 . 7 5 2 i . 2 4 2i.01 18.40 18 .26 25 97 26 .50 23.09 23.41 4 . 7 3 5.19 10.31 10.76 9.02 9.21 T.92 7.71 14.83 13 .31 11.93 11.77 28.76 27.95 34.87 35.32 32.82 3 1 . 3 1

8 .00 i . 5 9 11.67 11.47 11.41 10.97

5 ‘ 3 5 . 7 0 5.73 5 . 7 8 5 .61 5 7 1 22.21 12.56 23.34 23.89 22.30 21.17 0 04 0 . 0 7 0.23 0 29 0.24 0.26 0.0 0.0 0.37 0.32 0.30 0.32 0 . 2 ; 0.39 u.43 0.41 0.43 0.41 0. i i 0 47 0.30 0.40 0.30 0.40 1.26 1.36 1.13 1 .OY 0.96 a0.96 1.71 1 84 1.83 1 . 5 1 1.85 1.4s

, . . . . . . . . . . . . . . ( c j

( a ) Not considered worth recording.

would not seem necessary to consider i t as a possible solvent for regular “free carbon” tests of t a rs and pitches. The writer will, therefore, confine himself to a consideration of t he relative merits of t h e cold carbon bisulfide test and the toluol-benzol hot extraction.

On asphalts in general, t he Gooch method using carbon bisulfide can be completed in a considerably less t ime than the toluol-benzol hot extraction, and the results obtained are equally as accurate. For this class of bitumens alone, i t seems t o be considerably more convenient. But i t must not be forgotten t h a t t he toluol-benzol method can be used with accuracy on asphalts, and even though i t consumes a longer total time, yet the actual t ime required for t he operator is no greater. The extractor, once started, needs no especial attention. The carbon bisulfide cold method .is, however, not readily applicable to t a r products. I t is troublesome and slow. ,411 our experience tends t o show t h a t a cold solvent is not desirable for t a r s and pitches. For these materials, the hot toluol- benzol method is far more convenient and easy of application, and the writer has no hesitancy in rec- ommending i t . An aromatic solvent is the natural solvent for t a r products, made up as they are of mainly aromatic compounds. Toluol and benzol are aromatic solvents, in fact, t h e only ones of this series low enough boiling to be applicable to this purpose.

IIt--“ F R E E CARBON” M E T H O D RECOMMENDED

The writer would now tu rn his attention t o a detailed description of t he “free carbon” method rcc- ommended, using toluol and benzol as solvents. This method in all i ts essential details has been in use in all of the laboratories of t he Barrett Manufacturing Company for a period of years, and has been adopted by a number of outside laboratories. So far as accuracy of results and case of manipulation is concerned, i t has, t o the best of my knowledge, given satisfactory results. V h e n t h e method was first proposed in essentially i ts present form, check tests on s tandard samples were made b y six of our principal laboratories.

These results seem particularly good when one con- siders t h a t these tests were undertaken when the method was first introduced, at which t ime the opera-

284 T H E J O U R N A L 0 F I LIT D L'S T R I A L

Percentages of free carbon in

Laboratory 1 . . . . . . . , . . . Laboratory 2 . . . . . . . . . . Laboratory 3 . . . . . . . . . , . Laboratory 4 . . , . . . . . . . . Laboratory 5 . , . . . , . . . . . Laboratory 6 . . , . . , . . , . .

Coal ta r pitch

No. 1 . . 2 3 . 4 0 . . 24 .26 , , 23 .40 , . 2 3 . 4 1 . , 24.03 , , 2 3 . 7 0

Coal tar pitch

l i o . 2 38 13 36 4 4 39 .40 40 . i 9 4 0 . 7 1 38 .43

Coal tar N o . 1 2 8 . 6 7 28 .61 28.80 29.52 2 9 . 2 7 29 .49

Coal tar iY0. 2 1 2 . 2 4 1 3 . 3 1 13 .30 1 5 . 2 6 1 3 . 4 8 13 .19

tors in the various laboratories were not yet expert in the manipulation of the method. At present, much closer checks could be obtained, and such discrepancies as T a r No. 2 , Laboratory 4, would be entirely obviated. Since this time (about five years ago) the principal changes have been in the form of the extractor, the s team ba th , and supplementary apparatus. Following the results given in the early par t of this paper, the operator should be cautioned against allowing the pitch or ta r t o digest too long with the toluol. At t h e outside, thir ty minutes should suffice. This feature may have caused some of the discrepancies in check testing on the high side, as a t the time of first putt ing forward this test , the possibility of formation of insoluble compounds was not recognized. All details of the test as standardized today, together with full descriptions of all apparatus used, are included in the following paragraphs.

A P P A R A T U b

The extractor is shown in Fig. I , and is patterned The principal

Water /a+- differences are in the c 0 n c f e n s e r y e-+ dimensions, the flask

after one described b y H. J . Cary-Curr.'

being inside diameter a t the top, z 1 L'' diameter at the bottom and@ / in height. The t in top and coil are made larger a t the top to correspond t o the flask and the sides of the top have been given an outward slant t o prevent any water condensing on the top being carried into the extractor flask. On the lovver side of the top are t n o small hooks to hold the wire

__ carrying the p a p e r thimble. The wire

f o R basket has been made of German silver wire.

- . - _ ..

r R ~ E

and its construction requires but litt'le ingenuity on the part of the operator.

Any type of steam or hot water bath will suffice for heating. We have, however, constructed in our own shops a bath for this purpose. which is very satisfactory in operation and , being compact, takes up very little space. It is constructed of copper and consists of a rectangular box eighteen inches long by five inches high. The width varies, depending on the number of extractors to be provided for. For an eight-extractor bath, a width of ten inches would be

FIG I

1 THIS JOURKAL. 4 (1912), 535 and 856.

ALVD EL\TGIA\7EERI~VG C H E M I S T R Y Vol. 6 , S o . 4

used. Half way up from the bottom of the box is a perforated false bot tom, on which the extraction flasks rest. Below this false bottom is a steam coil, entering and leaving through the side of the box. This coil is made of 3 t ' 4 inch copper pipe, strong enough to withstand the local steam pressure. An S bend through the box, giving about jq inches of pipe, is ample. The top of the box contains tyo rows of four circular holes each, the openings having a diameter of two and seven-eighths inches. At each corner of the box are uprights carrying a plate of copper the same size as the top of the box, and six inches above i t . This plate is cut out with openings directly over those on the top of the box and of the same size, this arrangement serving t o steady the flasks. Four condensers are used in series, so tha t a t one end of the box there is provided a water inlet with cock for each row of flasks. The box is filled with water, and the coil keeps this water hot enough t o boil the benzol in the extraction flasks. The gradual evaporation of the water is taken care of by a constant level device a t the opposite end from the condenser water inlets. The spent water from the condensers drains into this constant level device. and by this means sufficient

FIG I1

water is added automatically t o replace t h a t lost by evaporation. There is a draw-off a t the bottom of the bath for cleaning purposes. The connections of the condensers are made with rubber tubing. The Ixhole outfit can be placed on brackets on the r a l l with na te r and steam connections, and takes up but little space. X picture of one of these baths in use is s h o n n in Fig. 11.

The filter cups or thimbles are made of Schleicher & Schuell No. j 7 j hardened filter paper, which comes in cut circles. The size used is I j cm. in diameter. T o make a cup, two circles should be taken and one cut down t o a diameter of about 14 cm. A round stick about one inch in diameter is used as a form. The stick is placed in the center of the circles of filter paper, the smaller inside; the papers are then folded sym- metrically around the stick to form a cup of about

A very little practice enables the operator t o make these evenly and quickly. After being made, they are soaked in benzol t o remove any . grease due t o handling, drained, dried in a steam oven and kept in a desiccator until used.

Besides the apparatus previously described, the laboratory requires beakers, stirring-rods, carbon

2 inches in length.

Apr., 1914 T H E J O URLVAL O F I J V D U S T R I A L A-VD ENGI+VEERIAVG C H E M I S T R Y 28 j

filter tubes, and a weighing bottle, all of which a re regular stock apparatus. A s team oven for drying is desirable, bu t a n ordinary hot air oven can be made to t ake i t s place. X small camel's hair brush or s tou t chicken feather t r immed down to a fan a t t he end, should be available as a policeman for removing the last portions of t h e carbon from beakers. .

A X A LYTIC A L P R 0 C E D U R E

If t a r is t o be assayed, i t must be dried before testing, and after drying i t is passed hot through a th i r ty mesh sieve t o remove any foreign substances. Pitch requires no previous t rea tment , other t h a n the ordinary procedure of insuring a n average sample. If the pitch is hard enough, grinding the material t aken for test will be advantageous in aiding the subsequent solution. I n testing materials of 5 per cent or more carbon content, j grams should be taken for t he test . With lesser percentages, I O grams should be used. The amount is weighed out in a IOO cc. beaker, and digested with about j o cc. of c. P. toluol on t he steam ba th for a period not t o exceed th i r ty minutes. If t he solution is kept hot and constantly stirred, t he diges- t ion can be completed very rapidly. -4 filter cup, prepared as described, is weighed in a weighing bottle a n d placed in a carbon filter tube over a beaker or flask. The toluol-tar mixture is now decanted through the thimble and washed with hot c. P. toluol until clean, using some form of policeman which is un- affected b y toluol for t h e purpose of detaching any carbon which may adhere t o t h e beaker. The cup is finally given a washing with hot C. P. benzol and then, after draining, is covered with a cap of filter paper or a lundum, and placed in the extraction appara tus in which the c. P. benzol is used as a solvent. The extraction is continued until t h e descending benzol is colorless. The thimble is then removed, t he cap taken off, dried in the s team oven, and weighed in the weighing bottle after cooling in the desiccator. The balance used for this work should be accurate t o at least a half milligram. When pitches are being tested, i t is well t o examine the carbon residue for foreign mat te r , such as wood slivers, pieces of bagging, etc. If such foreign mat te r is present, t he test should be rejected. All of t he appara tus for this test , with t h e exception of t h e special water ba th , can be obtained from the Arthur H. Thomas Company of Philadelphia. Pa . This water ba th is only desirable if a number of such tests are run as routine work; for occasional tests i t would not p a y to have one made.

It is t he hope of t he writer t h a t this paper will throw some light on t h e na ture of "free carbon" in t a r products, and t h a t t he procedure given here will be useful t o the chemist who has occasion to test these materials. He would also express his appreciation of t he work of Nessrs. L. B. Shipley a n d C. R. Downs, who performed many of t he tests and analyses which a re recorded in this paper. One thing which must be kept in mind in free carbon tests as in other analyses of this nature, is t h a t t he results obtained are only proximate, and in order t o obtain concordant results, faithful attention to details is necessary. We believe

t h a t we have completely standardized all t h e essential conditions of t he test considered, and t h a t i t can be applied successfully by workers in general.

RESEARCH DEPARTMENT BARRETT ~IANUFACTCRING Co.

N E W Y O R K CITY

THE RELATION BETWEEN THE MELTING POINT AND THE VISCOSITY OF REFINED TARS1

By PHILIP P. SHARPLES

The rough dependence of t h e viscosity of refined t a r s as determined by any of t he s tandard instru- ments and their melting point has been long recognized. N a n y discrepancies have, however, been noted and apparently little thought has been given t o the relation between t h e two in making specifications.

Table I shows a series of samples taken from refined t a r s made on a manufacturing scale from t h e same raw tars. The methods used in analysis a re those described b y S. R. Church in THIS J O U R K A L 3 ( I ~ I I ) , 2 2 7 and 5 (1913)~ 19j.

TABLE I--A S E R I E S O F S A N P L E S O F REFIXED TAR h I A D E FROM S A M E RAW TAR

Viscosity Free Distilla- Engler Float

carbon tion hfelting Schutte 100 cc. a t test Sample Percent- total t o point penetrometer 100' C. at 50' C.

S o . ages 315OC. O F . Sec. a t F. Sec. Sec.

5 1 2 . 1 2 1 . 8 . . . 29 40 94 34 7 1 2 . 0 1 9 . 2 , . , 108 40 127 38 8 1 4 . 0 16.4 . . . 114 50 159 .i 8 9 1 4 . 4 14 9 8 6 . 9 85 60 208 13

10 17.2 1 2 . 7 9 9 . i 90 70 335 110 11 1 8 . 2 10.4 108.7 88 80 43 1 1 i o

- -

The melting point is t he half-inch cube method in water, start ing, however, a t 40" F. instead of 60" F.

The Schutte penetrometer is, strictly speaking, not a penetrometer, b u t a modified melting point. An arbi- t ra ry melting point is assigned and the t ime taken a t t h e assumed melting point t o force out under constant pressure a plug of t he material cooled to 40" F. is noted. The arbitrary melting point is so chosen on a I O " F. scale t h a t t he number of seconds is as near as possible 100.

The float test is t he Xew York Testing Laboratory test . The plug was cooled to 41" F. before floating. The Engler test is made under standard conditions with the exception t h a t IOO cc. were run ofl instead of zoo cc. The reduction of t he number of cubic centimeters with viscous materials allows more concordant results t o be obtained and gives lower figures. X comparison of the three melting points and the

Schutte penetrometer figures show t h a t they advance quite regularly together. Other experiments have shown this same relation t o hold t rue , provided the free carbon content is very nearly the same. Samples 7 and 8 may then be included in our further examination of t h e results without introducing undue error.

An examination of the float test shows an increas- ing interval between samples as we ascend in t h e series. Between 7 a n d 8 t h e interval is 20 sec. while between I O a n d 11 the interval is 60 sec.

The results with the Engler viscosimeter show the 1 Presented a t the Atlanta Meeting of the American Association for

the Advancement of Science, January, 1914.

“free carbon.” its nature and determination in tar products

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