THE JOURNAL of INDUSTRIAL and ENGINEERING CHEMISTRY 953 with Stirring, and the Flask Allowed to Stand
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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.