Preparation of aniline black.

The Galaxy 7, 1876

The salts of vanadium have been found to play a very important part in the preparation of aniline black, and consequently in organic chemistry. If one centigramme of vanadous chloride or vanadate of ammonia is introduced into a normal mixture for aniline black, composed of 100 grammes water, 8 grammes hydrochlorate of aniline, and 3½ to 4 grammes chlorate of potash, the liquor quickly darkens and deposits aniline black abundantly. In forty-eight hours the reaction is nearly complete, and the fluid appears to have solidified, for the water is taken up by the black, which forms a thick paste. The black is intense and beautiful, and an important future for it in dyeing and printing is anticipated. But this reaction is still more striking in a chemical point of view. As studied out by M. A. Guyard, it appears to be one of the most elegant reactions of chemistry. One part of either vanadous chloride or vanadate of ammonia will transform 1,000 parts of hydrochlorate of aniline into the aniline black. "We make aniline black," says this chemist, "just as we set fire to fuel by means of a match. The power of the vanadium salts in the production of aniline black is more than a thousand times greater than that of copper. The reason of this is intelligible if we know the properties of vanadium. There is no metal which passes more readily from the lowest to the highest stage of oxidation, and returns again to the lowest. Under the feeblest reducing influences vanadie oxide becomes vanadous oxide, and under the faintest oxidizing influences vanadous oxide is reconverted into the vanadic. This is the whole secret of the power of vanadium, a power so great that the author thought at first he had encountered a new force, or at least one of those mysterious agencies called catalytic; but a closer study of the phenomenon soon led to its explanation." "If we introduce vanadic oxide or an alkaline vanadate into hydrochlorate of aniline, the vanadic salt is instantly reduced to the state of vanadous oxide or chloride. If we introduce into a mixture of an aniline salt and of a chlorate 11000 of vanadous chloride, or of a vanadate, aniline black is produced with the same energy." In this case the chlorate is decomposed with disengagement of chlorine, and the vanadous salt is peroxidized, and effects the transformation of the aniline salt. M. Guyard finds that none but those metals which have at least two degrees of oxidation in the moist way are capable of producing aniline black. Next to vanadium in point of delicacy of reaction stands copper, and yet it has but one thousandth part the force of vanadium. With both these metals the quantity employed is so small that it may be disregarded in considering the composition of the black. The vanadium aniline black is the same as the copper aniline black, and neither contains vanadium or copper. The delicacy of this reaction makes chloride of vanadium the best reagent for aniline, and conversely a mixture of hydrochlorate of aniline and chlorate of potash is the best reagent for vanadium. These researches add force to the investigations of Dr. Hayes in the universal diffusion of vanadium in rocks.

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