OCt., 1917 THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY 953 with stirring, and the flask allowed to stand. The ascertaining the presence of aniline, the calcium hypo- solution, when the precipitate has settled, is filtered chlorite test is employed. The quantitative deter- through a Gooch crucible, using a bell jar arrangement, mination is carried out by precipitating the aniline into a 250 to 300 cc. Erlenmeyer flask. The crucible as tribromoaniline with bromine water. The precipi- is fitted preferably with a small circular filter paper tate is caught on a tared filter paper, dried in vacuo, (cut to size) instead of asbestos. The flask should be and weighed. washed with wash-ether (100parts absolute ether and In this connection, it occurred to the writer that it 2 parts alcoholic HC1) while filtering so as not to allow might be possible to work out, for estimating the any ferric chloride to dry on the white precipitate or aniline, a colorimetric method based on the qualita- on the crucible. The usual precautions of washing the tive test with hypochlorite. If this were possible, flask, crucible and funnel are taken to insure complete it certainly would be desirable, for not only would transfer of iron. It is not necessary, however, to trans- considerable time and effort be saved but probably fer all of the aluminum chloride precipitate to the a considerably smaller sample than IO liters would be Gooch crucible. The aluminum precipitate is removed sufficient and quantitative measurements could also with the paper from the crucible by tapping it into a be applied in cases where the amount of aniline in 25 cc. beaker and then washing with water to remove the samples available, or that can be conveniently adhering particles. The original flask is also washed collected, is too small for the gravimetric determina- to transfer completely any adhering aluminum pre- tion. A detailed study of the hypochlorite test for cipitate. The aluminum chloride solution is diluted aniline was therefore undertaken. to approximately IOO cc., about 5 g. ammonium ni- trate are dissolved in it, and made just alkaline‘ with THE HYPOCHLORITE TEST FOR ANILINE ammonia (using methyl red as indicator, preferably), The hypochlorite test for aniline is described by boiled, filtered and the precipitate is washed in the usual various authors in rather indefinite language. Thus way. The precipitate is ignited in a covered crucible2 Blythl in describing this test simply states that an and weighed as A1203. The ether solution of iron is aqueous solution of aniline or its salts is colored blue distilled or evaporated to remove the ether. The by “a little” chloride of lime or hypochlorite of soda. residue is transferred with a little water and HC1 Heffter,2 although stating that an excess of the reagent to a weighed platinum dish, using as little water as pos- should be avoided, does not give any information as sible, and evaporated to dryness on the steam bath, to the proper strength of the hypochlorite solution moistened with I cc. concentrated H2S04, warmed or what amount of it to use for a given volume of the on the steam bath gently to expel most of the HC1, solution to be tested. All the information given is and then slowly over a flame by placing the dish on contained in the statement that on adding to the a triangle which in turn is put on an asbestos gauze aqueous solution of aniline, chloride of lime or sodium (to prevent too rapid heating), and heated until all hypochlorite solution, a purplish violet coloration ap- the ferric chloride is converted to sulfate and no further pears which later changes to a dirty red. That the fuming of sulfuric acid takes place. The dish is then proportion of hypochlorite to aniline and the degree heated over a free flame and finally over a blast to of their concentration are, however, important factors entirely convert the sulfate to ferric oxide. This is and hence should be taken into consideration in ap- then cooled and weighed as okide in the usual plying this test, appears conclusively proven by the manner. following results: BUREAUOF CHEMISTRY DEPARTMENTOF AGRICULTURE EFFECT OF VARYING THE PROPORTION OF WASEINGTON.D. C. HYPOCHLORITE That the proportion of hypochlorite used for a given A METHOD FOR THE COLORIMETRIC ESTIMATION amount of aniline is an important factor in the test, OF SMALL AMOUNTS OF ANILINE even when the cdncentration of the aniline remains the same, and that in certain cases it may even cause By ELIASELVOVE a change in the result from ’negative to positive, is Received August 27, 1917 shown by the results obtained in the following experi- In the sanitary examination of air in industrial es- ment. To each of two small tubes there was added tablishments where aniline is employed, the detection 0.5 cc. of a 0.02 per cent aqueous solution of aniline. and estimation of aniline vapors is quite important. No. I was then mixed with 0.5 cc. of a calcium hypo- A method for this purpose has been worked out by chlorite solution, the available chlorine of which was Hebert and Heim.3 According to these authors, about I per cent; No. 2 was similarly treated with the aniline vapors are collected by bubbling IO liters 0. j cc. of a calcium hypochlorite solution, the avail- of the air through a suitable absorption bulb contain- able chlorine of which was only about 0.I per cent. ing IO cc. of water acidified with sulfuric acid. For Immediately after mixing, No. I developed the charac- 1 W Blum. “Determination of Aluminum as Oxide,” Scientific Papers teristic purplish color but No. 2 appeareds practically of the Bureau of Standards No. 286. colorless. 2 The difficulties involved in the accurate determination of alumina are not generally known and the reader is referred to the exhaustive work by 1 “Poisons: Their Effects and Detection,” 4th Ed., p. 285. Doctor Blum OD this subject. * Neuberg. “Der Ham.” 1 (1911), 831. 8 Rev. chim. ind., 11, 338-340; from Chem. Abs., 6 (1911), 791. 8 On standing a little while, however, a slight yellowish color developed. 9 54 THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY Vol. 9, No. IO

EFFECT OF VARYING THE CONCENTRATIOK N NaOH, a decided yellow color developed in a few That simply varying the concentration of the hypo- minutes while the solution which did not receive this chlorite and aniline, even without changing the pro- treatment remained practically colorless in compari- portion of either, also has a decided effect on the re- son. sults obtained, may be seen from the following ex- TIME OF ADDING ALKALI periment. To each of two tubes there was added It appears also that in order for the added alkali I cc. of a 0.I per cent aqueous solution of aniline. to act as sensitizer, it is necessary to add it after the No. I was diluted to z cc. with distilled water while aniline solution has been mixed with the hypochlorite No. z was diluted to 20 cc. with the same water. Each reagent, as may be seen from the following experi- was then mixed with 0.5 cc. of a calcium hypochlorite ment. To each of two tubes there was added 0.1 cc. solution, the available chlorine of which was about I of a 0.I per cent aqueous solution of aniline and each per cent. Immediately after mixing, a very decided was diluted to 20 cc. with distilled water. No. I was purplish color developed in No. I while in No. z no mixed first with I cc. of the calcium hypochlorite purplish color appeared but a yellowl color developed. solution1 and after standing about a minute was then The reason why the hypochlorite test for aniline mixed with I cc. of N NaOH while No. 2 was mixed has not heretofore been made the basis of a colori- first with I cc. of the N NaOH and after standing metric method for estimating small amounts of ani- about a minute was then mixed with I cc. of the same line is probably to be found in the fact that the pur- hypochlorite solution. After the final mixing with the plish color ordinarily obtained is very unstable and I cc. N NaOH, No. I began to develop color and had hence cannot well be made the basis of a quantitative a very decided yellow color after it had stood about method. Also the solution often acquires more or IO minutes, but No. z appeared practically colorless in less turbidity and thus still further complicates the comparison, in spite of the fact that, excepting for the problem. It was found, however, that none of these reverse order in which the reagents were added, it difficulties is encountered with the yellow color ob- had received exactly the same treatment as No. I. tained under the conditions of the above experiment (sol. No. z), since this color does not possess the very SENSITIVENESS OF THE TEST fugitive character of the purplish color but is sufficiently Since the hypochlorite test for aniline, in one or stable to admit of its being utilized for quantitative other of its modifications, is probably the most charac- purposes; nor is reading of the colors made difficult on teristic of the various color tests for aniline which have account of turbidity, since under the conditions which been proposed, it seemed desirable in this connection favor the formation of the yellow color, the solution to determine its sensitiveness by the improved pro- remains clear, at least sufficiently long so as not to cedure here described. According to Dragendorff ,* interfere with the readings. These results, therefore, I part aniline in 6,000 parts water is the minimum con- indicated the feasibility of making the hypochlorite centration which will yield a positive test with calcium test the basis of a colorimetric method for estimating hypochlorite. According to Jacquemin,2 the sensi- small amounts of aniline, provided the conditions were tiveness of the test can be increased so as to detect I chosen which would yield the yellow color instead of part aniline in 10,000 parts water by substituting the purplish. sodium hypochlorite in place of the calcium hypo- SENSITIZING EFFECT OF ADDED ALKALI chlorite employed by Dragendorff. It was found, however, that by basing the test on the yellow color was found that the addition of alkali to the mixed It instead of the purplish and taking advantage of the solutions of aniline and hypochlorite, which were above described sensitizing effect of added alkali, mixed under the conditions referred to above as yield- even as little as 0.01mg. in 20 cc., or I part in 2,000,- ing the yellow colors, has the effect of sensitizing the 000, could be readily detected. reaction, so that a distinct yellow color is obtained even with an amount of aniline which is too small PROCEDURE ADOPTED to show any color in the absence of this treatment, The following procedure was finally adopted. A as may be seen from the following experiment. To preliminary teSt was carried out on the. solution to each of two tubes there was added 0.I cc. of a 0.I be examined, with the object of obtaining an idea as per cent aqueous solution of aniline and sufficient to the approximate amount of aniline present. If distilled water to make 20 cc. Each was then mixed this indicated that its concentration was more than I with I cc. of calcium hypochlorite solution, the avail- part in zoo,ooo, the solution was dilutedS with distilled able chlorine of which was about 0.I per cent. On water so as to make it come within the range of the letting these solutions stand the usual period of IO standards (I pt. in about 28j,000 to I pt. in z,ooo,ooo) minutes, no appreciable color developed. On now I Containing 0.1 per cent available chlorine. mixing,. however, one of these solutions with I CC. of 2 See Jacquemin. Comfit. rend., 83 (1876), 226. 1 This fact, besides enabling one to utilize this test for quantitative 8 Instead of diluting the solution to be examined, one may also Prepare purposes, as is shown in this paper, can help also to make the hypochlorite a set of standards with correspondingly higher aniline concentrations. For test for aniline more characteristic, for, when the regular purplish color example, a series of standards may be prepared having ten times the con- is obtained, the result could be confirmed on another portion of the same centration of those used in this work and reading 0. 0.1, 0.2, 0.3. 0.4, 0.5. sample by varying the concentration, as shown above, so as to obtain the 0.6 and 0.7 mg., respectively. In using such a higher series of standards, yellow color; and then the result could be still further confirmed by showing however, it appears more advantageous to adopt a little longer interval that this yellow color is much increased by adding alkali, as is shown in than 10 minutes for the tubes to stand before being read, when one has another pert of this paper. occasion to use the higher end of the series. OCt., 1917 THE JOCR,VAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY 955

used; 20 cc. of this solution was then mixed with I probably close enough for most practical purposes, cc. of calcium hypochlorite solution,* the available and also to the thousandth of a milligram (the figures chlorine of which was 0. I per cent. After standing in the parentheses) where the amount given or found 2 minutes, it was mixed with I cc. of N SaOH and was not in even hundredths. The average error (neg- allowed to stand IO minute^.^ The color of this solu- lecting the algebraic signs) was practically the same tion was then compared with those of standards, (0.003 mg.) whether we accept the figures expressing which were obtained by treating similarly known the amounts of aniline to the nearest hundredth of a amounts of a standard aniline solution. The mixing milligram or to the thousandth of a milligram. These with the reagents and the final reading of the color results further confirm the general principle that from was carried out in the same tube, the narrow form the point of view of percentage accuracy it is well jo cc. Nessler tubes having been found convenient to work with as large amounts as possible within the for this purpose. The mixing of the unknown solu- given range, since an error of only 0.003 mg. in the tion and the standards with the reagents was effected case of No. 6 shows up as a much greater percentage nearly simultaneously with the aid of bulbed glass error than even over three times this amount (0.OIO rods, by means of which it was found comparatively mg.) in the case of No. 3. very easy to mix thoroughly the contents of four or Finally, when we recall that by the ordinary applica- five tubes practically simultaneously. The stand- tion of the hypochlorite test for aniline even the solu- ards were prepared from a stock solution of pure ani- tion with the highest of the above amounts of aniline line in distilled water, which contained I gram aniline (No. 3) would not show even qualitatively the pres- in 1,000cc. of solution. The regular4 standards con- ence of any aniline while the proposed method measures tained 0, 0.01,0.02, 0.03, 0.04,0.05, 0.06 and 0.07 such small amounts quantitatively, and the further mg. aniline, respectively, and the volume of each, ex- fact that this method does not require elaborate ap- clusive of the reagents, was 20 cc. paratus but is very simple and quickly and easily car- RESULTS OBTAINED ried out, its advantages when one has occasion to de- The following results were obtained by the above tect and estimate such small amounts of aniline, be- procedure when working with aqueous solutions of come very apparent. HYGIENICLABORATORY aniline, the amount of aniline in which was unknown5 U. S. PUBLICHEALTH SERVICE to the writer at the time the work was done. WASHINGTON,D. C. MILLIGRAMSANILINE IN 20 Cc KO. Given Found Error 1 ...... 0.04 0.04 0.00 (0.000) A MODIFICATION OF THE PRICE METHOD FOR THE 2...... 0.02 (O:Oi4) 0.02 (0:023) 0.00 (-0.001) 3 ...... 0.18 ... 0.17 -0.01 (-0.010) SEPARATION OF THE PERMITTED COAL-TAR 4...... 0.11 ... 0.11 (o:ios) 0.00 (-0.00s) 3 ...... 0.03 (0.032) 0.03 (0.032) 0.00 (0.000) COLORS TO INCLUDE TARTRAZINE 6 ...... 0.01 (0.014) 0.02 (0.017) 4-0.01 (C0.003) AVERAGE...... 0.003 0.003 By E. H. INCERSOLL As will be noted, the amounts of aniline are expressed , Received July 2, 1917 to the nearest one-hundredth of a milligram, which is Food Inspection Decision 76, issued by the U. S. 1 Since it is important that the unknown solution and the standards Department of Agriculture in 1907, enumerated seven be mixed with the reagents as nearly simultaneously as possible, it is well coal-tar colors that could be used in foods under cer- 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. tain restrictions. Price’ in 1911 described a method 2 This solution was prepared by suitably diluting with water a stock for the separation of these colors when they occurred solution, the available chlorine of which was about 3 per cent, which was in mixtures. Recently, under Food Inspection Deci- obtained by shaking thoroughly for 10 minutes 20 g. of a sample of com- mercial chlorinated lime with 100 cc. water and then filtering. This stock sion 164, there has been another coal-tar dye added to solution shouid not be prepared from a chlorinated lime which has lost much the seven previously permitted, namely, Tartrazine. of the available chlorine that it originally had, since it might leave too much The including of this additional color among the per- calcium in the final reagent and thus cause a precipitate or turbidity when the excess alkali is added. mitted ones makes it necessary for the analyst to have 8 In the case of the standard containing the smallest amount of aniline available a method whereby these eight coal-tar dyes (0.01 mg.), reducing this time of standing to 5 minutes appears advantageous. 4 For most practical purposes these standards are probably sufficient, may be separated and identified in cases where they since in case the color of the unknown solution happens to fall between two occur in mixtures. Estes2 has stated the necessity of the above standards one can, especially after some experience, judge for such a method and gives a modification of the which of the two standards it approaches nearer and assign it a proper intermediate value which will probabiy be close enough for most practical method described by Price to include this additional purposes. When dealing with the middle and especially the lower end of color. By this method Amaranth is separated from the above series of standards, however, since there would be greater possi- Tartrazine by saturating the aqueous solution of these bility for a larger percentage error, it is advisable to confirm any such as- sumed value by actually preparing the corresponding standard and one a two dyes with sodium chloride; however, it has been little above and another a little below that value and repeating the simul- observed that when but small amounts of dye have taneous treatment with the reagents. In order to enable one to prepare quickly and easily such intermediate standards, it is advisable to have on been taken out of the original mixture on extraction hand a more dilute solution of aniline than the above mentioned stock solu- with the ammonium sulfate reagent, the separation tion Such a solution was prepared by diluting 10 cc. of the stock solution is very difficult if at all attainable. Furthermore, to 1000 cc. with distilled water,which has also the advantage that the volume used in the preparation of any standard, expressed in cc., gives also the while some Tartrazine, like Naphthol Yellow S, is solu- value of that standard in hundredths of a milligram of aniline. By keeping ble in saturated ammonium sulfate solution, the larger some of this dilute solution in an appropriate burette, any desired inter- mediate standard was quickly and easily prepared. part is not extracted by this reagent, if the Price direc- These solutions were submitted to the writer as “unknowns” by Dr. 1 U. S. Department of Agriculture, B. A. I. Circular 180. A. Seidell. of this laboratory. 2 THISJOURNAL, 8 (1916), 1123-1124.