OCt., 1917
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 M I S T R Y
with stirring, and t h e flask allowed t o stand. T h e solution, when t h e precipitate has settled, is filtered through a Gooch crucible, using a bell jar arrangement, into a 2 5 0 t o 300 cc. Erlenmeyer flask. T h e crucible is fitted preferably with a small circular filter paper (cut t o size) instead of asbestos. T h e flask should be washed with wash-ether (100parts absolute ether a n d 2 parts alcoholic HC1) w h i l e f i l t e r i n g so as not t o allow a n y ferric chloride t o dry on t h e white precipitate or on t h e crucible. T h e usual precautions of washing t h e flask, crucible a n d funnel are taken t o insure complete transfer of iron. It is not necessary, however, t o transfer all of t h e aluminum chloride precipitate t o t h e Gooch crucible. T h e aluminum precipitate is removed with t h e paper from t h e crucible b y tapping i t into a 2 5 cc. beaker a n d then washing with water t o remove adhering particles. The original flask is also washed t o transfer completely a n y adhering aluminum precipitate. The aluminum chloride solution is diluted t o approximately I O O cc., about 5 g. ammonium nit r a t e are dissolved in i t , a n d made just alkaline‘ with ammonia (using methyl red as indicator, preferably), boiled, filtered a n d t h e precipitate is washed in t h e usual way. The precipitate is ignited in a covered crucible2 and weighed as A1203. T h e ether solution of iron is distilled or evaporated t o remove t h e ether. T h e residue is transferred with a little water a n d HC1 t o a weighed platinum dish, using as little water as possible, a n d evaporated t o dryness on t h e s t e a m b a t h , moistened with I cc. concentrated H2S04, warmed on t h e steam b a t h gently t o expel most of t h e HC1, a n d t h e n slowly over a flame by placing t h e dish on a triangle which in t u r n is p u t on a n asbestos gauze (to prevent too rapid heating), a n d heated until all t h e ferric chloride is converted t o sulfate a n d no further fuming of sulfuric acid takes place. The dish is then heated over a free flame a n d finally over a blast t o entirely convert t h e sulfate t o ferric oxide. This is t h e n cooled a n d weighed as okide in t h e usual manner.
ascertaining t h e presence of aniline, t h e calcium hypochlorite test is employed. T h e quantitative determination is carried out b y precipitating t h e aniline as tribromoaniline with bromine water. The precipit a t e is caught on a tared filter paper, dried in v a c u o , a n d weighed. I n this connection, i t occurred t o t h e writer t h a t i t might be possible t o work out, for estimating t h e aniline, a colorimetric method based on t h e qualitative test with hypochlorite. If this were possible, i t certainly would be desirable, for not only would considerable time and effort be saved b u t probably a considerably smaller sample t h a n I O liters would be sufficient a n d quantitative measurements could also be applied in cases where t h e amount of aniline in t h e samples available, or t h a t can be conveniently collected, is too small for t h e gravimetric determination. A detailed study of t h e hypochlorite test for aniline was therefore undertaken. THE HYPOCHLORITE TEST FOR ANILINE
The hypochlorite test for aniline is described by various authors in rather indefinite language. Thus Blythl in describing this test simply states t h a t a n aqueous solution of aniline or its salts is colored blue by “ a little” chloride of lime or hypochlorite of soda. Heffter,2 although stating t h a t a n excess of t h e reagent should be avoided, does not give any information as t o t h e proper strength of t h e hypochlorite solution or what amount of i t t o use for a given volume of t h e solution t o be tested. All t h e information given is contained in t h e statement t h a t on adding t o t h e aqueous solution of aniline, chloride of lime or sodium hypochlorite solution, a purplish violet coloration appears which later changes t o a dirty red. T h a t t h e proportion of hypochlorite t o aniline a n d t h e degree of their concentration are, however, important factors and hence should be taken into consideration in applying this test, appears conclusively proven b y t h e following results:
BUREAUOF CHEMISTRY DEPARTMENT OF AGRICULTURE WASEINGTON. D. C.
A METHOD FOR THE COLORIMETRIC ESTIMATION OF SMALL AMOUNTS OF ANILINE By
ELIASELVOVE
Received August 27, 1917
I n t h e sanitary examination of air in industrial establishments where aniline is employed, t h e detection a n d estimation of aniline vapors is quite important. A method for this purpose has been worked out b y Hebert a n d Heim.3 According t o these authors, t h e aniline vapors are collected by bubbling I O liters of t h e air through a suitable absorption bulb containing I O cc. of water acidified with sulfuric acid. For 1 W Blum. “Determination of Aluminum as Oxide,” Scientific Papers of the Bureau of Standards No. 286. 2 The difficulties involved in the accurate determination of alumina are not generally known and the reader is referred to the exhaustive work by Doctor Blum OD this subject. 8 Rev. chim. ind., 11, 338-340; from Chem. Abs., 6 (1911), 791.
953
EFFECT OF VARYING THE PROPORTION OF HYPOCHLORITE
T h a t t h e proportion of hypochlorite used for a given amount of aniline is a n important factor in t h e test, even when t h e cdncentration of t h e aniline remains t h e same, and t h a t in certain cases i t may even cause a change in t h e result from ’negative t o positive, is shown by the results obtained in t h e following experiment. T o each of two small tubes there was added 0 . 5 cc. of a 0 . 0 2 per cent aqueous solution of aniline. No. I was then mixed with 0 . 5 cc. of a calcium hypochlorite solution, t h e available chlorine of which was about I per cent; No. 2 was similarly treated with 0.j cc. of a calcium hypochlorite solution, t h e available chlorine of which was only about 0 .I per cent. Immediately after mixing, No. I developed t h e characteristic purplish color b u t No. 2 appeareds practically colorless. 1
“Poisons: Their Effects and Detection,” 4th Ed., p. 285.
8
On standing a little while, however, a slight yellowish color developed.
* Neuberg. “Der Ham.” 1 (1911), 831.
9 54
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 EFFECT O F V A R Y I N G T H E C O N C E N T R A T I O K
T h a t simply varying the concentration of the hypochlorite and aniline, even without changing t h e proportion of either, also has a decided effect on the results obtained, may be seen from the following experiment. T o each of two tubes there was added I cc. of a 0.I per cent aqueous solution of aniline. No. I was diluted t o z cc. with distilled water while No. z was diluted t o 2 0 cc. with the same water. Each was then mixed with 0 . 5 cc. of a calcium hypochlorite solution, t h e available chlorine of which was about I per cent. Immediately after mixing, a very decided purplish color developed in No. I while in No. z no purplish color appeared but a yellowl color developed. T h e reason why t h e hypochlorite test for aniline has not heretofore been made the basis of a colorimetric method for estimating small amounts of aniline is probably t o be found in t h e fact t h a t the purplish color ordinarily obtained is very unstable and hence cannot well be made t h e basis of a quantitative method. Also t h e solution often acquires more or less turbidity and thus still further complicates the problem. It was found, however, t h a t none of these difficulties is encountered with the yellow color obtained under t h e conditions of t h e above experiment (sol. No. z ) , since this color does not possess t h e very fugitive character of t h e purplish color b u t is sufficiently stable t o admit of its being utilized for quantitative purposes; nor is reading of t h e colors made difficult on account of turbidity, since under t h e conditions which favor t h e formation of t h e yellow color, t h e solution remains clear, a t least sufficiently long so as not t o interfere with t h e readings. These results, therefore, indicated t h e feasibility of making t h e hypochlorite test t h e basis of a colorimetric method for estimating small amounts of aniline, provided the conditions were chosen which would yield the yellow color instead of t h e purplish. S E N S I T I Z I N G EFFECT O F A D D E D A L K A L I
It was found t h a t t h e addition of alkali t o t h e mixed solutions of aniline and hypochlorite, which were mixed under t h e conditions referred t o above as yielding t h e yellow colors, has t h e effect of sensitizing t h e reaction, so t h a t a distinct yellow color is obtained even with a n amount of aniline which is too small t o show any color in t h e absence of this treatment, as may be seen from t h e following experiment. T o each of two tubes there was added 0 .I cc. of a 0.I per cent aqueous solution of aniline and sufficient distilled water t o make 2 0 cc. Each was then mixed with I cc. of calcium hypochlorite solution, t h e available chlorine of which was about 0 .I per cent. On letting these solutions stand the usual period of I O minutes, no appreciable color developed. On now mixing,. however, one of these solutions with I CC. of 1 This fact, besides enabling one to utilize this test for quantitative purposes, as is shown in this paper, can help also to make the hypochlorite test for aniline more characteristic, for, when the regular purplish color is obtained, the result could be confirmed on another portion of the same sample by varying the concentration, as shown above, so as to obtain the yellow color; and then the result could be still further confirmed by showing that this yellow color is much increased by adding alkali, as is shown in another pert of this paper.
Vol. 9, No.
IO
N NaOH, a decided yellow color developed in a few minutes while t h e solution which did not receive t h i s treatment remained practically colorless in comparison. TIME OF ADDING ALKALI
It appears also t h a t in order for t h e added alkali t o act as sensitizer, it is necessary t o add it after t h e aniline solution has been mixed with the hypochlorite reagent, as may be seen from t h e following experiment. To each of two tubes there was added 0.1 cc. of a 0 .I per cent aqueous solution of aniline and each was diluted t o 2 0 cc. with distilled water. No. I was mixed first with I cc. of t h e calcium hypochlorite solution1 and after standing about a minute was then mixed with I cc. of N NaOH while No. 2 was mixed first with I cc. of t h e N NaOH and after standing about a minute was then mixed with I cc. of t h e same hypochlorite solution. After t h e final mixing with t h e I cc. N NaOH, No. I began t o develop color a n d h a d a very decided yellow color after it had stood about I O minutes, but No. z appeared practically colorless in comparison, in spite of t h e fact t h a t , excepting for t h e reverse order in which t h e reagents were added, i t had received exactly t h e same treatment as No. I . SENSITIVENESS O F THE TEST
Since t h e hypochlorite test for aniline, in one o r other of its modifications, is probably t h e most characteristic of t h e various color tests for aniline which have been proposed, it seemed desirable in this connection t o determine its sensitiveness by t h e improved procedure here described. According t o Dragendorff ,* I p a r t aniline in 6,000 parts water is t h e minimum concentration which will yield a positive test with calcium hypochlorite. According t o Jacquemin,2 t h e sensitiveness of t h e test can be increased so as t o detect I part aniline in 10,000 parts water by substituting sodium hypochlorite in place of t h e calcium hypochlorite employed by Dragendorff. I t was found, however, t h a t by basing the test on t h e yellow color instead of the purplish and taking advantage of t h e above described sensitizing effect of added alkali, even as little as 0.01mg. in 2 0 cc., or I part in 2 , 0 0 0 , 000, could be readily detected. PROCEDURE ADOPTED
The following procedure was finally adopted. A preliminary teSt was carried out on the. solution to be examined, with the object of obtaining an idea as t o t h e approximate amount of aniline present. If this indicated t h a t its concentration was more t h a n I part in zoo,ooo, t h e solution was dilutedS with distilled water so as t o make it come within t h e range of t h e standards ( I p t . in about 2 8 j,000 t o I p t . in z,ooo,ooo) Containing 0.1 per cent available chlorine. See Jacquemin. Comfit. rend., 83 (1876), 226. 8 Instead of diluting the solution to be examined, one may also Prepare a set of standards with correspondingly higher aniline concentrations. For example, a series of standards may be prepared having ten times the concentration of those used in this work and reading 0. 0.1, 0.2, 0.3. 0.4, 0.5. 0.6 and 0.7 mg., respectively. In using such a higher series of standards, however, it appears more advantageous to adopt a little longer interval than 10 minutes for the tubes to stand before being read, when one has occasion to use the higher end of the series. I
2
OCt., 1917
T H E JOCR,VAL O F 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
955
probably close enough for most practical purposes, and also t o t h e thousandth of a milligram (the figures in t h e parentheses) where t h e amount given or found was not in even hundredths. The average error (neglecting t h e algebraic signs) was practically t h e same (0.003 mg.) whether we accept the figures expressing t h e amounts of aniline t o t h e nearest hundredth of a milligram or t o t h e thousandth of a milligram. These results further confirm t h e general principle t h a t from the point of view of percentage accuracy i t is well t o work with as large amounts as possible within t h e given range, since a n error of only 0 . 0 0 3 mg. in t h e case of No. 6 shows up as a much greater percentage error t h a n even over three times this amount ( 0 . O I O mg.) in t h e case of No. 3. Finally, when we recall t h a t by t h e ordinary application of t h e hypochlorite test for aniline even t h e solution with t h e highest of t h e above amounts of aniline (No. 3) would not show even qualitatively t h e presence of any aniline while t h e proposed method measures such small amounts quantitatively, and the further fact t h a t this method does not require elaborate apparatus but is very simple and quickly and easily carried out, its advantages when one has occasion t o detect and estimate such small amounts of aniline, become very apparent.
used; 2 0 cc. of this solution was then mixed with I cc. of calcium hypochlorite solution,* t h e available chlorine of which was 0 . I per cent. After standing 2 minutes, i t was mixed with I cc. of N S a O H and allowed t o s t a n d I O minute^.^ The color of this solution was then compared with those of standards, which were obtained by treating similarly known amounts of a standard aniline solution. The mixing with t h e reagents a n d t h e final reading of t h e color was carried out in t h e same tube, t h e narrow form j o cc. Nessler tubes having been found convenient for this purpose. The mixing of t h e unknown solution and t h e standards with t h e reagents was effected nearly simultaneously with t h e aid of bulbed glass rods, b y means of which i t was found comparatively very easy t o mix thoroughly t h e contents of four or five tubes practically simultaneously. The standards were prepared from a stock solution of pure aniline in distilled water, which contained I gram aniline in 1,000cc. of solution. The regular4 standards contained 0, 0.01,0 . 0 2 , 0 . 0 3 , 0.04,0.05, 0 . 0 6 and 0.07 mg. aniline, respectively, a n d t h e volume of each, exclusive of t h e reagents, was 2 0 cc. RESULTS OBTAINED
The following results were obtained by t h e above procedure when working with aqueous solutions of aniline, t h e amount of aniline in which was unknown5 t o t h e writer a t t h e time t h e work was done.
HYGIENICLABORATORY U. S. PUBLICHEALTHSERVICE WASHINGTON, D. C.
MILLIGRAMS ANILINEIN 20 Cc Given Found Error 1 .......... 0.04 0.04 0.00 (0.000) 2. 0.02 (O:Oi4) 0.02 ( 0 : 0 2 3 ) 0.00 (-0.001) 3 0.18 ... 0.17 -0.01 (-0.010) .......... 0 . 1 1 ... 0.11 (o:ios) 0.00 (-0.00s) 3 .......... 0.03 (0.032) 0 . 0 3 (0.032) 0.00 (0.000) 6 0.01 (0.014) 0.02 (0.017) 4-0.01 (C0.003) AVERAGE. .................................... 0.003 0.003
KO.
A MODIFICATION OF THE PRICE METHOD FOR THE SEPARATION OF THE PERMITTED COAL-TAR
......... ..........
4 ..........
As will be noted, t h e amounts of aniline are expressed t o t h e nearest one-hundredth of a milligram, which is Since i t is important that the unknown solution and the standards be mixed with the reagents as nearly simultaneously as possible, it is well to use pipettes or burettes with comparatively large outflow openings, so as to consume as little time as possible for the adding of the reagents. 2 This solution was prepared by suitably diluting with water a stock solution, the available chlorine of which was about 3 per cent, which was obtained by shaking thoroughly for 10 minutes 20 g. of a sample of commercial chlorinated lime with 100 cc. water and then filtering. This stock solution shouid not be prepared from a chlorinated lime which has lost much of the available chlorine that it originally had, since it might leave too much calcium in the final reagent and thus cause a precipitate or turbidity when the excess alkali is added. 8 In the case of the standard containing the smallest amount of aniline (0.01 mg.), reducing this time of standing to 5 minutes appears advantageous. 4 For most practical purposes these standards are probably sufficient, since in case the color of the unknown solution happens to fall between two of the above standards one can, especially after some experience, judge which of the two standards it approaches nearer and assign i t a proper intermediate value which will probabiy be close enough for most practical purposes. When dealing with the middle and especially the lower end of the above series of standards, however, since there would be greater possibility for a larger percentage error, i t is advisable to confirm any such assumed value by actually preparing t h e corresponding standard and one a little above and another a little below t h a t value and repeating the simultaneous treatment with the reagents. In order to enable one t o prepare quickly and easily such intermediate standards, i t is advisable to have on hand a more dilute solution of aniline than the above mentioned stock solution Such a solution was prepared by diluting 10 cc. of the stock solution to 1000 cc. with distilled water,which has also the advantage t h a t the volume used in the preparation of any standard, expressed in cc., gives also t h e value of t h a t standard in hundredths of a milligram of aniline. By keeping some of this dilute solution in an appropriate burette, any desired intermediate standard was quickly and easily prepared. These solutions were submitted t o the writer as “unknowns” by Dr. A. Seidell. of this laboratory. 1
COLORS TO INCLUDE TARTRAZINE By E. H. INCERSOLL
,
Received July 2, 1917
Food Inspection Decision 76, issued by t h e U. S. Department of Agriculture in 1907, enumerated seven coal-tar colors t h a t could be used in foods under certain restrictions. Price’ in 1911 described a method for t h e separation of these colors when they occurred in mixtures. Recently, under Food Inspection Decision 164, there has been another coal-tar dye added t o t h e seven previously permitted, namely, Tartrazine. The including of this additional color among t h e permitted ones makes i t necessary for t h e analyst t o have available a method whereby these eight coal-tar dyes may be separated and identified in cases where they occur in mixtures. Estes2 has stated t h e necessity for such a method and gives a modification of t h e method described by Price t o include this additional color. By this method Amaranth is separated from Tartrazine by saturating the aqueous solution of these two dyes with sodium chloride; however, i t has been observed t h a t when b u t small amounts of dye have been taken out of t h e original mixture on extraction with t h e ammonium sulfate reagent, t h e separation is very difficult if a t all attainable. Furthermore, while some Tartrazine, like Naphthol Yellow S, is soluble in saturated ammonium sulfate solution, t h e larger part is not extracted b y this reagent, if t h e Price direc1
U. S. Department of Agriculture, B. A. I. Circular 180.
2
THISJOURNAL, 8 (1916), 1123-1124.
