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amounts of bromine in large amounts of air required well designed absorption vessels. That involved a lot of fundamental work by physical chemists on the study of the absorption of bromine and chlo rine by sodium carbonate under differ ent circumstances. That in its turn meant a lot of important analytical work in connection with the deter mination of the proportions of bromine and chlorine wrhich had interacted with certain sodium carbonate solutions and, further, the amounts of bromine and chlorine present in the atmosphere above such sodium carbonate solutions. It was only with the aid of accurate work of this kind that really sound in formation could be obtained about the equilibria involved.
Organic Analyses
I have dealt with two industries, basically inorganic in character, and at this stage I should like to turn to the organic side. I was concerned, at one time, during the war, in the manufacture of two or ganic substances which may help to give pointers to the importance of anal ysis in industrial work. We were concerned on the one hand with the production of carbamite and on the other with that of monomethylaniline.
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was made, if I remember rightly, as a constituent of flashless cordite. Carbamite was produced by the interaction of a monoethylaniline-diethylaniline mixture of high diethylaniline content with phosgene in the presence of sodium carbonate. The point I want to emphasize, however, is that the secondary and tertiary amines had been produced by ethylation of aniline with ethyl chloride. The aniline was produced by the hydrogénation of nitrobenzene. That particular preparation involved the very efficient fractionation of aniline from traces of nitrobenzene (order of 0.02%). We had to determine those amounts. Inconsistent results indicated that our analytical method was not good enough. We were using the established method—i.e., reduction of the nitrobenzene in a stream of carbon dioxide with titanous salt, followed by back-titration of the excess titanous with ferric solution using thio-
cyanate as indicator. We had to employ a large amount of titanous in order to make sure that the nitrobenzene was reduced immediately and not lost in the stream of carbon dioxide. That, of course, involved arriving at the proportion of nitrobenzene by means of the difference between two very large titrations. Really that was a variation of the old flea and elephant idea, and unsatisfactory. Obviously we had to think in other terms, and that is how we came to think in terms of polarographic reduction—i.e., in terms of a simple and direct determination of that nitrobenzene. Briefly, the method we employed was as follows : To 2 ml. of the sample of nitrobenzene is added 0.5 ml. of a solution of 0.1 gram of nigrosine in 100 ml. of concentrated hydrochloric acid. The nigrosine is added as maximum suppressor. The mixture is shaken thoroughly until the aniline hydrochloride fumes eventually produced have dissolved completely. The liquid is then transferred to the cell of the polarograph (Cambridge) and polarographed over the range 0 to —1.4 applied voltage. In deducing a step height, 45° tangents are drawn to the curve at the beginning and end of the nitrobenzene step and the vertical distance between the points of contact of the curve is then measured. The test is standardized in terms of known nitrobenzene-aniline mixtures. As a result of all this, our accuracy was now of the order of two in the third place, instead of two in the second place, thus enabling more satisfactory calculations to be made of the performance of fractionating columns. I would like to mention another matter. During the war, when it became very important to increase aircraft speed, various substances like monomethylaniline were added to the liquid fuel with this object in view. This was made by the methylation of aniline which was produced by the hydrogénation process previously described. Now the effective control of the purity of the product obtained from that plant was an analytical control. It did, in effect, mean boxing of the aniline, monomethylaniline, dimethylaniline compass and, moreover, by relatively simple and direct methods. We had to get away from the diazotization procedure. In the case of the determination of the aniline, we took advantage of the fact that aniline reacts with picryl chloride in ethyl acetate solution to yield a picrylamine and, in turn, liberates hydrochloric acid. On treatment of the reaction mixture with sodium bicarbonate solution, an equivalent of sodium chloride is produced, which is titrated electrometrically with standard silver ANALYTICAL
CHEMISTRY
