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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E H I S T R Y
Ampola and Rimatori purified their samples of aniline by repeated freezing out of the material. A repetition of their work gave in all cases a freezing C. The only point considerably lower than -6.24' explanation we have t o offer is t h a t their Beckmann thermometer might have been in error. The use of the Beckmiinn thermometer is considered bad practice for accurate work of this kind, since the standardization is difficult and the stem correction excessive. Timmermans' determinations were made on carefully purified aniline, measurements being made by means of a platinum resistance thermometer. We have been able t o check these results fairly well. Jones and Sanderson purified their samples by crystallization, followed by drying and distillation over caustic soda. Temperature measurements were made by means of a mercury thermometer and the freezing point of pure material calculated. We have carefully repeated this work, but failed t o get a freezing point as high as t h a t given in their report. We are a t the present time taking this point up with Professor Jones, hoping t h a t in this way, we may be able t o arrive a t the true results. As a n alternative t o the method of purifying aniline by formation of the oxalate, i t has been found t h a t repeated vacuum distillation gives material of the same freezing point. Samples prepared from recrystallized acetanilide were not of i t high degree of purity. VhLUE OF FREEZING POIKT DETERMINATION
In comparing the chemical analyses and physical constants of a large number of samples of aniline, i t has been noted t h a t the freezing point determination is by far the best criterion of its purity. This method is being used in this laboratory t o determine the purity of commercial samples of aniline. By chemical analysis i t has been shown t h a t the impurities most frequently found in aniline are nitrobenzene, toluidine, and water, these being present in most samples tested in the ratio 2 : 4 : IO. I n order t o have available a short expression for converting the freezing point of a sample directly t o purity, use has been made of t h e plan described by Jones. However, 'it will be noted t h a t t h e figures used are different, due t o the difference in freezing points of the pure samples of aniline upon which the expressions have been based. Jones1 determined the impurities present and assumed a n average molecular weight for them. Substituting this value in the cryoscopic molecular weight formula he obtained a simple expression in which the freezing point may be substituted directly, giving the per cent aniline in the sample. Assuming 82.67 t o be the average molecular weight of the impurities, the following formula may be used: X = 108.79 1.41t, when X = per cent aniline present in the sample, and t = the observed freezing point in O C. I n developing this formula i t was necessary t o accept the cryoscopic constant of Ampola (5870). Should this be slightly in error, t h e discrepancy in the
+
1
J . SOC.Chem. I n d . , 39 (1920), 81
883
result will be practically negligible. This is also the case when the relation of impurities is altered. SUMMARY
I-It is believed t h a t the following are the true physical constants of aniline: Freezing point.. . . . . . . . . . . . . -6.24' C. Boiling point.. . . , . . . . . . . . . . 184.32", 184.39' C. at 760 mm. Specific gravity (15°/150 C . ) Refractive index (20' C.) . . .
.
1.0268 1.5850
a-The indications are t h a t the freezing point is the best criterion of t h e purity of aniline. 3-In order t o calculate the purity of a sample of aniline from its freezing point, use should be made of the formula: X = 108.79 1.41t.
+
THE DETECTION AND ESTIMATION OF YELLOW AB AND YELLOW OB IN MIXTURES' By Walter E. Mathewson BUREAU O F CHSMISTRY,
u. s. DEPARTMENT OF
D c. Received July 15, 1920
AGRICULTURE, WASH-
INGTON,
The dyes benzeneazo-@-naphthylamine(Yellow AB) and o-tolueneazo-@-naphthylamine (Yellow OB) are a t present the only oil-soluble coal-tar colors t h a t may be used in food products without objection by the U. S. Department of Agriculture, and for this reason properties t h a t can be applied t o the chemical examination of mixtures containing them are of some special interest. Cornelison2 and Lubs3 have described methods for separating them from colored fats and oils and identifying them. PREVIOUS INVESTIGATIONS
Several years ago the writer carried out some experiments with these dyes in connection with the study of general methods4 of color analysis. Attempts t o separate them from colored salad oils by diluting the products with 2 t o 4 volumes of gasoline and shaking out with a mixture of phosphoric and sulfuric acids gave unsatisfactory results, especially in the case of Yellow OB, for although the dye was removed quite readily from the oil-gasoline solutibn a large proportion of it, usually 5 0 per cent or more, was destroyed in t h e process. The behavior of the dyes in other acid mixtures, as for example, ether and hydrochloric acid, was also somewhat peculiar. The coloring matter was apparently very slowly extracted from ether by shaking with 5 N hydrochloric acid, forming a red solution in the acid t h a t gradually faded, so t h a t on standing over night both layers became colorless. As compounds of this class are known t o exist in several different forms, it was supposed t h a t the form more readily extracted was not present in any considerable amount in the organic solvent solutions and was produced rather slowly under t h e influence of the dilute acids used. At the time these tests were made Yellow AB and Yellow OB apparently were not being used in food products and were said t o be off the 1 1
8 4
Published by permission of the Secretary of Agriculture, J . A m . Chem. SOC.,80 (1908), 1478. THIS JOURNAL, 10 (1918), 436. U. S. Dept. of Agriculture, Bulletin 448.
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market, so no further attention was given t o the matter. Lubsl found later t h a t practically no Yellow OB was extracted from 0 . 0 0 2 per cent solutions in gasoline by shaking with 4 t o 6 N hydrochloric acid. H. A. Lubs and A. B. Clark2 also measured spectrophotometrically the rate of decomposition of Yellow OB in a mixture made by diluting 2 cc. of 0.4 per cent alcoholic solution of the dye t o I O O cc. with a solvent prepared from g o cc. glacial acetic acid, I O cc. water and I O cc. concentrated sulfuric acid. The loss observed in t h e first half hour was about 2 per cent, in the first 5 hrs. about 1 5 per cent, and in t h e first 7 5 hrs. about 6 7 per cent. The dyes are quite reactive substances, and it seemed not improbable t h a t t h e results obtained in the first experiments had been influenced by impurities in the reagents, the presence of oxides of nitrogen in t h e phosphoric acid, and aldehydes in the ether being suspected in p a r t i ~ u l a r . ~The test with j N acid and ether has been repeated with reagents now in stock, and the slow passage of the coloring matter into t h e acid layer and its subsequent disappearance noted exactly as before (the acid used was made by diluting ordinary C. P. acid, while the ether was of U. S. P. grade). I n view of t h e results obtained with gasoline and described below, i t was not thought necessary to make further study of the ether mixtures. The solutions commonly used for tests of this kind are very dilute so t h a t quite minute quantities of reactive impurities in the reagents are sufficient t o alter a large proportion of the coloring matter. EXPERIMENTAL PART
The experiments discussed in the present paper were made mainly t o form a basis for quantitative methods. It was found t h a t light (“low b. p.”) gasoline and dilute sulfuric acid in concentrations ranging from 3 t o 2 5 N gave a set of solvents fairly satisfactory for work with these dyes and which, although somewhat unpleasant to use, were not worse in this respect than any others t h a t could be selected. I n order t o remove any traces of nitrous acid or free halogens from t h e acid, t h e mixtures were treated with hydrazine sulfate in the proportion of I g. per liter, most of the salt crystallizing out again on standing. The specific gravity of the mixtures corresponded almost exactly with those of pure dilute acid of t h e sgme concentration. When solutions of Yellow AB in commercial lowboiling gasoline were shaken with dilute sulfuric acid of such concentration as t o extract a part of the dye, some of the latter was changed into a n orange substance which was relatively much more soluble in the acid layer than the dye itself. It could be separated by diluting the acid solution with half its volume of water, removing unchanged, dye with gasoline, neutralizing, and extracting with ether. The gasoline used for the tests was purified in two liter lots by treating with 0.5 to 1.0 g. Yellow AB, then shaking out with four or five 2 0 0 cc. portions of concentrated sulfuric acid, the liquids being allowed to stand together for some time. A glass-stoppered bottle was used for the mixing, the 1 2
cit. THISJOURNAL, 10 (1918), 438. LOG.
Krauch, “Die pp 8 and 310. 8
Prufung der
Chemischen Reagentien,” 3rd Ed.,
Vol.
12,
NO.9
wash acid being removed or blown out with a washbottle fitting. With this purified gasoline very little or none of the orange product just mentioned was 200 c formed. The specific gravity of this gasoline (=.) was 0.6460,and when heated on the water bath, about 7 0 per cent distilled between 38’ and 5 5 ’ C. RESULTS W I T H V A R I O U S DYES-when gasoline SOlutions of Yellow AB containing about 0.005 g . dye per I O O cc. are shaken with dilute sulfuric acid, little or none of the coloring matter passes into the acid solvent unless its acidity is above 7 N ( 3 . 5 moles per liter). With acid 16 N or stronger (to 2 5 N ) practically all dye is removed from the gasoline. Yellow OB shows similar behavior, but is relatively somewhat more soluble in t h e gasoline so t h a t the acid concentrations corresponding t o the limits just given are about I O and 18 N . The other common oil-soluble dyes are quite different in relative solubility, aminoazobenzene (Aniline Yellow), aminoazo-a-toluene and dimethylaminoazobenzene (Butter Yellow) passing in chief proportion into the acid when this is 7 N or stronger, while benzeneazo-&naphthol (Sudan I), m-xyleneazo@-naphthol (Sudan 11), benzeneazo-benzeneazo-Pnaphthol (Sudan 111)) and a-naphthaleneaxo-pnaphthol (Carminaph Garnet) remain in chief quantity in the gasoline when t h e acid concentration is not greater than 18 N . The variation in relative solubility with acid concentration is not so marked with benzeneazophenol, benzeneazoresorcinol (Sudan G) and a-naphthaleneaso-a-naphthol (Sudan Brown), b u t t h e first two in gasoline and 7 N acid mixtures appear t o go in larger proportion into t h e acid. N o tests were made with good preparations of these three dyes and the commercial products available were very impure. However, these coloring matters, because of their re- ‘ active phenolic character, will ordinarily be separated most conveniently from t h e P-naphthol and amino derivatives first named by t h e use of alkaline solvents. Benzeneazo-a-naphthylamine and aminoazo-anaphthalene are removed from gasoline by 7 N acid, but a large proportion of t h e dye is precipitated, as i t appears t h a t the salts formed are not soluble in acid of this Concentration. #-Tolueneazo-P-naphthylamine behaves similarly t o Yellow OB, as might be expected, and m-xyleneazo-P-naphthylamine differs from Yellow O B about as t h a t dye differs from Yellow AB. All of the dyes are removed almost completely from gasoline solution by shaking with 24 t o 2 j N sulfuric acid. Benzeneazo-a-naphthol, bixin, and curcumin are practically insoluble in gasoline, so t h a t they could not be tested directly. TESTS FOR Y E L L O W A B A N D Y E L L O W oB-The difference in solubility of Yellow AB and Yellow O B from most of the other dyes has occasionally been applied as a convenient test for the latter in mixtures. A gasoline solution is prepared containing about 0.00j g. dye per I O O cc., and 3 0 cc. are shaken out first with I or 2 cc. portions of 7 N sulfuric acid, then with two portions of 18 N acid, and finally, if t h e gasoline still contains color, with 24 N acid.l A trace of Yellow 1 The solvents must be vigorously shaken together for at least half a minute. If the 7 N acid extract is reddish it may be shaken with an equal volume of gasoline to remove Yellow AB.
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~ 9 2 0
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
A B may come out with the 7 N acid, but the 18 N acid will contain practically all of the coloring matter when only Yellow AB and Yellow OB are present. Carrotin and some of the coloring matters found in annatto seem t o remain chiefly in the gasoline even after the shaking with 2 4 N acid, though bixin is taken out by acid of this concentration. The ordinary liquid mixtures sold as food colors consist of 2 t o 3 per cent solutions of the dyes in oil and have been tested directly after diluting with from joo t o 1000 parts by volume of gasoline. If the amount or concentration of dye in a mixture under examination is quite unknown, it can be fixed closely enough by matching against a standard made by dissolving 0 . O o j g. of Yellow AB in 100 cc. gasoline. The acid used for qualitative tests has not usually been treated with hydrazine sulfate, or carefully standardized, being made by diluting measured amounts of the concentrated C. P. acid, which is about 3 j N , cooling, and bringing t o definite volume. Unpurified low-boiling gasoline gave fairly satisfactory results for such tests. Q U A N T I T A T I V E SEPARATION-The differences in relative solubility of the different dyes are not great enough in many cases t o permit a quantitative separation being made by a single shaking-out operation. Experiments were made with Yellow AB, Yellow OB, Butter Yellow and Sudan I t o learn their behavior when subjected t o a systematic fractionation procedure, the conditions being fixed with especial regard t o the separation of Yellow AB and Yellow OB from each other and from other dyes. A solution of 0.00400 g. dye in 40 cc. of gasoline was washed or shaken out with four 2 0 cc. portions of the dilute acid. Two additional separatory funnels containing 40 cc. portions of gasoline were provided and each acid washing portion, after being drawn out of the first separatory funnel, was shaken out successively in t h e second and third funnels. A fifth additional 2 0 cc. portion of acid was shaken in the second and third funnels and finally a sixth portion in the third. The gasoline extracts were combined, washed by shaking with water, then with a dilute solution of sodium acetate and acetic acid, and finally again with water. The gasoline was driven off on the steam bath, care being taken t o avoid volatilization of the dye, and the residue dissolved in 93 per cent alcohol. The alcoholic solution was diluted t o exactly I O O cc. (or t o 2 5 cc. when i t was not strongly colored), the light absorption constant a t 0 . 4 3 6 ~ determined and the amount of dye calculated, using the figures for extinction coefficients given in the latter part of this paper, The acid portions or washings were combined, diluted with an equal volume of water, the dye extracted by shaking with two portions of gasoline, and the gasoline solution thus obtained treated in the same manner as the one first described. The dilute acids were saturated with hydrazine sulfate as stated and are designated as I O , 13, and 16 N , the exact strengths as determined by titration being 10.17, 13.01, and 15.95. The specific gravities E ( 2 0 0 c,) by pycnometer were, respectively, 1.291j, 1.3637, and 1.4370.
Tests were made by the procedure first described, using 13 N acid and Yellow AB. Four and eighttenths per cent of the dye was recovered from the gasoline, 92.2 per cent from the acid. With Yellow OB under similar conditions 83.5 per cent was recovered from the gasoline, 10.1 per cent from the acid. I n experiments made with 16 N acid the procedure was modified by omitting the use of a third funnel. Four portions of acid were passed through the first and second funnels and a fifth portion through the second. The figures obtained under these conditions with Sudan I corresponded t o a recovery of 0.4 per cent from the acid, and I O O per cent from the gasoline. The parallel test with Yellow OB showed t h a t but 1.0 per cent of the dye remained in the gasoline. The amount in the acid was not estimated carefully, but a colorimetric comparison indicated go per cent or more of the amount originally taken. When I O N acid was used the original procedure was modified by omitting the last three washings or acid portions. An experiment with Butter Yellow showed t h a t under such conditions but 0 . 5 per cent remained in the gasoline. The dye in the acid was estimated roughly by colorimetric comparison and appeared t o correspond t o practically the amount originally taken. A similar test with Yellow AB showed the acid washings t o contain but 0.9 per cent of the dye taken. (When the funnels were washed according t o the original procedure 4.0 per cent of the dye was found in the acid.) The experiments show t h a t Yellow AB and Yellow OB can be separated by means of dilute sulfuric acid and gasoline from Butter Yellow and Sudan I and presumably from most other common oil-soluble dyes t o a degree meeting the requirements of ordinary quantitative work. The optical data for the total mixture are readily obtained, so t h a t the amount of Yellow AB or Yellow OB (or the sum of the two when both are present) may be determined by difference. I n fractionating a mixture of two dyes in which one is present in relatively small proportion, the conditions can be shifted rati-onally t o give more accurate results, for example, by using a larger number of portions of the solvent in which the predominating dye is more soluble. Although the distribution ratios vary more or less with concentration, and usually t o a degree t h a t make such analytical processes unmanageable with colorless substances, the course of the separation is apparent t o the eye in the case of dyes. The fractionation methods for this reason possess a reliability and flexibility with dyes t h a t they quite lack with other compounds. When making separations with dilute sulfuric acid, special care has always been taken t o see t h a t the stoppers and stopcocks of the funnels were 'seated firmly before making the shakings, and t h e funnels have been held a t the top neck, the latter being covered with a filter paper cap t o protect the hand. Butter Yellow and the other dyes more readily soluble in aqueous liquids can, however, be fractionated as satisfactorily with less corrosive solvents. A mixture of Sudan I and Butter Yellow (at one time in common use) is separated in this laboratory with 4 -Vhydrochloric acid
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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
and ether (using two portions of each of t h e solvents). A satisfactory quantitative separation of mixtures of Yellow AB with Yellow O B cannot be made with r 3 N sulfuric acid unless a more elaborate procedure is followed than t h a t described. The method considered best for such mixtures consists in caTrying through a fractionation (usually with two or three funnels) choosing such conditions t h a t practically all of one of the dyes will be removed from either the gasoline or the acid. The amount of the pure color remaining is determined and a correction made by comparing with t h e results obtained with known solutions or mixtures carried through in t h e same way. The quantitative separation of these dyes from dilute oil solutions, such as colored oleomargarine or salad oil, has not been carefully studied, but it is believed t h a t a simple adaptation of the qualitative method of diluting the oil with a few volumes of gasoline and extracting with a strongly acid solvent gives very unreliable results. E S T I M A T I O N O F DYES-The dyes have been estimated in all cases by means of the spectrophotometer’ after the removal of interfering substances. A KonigMartens instrument was used but, instead of the absorption cell with glass cube 6r Schulz body employed for work described in a preceding paper,2 a double cell was used, oae compartment being filled with the solutiofi under examination, the other with the pure solvent. This cell consisted of three plane parallel glass plates held together by two U-shaped pieces of steel serving as clamps. The middle plate was exactly I cm. in thickness and contained two circular holes a t the middle, forming the cavities. These cavities were 2 cm. in diameter and 0.2 cm. apart and were filled b y means of small vents 0.5 cm. in diameter drilled through one of the edges of the plate. This cell gave no trouble because of leakage, was easily cleaned, and furnished results requiring no correction for absorption, reflection, and refraction of t h e glass and solvent. A similar cell was also tried in which the middle plate was of brass and channeled near the edges so that a stream of water a t constant temperature could be passed through it. Such a plate would also give less error from scattering light, but the one tried tely finished, and could not be made tight. The glass cell was held in a heavy brass carrier and adjusted to insure the full and symmetrical illumination of the slits of t h e spectrophotometer. A quartz. mercury lamp was used as a light source, t h e instrument being set to show the blue line 0 . 4 3 6 ~ . The specific absorption for light of this wave length is very hilgh with dyes examined, though the peaks of their absorption curves are somewhat further toward t h e grken in most cases3 1 A full discussion of the development and use of spectrophotometric methods of analysis is given in the handbook by G and H. Kruess, “Kolorimetrie und Quantitativ Spektral-Analyse,” Hambiirg, 1909. * J . Assoc. Of. Agr. Ckem.. 2 (1916), 164. 8 The extinction coefficient found for Sudan I (0.002 g. per 100 cc.) in absolute alcohol in white (arc) light, 0 . 4 7 3 ~to 0.480#, was 1.18, a value about 40 per cent higher than that given at 0 . 4 3 6 ~ under the conditions described in this paper. With the other dyes the differences were mUQhless.
Vol.
12,
No. g
Solutions of purified preparations of the dyes in alcohol of specific gravity (%:) 0.8055 (93.0 per cent by weight), containing 0.002 g. per I O O cc., gave values for the extinction coefficients as shown i n t h e table. DYE
EXTINCTION
COEFFICIENT
...................... .................. . .................. ........................... .
Butter Yellow.. Yellow A B . . Yellow O R . , Sudan I...
1.86 1.12 1.09 0.86
The figures calculated from measurements made with solutions containing 0.001 g. per I O O cc. in t h e case of Butter Yellow, and 0.004 g. per 100 cc. in the case of the others, indicated t h a t t h e absorptions may be assumed t o be proportional t o the concentrations within the ranges in which they may be accurately measured by the apparatus employed. The measurements were made a t 2 3 ’ C. Readings made a t higher and lower temperatures showed t h a t a variation of 3’ affected the reading less than I per cent. Except with Butter Yellow, t h e effect appeared t o be negligible. The effect of variations in the strength of the alcohol used as solvent was also determined. Fortunately the absorption at 0 . 4 3 6 ~does not vary greatly with changes in t h e water concentration in case of Yellow AB and Yellow OB and may be considered as practically constant with alcohol ranging from 90 t o 95 per cent by weight. The effect of water in the solvent is more marked with the other two dyes, t h e solutions being redder and the absorption lower a t 0 , 4 3 6 ~ with increasing water content. The ordinary method of calculating t h e amounts of each of the components of a known binary mixture of dyes from the extinction coefficients determined a t two points in the spectrum has been tried for t h e analysis of miartures of Yellow AB and Yellow OB. The absorption curves of these substances are so similar in form and position, however, that the method gives very inaccurate results unless the measurements are made with unusu;ll care. The extinction coeffis of 0 . 0 2 g. per liter a t 0 . 4 9 2 ~ cients for concentrat are approximately 0.66 for Yellow AB and 0.74 for Yellow OB. Measurements made in the spectral region at or near 0 . 4 9 2 ~ are suitable for use in connection with those taken at a . 4 3 6 ~ )but as no source of strong monochromatic light was available for making such measurements.it has been necessary t o employ a white light source (Mazda lamp) and to avoid t h e difficulties arising fr6m the use of non-homogeneous light by carrying through standard solutions or mixtures a t the same time. I n some cases these standard solutions were used instead of the pure solvent in the comparison cavity of the double cell. The relative, difference in the specific absorption of the two dyes appears t o be considerably greater a t 0 . 5 4 6 ~ (the strong green line of the mercury arc) than in the blue and violet regions of t h e spectrum. Measurements made a t this point, using solutions in 93 per cent alcohol containing 1.00 g. per liter of t h e preparations already mentioned, gave values of 1.0j and 1.53 for Yellow AB and Yellow O B , respectively.
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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
Such data can scarcely be applied t o the estimation of the dyes because of the relatively great effect of colored impurities on the absorption constants in the regions where the transmission is high. With commercial samples, the absorption a t 0.546~has been considered of some value as a n index t o their grade. Sudan I and Butter Yellow can be more readily determined spectrophotometrically when in admixture with each other or with one of the dyes just discussed, the extinction coefficients in concentrations of 0 . 0 2 g. per liter a t 0.492~being approximately 1.17 for Sudan I and 0.26for Butter Yellow. Butter Yellow has also t h e convenient property of becoming red (giving high absorption a t 0.546~) with small amounts of strong acids. However, these dyes may be readily separated and estimated directly, and this procedure has been preferred. Although t h e wave length of the blue light for which Yellow AB and Yellow OB show equal absorption is slightly greater t h a n 0.436p, t h a t of the mercury line, the extinction coefficients are so nearly t h e same for this radiation t h a t t h e mean of their values may be used for calculating the sum of the two dyes in a mixture free from other coloring matters without introducing an error exceeding one-seventieth of the value found.
887
use of acid immiscible-solvent mixtures for separating oil-soluble food colors. 11-A description is given of the use of light gasoline and dilute sulfuric acid of different' concentrations for detecting foreign dyes in commercial Yellow AB and Yellow OB colors. 111-Experiments are described indicating methods for the quantitative separation of mixtures of t h e dyes. IV-Spectrophotometric data are given which have been applied t o the quantitative estimation of Yellow AB, Yellow OB, Butter Yellow, and Sudan I. DETERMINATION OF SULFUR FORMS IN COAL132 By Alfred R. Powell PITTSBURGH EXPERIMFNT STATION,BUREAUOF MINES, PITTSBURGH, PA.
An accurate method for determiniqg each form of sulfur in coal would be useful, as indicating how much of the sulfur-containing material could be removed from the coal by washing processes, what effect the sulfur had on the heating value of the eoal, how the various sulfur forms behaved during the coking and gas making processes, and other facts of interest t o coal technologists. HISTORICAL
Iron pyrite has been known for a great many years as one of the constituents of coal, and there has also been I n conclusion, a few properties which have been applied as color tests for the dyes may be mentioned. fairly good evidence of the presence of sulfur in orYellow AB and Yellow OB readily condense with formal- ganic combination. The first method proposed for dehyde in presence of strong acids or acetic anhydride, the determination of these two forms was by means of sodium h y p ~ b r o m i t e . ~The supposition was t h a t t h e Yellow A B mixtures being much redder in shade.' the hypobromite dissolved the pyrite and sulfates Five cc. of a gasoline solution containing 0.001 g. dye per IOO cc. may be shaken in a test tube with 5 cc. of a without affecting the organic sulfur, but i t was later mixture of I part commercial 40 per cent formaldehyde shown4 t h a t some of the organic sulfur was brought into solution and 4 parts acetic anhydride. The coloring solution by this method. I n a method used in recent years the total iron in matters are extracted by t h e anhydride, Yellow AB and p-tolueneazo-@-naphthylamine forming solutions t h a t the coal, minus any water-soluble iron t h a t may be become red in a few seconds. Yellow OB and llz- present, is considered t o be combined as pyrite. From xyleneaz,o-@-naphthylaminegive orange solutions under this value is calculated the sulfur existing as pyrite. Any sulfur present as sulfate may be determined by the same conditions. Yellow AB and Yellow OB form in fuming sulfuric a simple extraction with dilute acid. The pyritic acid (about 2 0 per cent sulfur trioxide) violet-blue sulfur plus the sulfate sulfur when subtracted from solutions which slowly become red on standing. the total sulfur gives t h a t organically combined, prop-Tolueneazo-&naphthylamine and m-xyleneazo-@- vided no other form exists in the coal. This method naphthylamine dissolve with a red color. Solutions in must be regarded as a rough approximation only, acetic anhydride containing 0.01 t o 0.001 per cent of since i t disregards the presence of iron silicate. A method based on a gravity separation was devised any of these four dyes become bluish red on the addiin 1914by M-essrs. A. C. Fieldner and F. D. Osgood, tion of a few drops (or 0.02 volume) of concentrated sulfuric acid, changing in 2 or 3 min. t o a clear yellow. of the Bureau of Mines. The coal was separated into float and sink fractions by the use of zinc chloride SUMMARY solution of 1.35 specific gravity. The sulfur in the I-Attention is called t o a source of error in the heavy portion was considered as pyrite and t h a t in 1 Goldschmidt and Poltzer, B e y . , 24 (1891), 1000, condensed benzenethe light fraction organic sulfur, after calculating the azo-&nhphthylamine by heating with formaldehyde at 140' C , forming small amount of iron in this latter fraction t o pyrite. phenyldihydro-8-naphthotriazine. With acetaldehyde the reactlon began at ordinary temperature on mixing the substances. I t has been observed This method was somewhat approximate, but its here that the reaction between formaldehyde and Yellow AB (or Yellow application indicated t h a t organic sulfur was present OB) takes place very readily when a concentrated alcoholic solution of the in most coals t o a much larger extent t h a n had been substance is treated with sufficient hydrochloric acid to form the salt of the dye base. The colorless triazine derivative forms the chief reaction product generally supposed. COLOR TESTS FOR YELLOW AB A N D YELLOW O B
under these conditions and is readily separated from the mixture. If a 0.002 per cent solution of Yellow AB in ordinary 9.5 per cent alcohol is treated with one-fourth its volume of concentrated hydrochloric acid or 18 N sulfuric acid, and neutralized, it will be found that the hue of the mixture does not return t o yellow but remains orange-red, most of the dye having undergone condensation with substances present in the solvent.
Published by permission of the Director of the U. S Bureau of Mines. Presented at, the 59th Meeting of the American Chemical Society, St. Louis, Mo., April 12 to 16, 1920. 8 T. M . Drown, Cltem. News, 43 ( l 8 8 l ) , 89. 6 Ferd. Fischer, 2. angew. Chem., 12 (1&99),764. 1 2
