I N D U S T R I A L A N D ENGINEERING CHEMISTRY
A m i 1 15. 1931
225
A New Test for the Halogens' H. Earl Tremain OAK DALE DRIVE,SALINA, KAN.
HILE working with p-aminodimethylaniline, it was W found that it gave a very sensitive color reaction with a n uncombined halogen. This compound may be obtained by the decomposition of methyl orange by hydrogen sulfide. An easier method is to purify the technical product obtainable in the market. This is done by simply distilling the crude material to remove the colored impurities that would mask the reaction. p-Aminodimethylaniline is a light brown crystalline substance, melting a t 41' C. and boiling a t 262' C. It is soluble in water, alcohol, ether, and chloroform, and darkens and decomposes upon exposure to light, air, and moisture. To prepare the reagent, dissolve Sgramsof p-aminodimethylaniline in 100 cc. of absolute alcohol. The alcohol permits less decomposition than water if used as the solvent. To make the test, 2 or 3 drops af the reagent are added to 5 cc. of water and the solution to be tested slowly added. only enough should be introduced to produce a clear pink color, or other confusing colors may result. For example, if a 1
Received November 7, 1930.
0.01 per cent solution of bromine be added a drop a t a time to 5 cc. of the reagent, the following colors will appear in turn: pink, red, purple, violet-red, green, brown, and yellow, all definite colors formed by the successive halogenation of the benzene nucleus and the methyl side chains in quite a complex manner. The reagent when properly used will detect 1 part Br in 1,300,000 of water 1 part C1 in 65,000 of water 1 part I in 400,000 of water
A convenient though less sensitive method of making the test is with test papers made by dissolving 10 cc. of p-aminodimethylaniline in 100 cc. of absolute alcohol. A good grade of filter paper is immersed in this solution and dried. It is then cut into small strips, a strip dropped into 5 cc. of water, and the solution to be tested slowly added. Both the strips and the reagent must be kept in dark, tightly stoppered bottles. The test should be made in a neutral or slightly acid solution, as an excess of acid will destroy the color, whereas a large amount of alkali would combine with the halogen.
NOTES AND CORRESPONDENCE Determination of Oxides of Nitrogen (except Nitrous Oxide) in Low Concentration
We have investigated the Francis and Parsons method thoroughly, but have found that it is not. possible to obtain satisfactory results by it unless a blank is subtracted to account for the impurity of the hydrogen peroxide. On the other hand, after modifying the method as described, we were able to obtain results of higher accuracy, without the use of a blank.
tioned that the directions given by Piccard, Peterson, and Bitting for the preparation of our absorbing and oxidizing solution are not those given by us. The quantity of this solution used for each analysis as stated by them, while having an equivalent oxidizing power, contains nearly six times the quantity of sulfuric acid used by us. (3) We think that a fair view of Piccard, Peterson, and Bitting's paper is that it confirms the accuracy of our method within the limits claimed-namely, that of color comparison in Nessler tubes, which is usually taken to be 5 per cent. I n addition, the paper shows that our method may be modified so as to be s&able for use with gas mixtures containing halogen compounds which might be fixed in the solution used for absorbing the oxides of nitrogen. A. G. FRANCIS A. T. PARSONS
(1) It might be inferred from the paragraph quoted above that in our method no account was taken of the possible presence of determinable nitrogen in the reagents used and in the air of the room, and, further, that when this is done, the proportion of such nitrogen found is relatively large. Such inference is entirely wrong. The performance of a blank is an integral part of our method; the magnitude of this blank, as stated in our paper (page 267), never exceeded 0.0015 mg. of nitrogen. (2) I n the modification now proposed by Piccard, Peterson, and Bitting, standards are prepared each time by the same process as that used in the actual analysis. If this is done with all the reagents used in the analysis, full compensation is obtained for the quantity of determinable nitrogen in the reagents and in the air of the room. But the magnitude of this compensation is not determined. It appears to us that the prudent chemist will desire t o have this information. Incidentally it may be men-
Editor of Industrial and Engineering Chemistry: To the three points raised by Francis and Parsons, we should like to reply as follows, making it clear from the beginning that we have in no way the intention of belittling the work of these authors. (1) The paper of Francis and Parsons was, a t the time we started our work, the only paper on which we could rely in order t o get results a t all. We found, however, that for our purpose certain modifications were necessary, We were not able t o secure any hydrogen peroxide of sufficient purity to allow us to use such a great excess as Francis and Parsons did. They use 0.07 of 50 ml. of a 7l/2 per cent hydrogen peroxide solution which makes about 0.3 gram of hydrogen peroxide. We found
Editor of Industrial and Engineering Chemistry: In a paper under this title, Piccard, Peterson, and Bitting Anal. Ed., 2,294 (1930)] record the results of [IND.ENG.CHEM., their investigation of the method of determination of oxides of nitrogen published by us in the Analyst, 50, 262 (1925). In summarizing their conclusions they say :
GOVERNMENTLABORATORY LONDON, W. C. 2, ENGLAND November 25, 1930
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