Sept., r 9 2 o
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
t o 11.5 points; after dryingit tested 1 1 . 6 points. These figures obviously represent poor extraction, and considerable loss of strength in t h e evaporator, b u t show no loss from bacterial action in drying. Jelly strength tests made on samples direct and after incubation for 24 hrs. a t 37' C. show little or no loss in strength of nearly sterile gelatins, while those in active state of decomposition show considerable loss with t h e development of bad odors. The following results illustrate this : 35' C. 3 G . per 100 Cc. l... . . . -20.3 2 ....... -20.5 3.. . . . . -20.3
No.
Rot. at 15' C. Rot. at 15' C. before after Incubation Evaporation -33.4 -33.8 -36.8 -39.7 -31.6 -35.6
JELLY
STRENGTH
MEASUREMENTS
BY
A
reduction of pressure is produced (6 dm. of water), which causes a depression in t h e jelly which can be measured by a micrometer depth gage reading t o thousandths of a n inch. Some results are given in Table 111. TABLE111-MECXANICAL TWTS AT 10' C. Displacement in Inches Rotation Sample by Partial Vacuum Increme-it No. 6 Dm. Water 100 c. 393.. . . . . . . . . . . . . . . . . 0.137 25.7 25.6 168 .................. 0.135 20.0 407 .................. 0.269 23.5 859 .................. 0.218 1 .................. 0.136 25.1 7 . . . . . . . . . . . . . . . . . . 0.151 24.5 24.0 169... . . . . . . . . . . . . . . . 0.220
Odcr after Evaporation Sweet Bad Bad
The solutions were filtered through magnesium carbonate t o clarify. The increase in rotation in No. I was probably due t o evaporation and experimental error. The loss of jelly strength in Nos. 2 and 3 was quite pronounced, with corresponding production of disagreeable odors. A progressive increase in levorotation (or mutarotation) obtained from a solution cooled quickly below 3 j" C., accompanied by t h e production of a jelly after a change of approximately 4.7 ' V., is very positive proof of t h e presence of gelatin in any solution concentrated enough t o jelly. MECHANICAL
TESTER
Several different mechanical testers have been developed in t h e laboratory but only one, which recommends itself as accurate and requiring a small amount of sample, is here described. The bubble test is accurate t o about 3 per cent on high strength gelatins comparing quantities which just produce t h e standard jelly. We have seen t h a t t h e minimum amounts necessary for jelly production change in a definite way following t h e mutarotation. I t was thought desirable t o make certain t h a t similar relations existed in much higher concentrations. Fig. I represents an 80 mm. glass funnel with short stem accurately formed t o a 60' angle. Mercury weighing 1 2 0 g. is poured into t h e funnel closed at t h e end. The diameter a t t h e surface of t h e mercury is 3 cm. Fifty cc. of t h e gelatin solution are poured over t h e mercury and allowed t o solidify in a horizontal position (determined by spirit level) i n a constant temperature bath a t 10' C. We have now formed S u c t i o n + Manometer a definite sized reFIG. 1 producible jelly in t h e shape of t h e frustrum of a cone. When t h e jelly is t o be tested t h e mercury is allowed t o run out and t h e jelly is connected with a water manometer, and a definite
881
SOME PHYSICAL CONSTANTS OF PURE ANILINE' By C. L. Knowles EASTERN LABORATORY, E. I.
DU
PONTDE NEMOURS & Co., CHESTER, PA.
The importance of aniline t o t h e dye industry has long been recognized, b u t no practical method of analysis has been available for general use in judging its quality. An attempt has therefore been made t o find a method of analysis or test which would not only be accurate, but of such a nature t h a t i t could be applied quickly and easily in t h e control of t h e manufacture of this product. A survey of chemical methods of analysis disclosed t h e fact t h a t , due t o t h e rather large experimental errors, most of them fail when t h e purity of t h e aniline exceeds 99. j per cent. Attention was therefore turned t o t h e possibilities of t h e application of t h e physical constants for accurately judging t h e purity. It would naturally be expected t h a t t h e physical constants of such a common intermediate would long since have been established beyond any reasonable question. As a matter of fact, a great number of investigators have made a study of aniline but, instead of establishing these points, widely diverging results have been published. On consulting t h e literature, no less t h a n 1 6 different values for t h e freezing point of aniline were found. These varied between -8' and -5.96 ' C. , whilg values for the boiling point ranged from 182.5' t o 184.8' C. Of t h e gumerous results given, t h e on$ ones considered were those in which t h e method of purification and methods of recording temperatures were fully described. The following have been chosen as most reliable, and are those generally accepted : Ampola's freezing point of - j . g 6 " , Timmermans' of - 6 . 2 0 ' ~ and t h a t of Jones and Sanderson of -6.00' C. The latter has been published since t h e completion of this work, along with a formula for determining the purity of aniline from its freezing point. Timmermans, Callender, and Beckman apparently give the most accurate boiling points, their results being 184.40 O , 1 8 4 . 1 0and ~ ~ 184.30' C. Since no conclusions could be drawn from these results, i t was necessary t o prepare a sample of pure aniline, and t o determine accurately its physical constants. In t h e course of this work i t was soon discovered why so many different values had appeared for t h e physical constants of aniline, since t o purify
L +
1 Presented at the 59th Meeting of the American Chemical Society, St. Louis, Mo., April 12 t o 16, 1920.
88 2
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
Vol.
12,
aniline and maintain it in a pure state was found t o be a matter of considerable difficulty.
No. 9
beyond t h e scope of this paper. It has been noted t h a t t h e purer t h e sample of aniline t h e more stable i t is toward air and light. Our purest samples have P R E P A R A T I O N O F THE SAMPLE Two liters of colorless aniline were distilled v a c u o darkened but slightly when kept in diffused light for four times, rejecting t h e first and last portions in each monthscase. The product thus obtained was allowed to EFFECT O F MoIsTURE-one Property of aniline which drop slowly into a saturated solution of recrystallized caused considerable trouble in our work, .and which oxalic acid. The aniline oxalate was filtered off, apparently has received but very little attention in t h e washed several times with water, and three times re- Past, is its extreme hygroscopicity. It is believed t h a t crystallized from $ 5 per cent ethyl alcohol. The salt this alone accounts t o a large extent for the conflicting was washed with pure ethyl ether after each crystal- results found in t h e literature. If aniline in t h e pure lization. I n order t o regenerate t h e aniline, a satu- state be exposed t o the air for'but one hour, t h e freezrated solution of recrystallized sodium carbonate was ing Point and boiling Point are materially affected; added, the aniline distilled off, and distilled in vacuo consequently extreme Care must be taken in determinthree times, When possible, determinations ing constants Of the pure material. If undue time is were made immediately on the sample. When this required for these determinations, no accurate figures could not be done, t h e material was kept in a darkened can be obtained. For this reason all samples were freshly distilled in v a c u o , and determinations made as vacuum desiccator. rapidly as possible. I n order t o check these results, DETERMINATION O F PHYSICAL CONSTANTS attempts were made t o determine freezing points im BOILING PoI"r-For t h e boiling-point determination vacuo, but due to the mechanical ena standard apparatus was countered, no results of value were obtained. Results used, readings being taken by Of a platof both freezing-point and boiling-point determinainum resistance thermometer. This apparatus tions made in an atmosphere of dry inert gas, such as had been recently standardized by the u*s. Bureau of nitrogen or carbon dioxide, were identical with those Standards for three Points: for ice7 the boiling of determinations made rapidly in the presence of air, point Of The point Of water, and the I n order t o clearly demonstrate t h e effect of moisture manufacturers guaranteed an accuracy of 0.01~. on t h e purity of aniline, freezing points were made Before and after each determination the thermometer hourly on a sample exposed to the air. The initial was further checked against t h e ice point and freezing freezing point was --6.350 c,; after I hr. it had fallen point of benzene. It is of interest t o note t h a t we were to -6,600 c.; after I6 hrs, it was.7.300 c,;and after able t o check very well t h e freezing point of benzene, 46 hrs. a freezing point of -8.200 c. was obtained. obtaining 5*4860 '*, as 'Ompared with 5.493' *' * Assuming the formula for water a t 0' C. t o be (Hz0)4,1 0.007 as obtained by Richards.' this represents 2.4 per cent water absorbed; based Following all precautions mentioned later, we ob- on t h e molecular weight of water as 18, t h e amount of tained consistently a boiling point of pure aniline of water present becomes o.6 per cent. 1 8 4 . 3 2 ~t o 184.39' C. a t 760 mm. pressure. The effect of entrained air and diminished pressure FREEZING POINT-Immediately after vacuum distilla- on freezing points has been carefully studied by tion, the pure (Io to ' 5 was transferred Richards.2 He concludes t h a t t h e error due t o vacuum to a test tube surrounded by a larger tube, and is practically negligible, as is also t h a t due t o dissolved supported a t the top by a thin ring of asbestos. The air in t h e of benzene. platinum resistance thermometer and a stirrer were DISCUSSION O F RESULTS inserted, and t h e whole immersed in a brine mixture The following have been chosen as t h e most reliable ~h~ sample was stirred at a to - 1 2 0 at of Previous freezing-point determinations: uniform rate and t h e freezing point determined. It Freezing Point was found t o be -6.24' C., consistent checks being YEAR c. obtained. Ampola and Rimatori., .............. 1897 -5.961 SPECIFIC GRAVITY-Specific gravity determinations Timmermans. ...................... 1911 --6,20* were made on t h e freshly distilled sample in a Jones and Sanderson.. ............... 1920 -6 .OOa 1 Garz. chim. ital., [ l ] 27, 35. pycqometer a t 15' C., and compared with water at 2 Bull. SOC. chim. belg., 26 (1911),300. t h e same temperature, giving a value of 1.0268 a t a J . sot. Chem. Ind., 89 (I~zo), 87. I 5 '/I 5 ' c. For boiling points t h e following appear fairly reREFRACTIVE INDEX-The index of refraction was liable: determined by means of an Abbe refractometer, Boiling Point manufactured and calibrated by the Zeiss Instrument YEAR 0 c. Co. The best samples of aniline had an index of Callender., ......................... 1899 184.10' refraction of 1.5850 a t 20' C. Timmermans ....................... 19 1 1 184.402
c,
P R E C A U T I O N S OBSERVED
Numerous articles have been published in reference t o t h e effect of air and light on aniline. While this phase of t h e subject is of great interest, it is manifestly 13.
Am. Chrm. Soc., 41 (1919),2019
..........................
1
Beckmann Phil. Mag., 151 48 (1899), 519.
* Bull. soc
chim. balg., 26 (1911).
300.
* 2. physik. Chem., 89 (1914),112.
,z. physik. Chem., i2 (1893),433. 9 LOC.
cit.
1914
184.303
Sept., rg2o
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 a n d Rimatori purified their samples of aniline by repeated freezing out of t h e material. A repetition of their work gave in all cases a freezing point considerably lower t h a n -6.24' C. The only 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 t h e 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 t h e 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 t h e t r u e results. As a n alternative t o t h e method of purifying aniline by formation of the oxalate, i t has been found t h a t repeated vacuum distillation gives material of t h e same freezing point. Samples prepared from recrystallized acetanilide were not of i t high degree of purity. VhLUE OF FREEZING POIKT DETERMINATION
In comparing t h e chemical analyses and physical constants of a large number of samples of aniline, i t has been noted t h a t t h e freezing point determination is by far t h e best criterion of its purity. This method is being used in this laboratory t o determine t h e 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 t h e 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 t h e 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 t h e freezing point may be substituted directly, giving the per cent aniline in t h e sample. Assuming 82.67 t o be t h e average molecular weight of the impurities, t h e following formula may be used: X = 108.79 1.41t,
+
when X = per cent aniline present in t h e sample, and t = the observed freezing point in O C. I n developing this formula i t was necessary t o accept t h e cryoscopic constant of Ampola (5870). Should this be slightly in error, t h e discrepancy in t h e 1
J . SOC.Chem. I n d . , 39 (1920), 81
883
result will be practically negligible. This is also t h e case when the relation of impurities is altered. SUMMARY
I-It is believed t h a t t h e following are t h e t r u e 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 t h e freezing point is t h e 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 t h e 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 t h e 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, a n d for this reason properties t h a t can be applied t o t h e 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 t h e writer carried out some experiments with these dyes in connection with t h e study of general methods4 of color analysis. Attempts t o separate them from colored salad oils by diluting t h e 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 t h e case of Yellow OB, for although the dye was removed quite readily from t h e 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. T h e coloring matter was apparently very slowly extracted from ether by shaking with 5 N hydrochloric acid, forming a red solution in t h e 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 t h e form more readily extracted was not present in any considerable amount in t h e organic solvent solutions a n d was produced rather slowly under t h e influence of the dilute acids used. At t h e time these tests were made Yellow AB and Yellow OB apparently were not being used in food products a n d were said t o b e 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.
