180 ANILINE-BLUE 



Dr. Hofmann remarks that sulphuretted hydrogen is not fcy any moans the most 

 convenient reducing agent to effect this conversion, and he has shown that when 

 m'trobonzol is placed in contact with metallic zinc and hydrochloric acid, it is 

 rapidly converted into aniline. Bechamp submitted nitrobenzol to the action of 

 metallic iron and acetic acid, and thus transformed it into aniline. This process is 

 now almost universally adopted. Equal weights of nitrobonzol, acetic acid, and 

 cast-iron turnings are very gradually mixed in cast-iron vessels, so that the heat pro- 

 duced by the reaction does not raise the temperature of the mixture too high. The 

 semi-solid mass which is produced consists of .acetate of iron and acetate of aniline. 

 This is distilled sometimes alone, or by some manufacturers with the addition of lime ; 

 the distillate consisting generally of acetone, aniline, unaltered nitrobenzol, and 

 several other products arising from the impurity of the nitrobenzol. The crude 

 aniline mixture is redistilled, and the aniline obtained sufficiently pure by collecting 

 the products distilling between 175 C. and 190 C. Thus produced, aniline is a 

 slightly brownish liquid, a little heavier than water. 



ANlLiKTE-BIiACK. This colour can scarcely be said to have been satisfac- 

 torily produced. The green tints (see ANILINE-GREEN) are turned black, according 

 .to a process devised by Messrs. Wood and Wright, by mixing chlorate of potash 

 with a metallic salt and a salt of aniline ; for the metallic salt they prefer ferric 

 salts. Aniline-black may also be produced by treating the colour on the fabric by solu- 

 tions of bichromate of potash, or of weak bleaching-powder. Nitrate of copper 

 may be mixed with hydrochlorate of aniline, without the addition of chlorate of 

 potash, and the mixture printed on the fabric, when gradually a black tint is 

 produced. 



According to Brandt aniline-blacks are very variable in their composition and 

 properties. Some of them resist the action of light and of reagents much better than 

 others. Some turn of an unpleasant greenish hue if exposed to air charged with acid 

 or sulphurous vapours. The more intense an aniline-black the better it resists 

 reagents. It is true that this intensity depends partly on the degree of concentration 

 of the colour, but other circumstances influence its solidity. A black developed in 

 presence of an excess of aniline is always faster than one of the same degree of 

 concentration which is developed in presence of an excess of acid. In the latter case, 

 beside weakening the tissue, blacks are obtained which turn green, and cannot stand 

 the application of bleaching-powder. In this case, if the gas used for lighting the 

 premises contains a little sulphur, the fumes cause the folds of every piece in the 

 warehouse to turn green. 



With excess of base a black is produced which shows less disposition to turn green, 

 and bears chlorine better. Such a black must be developed rapidly enough to avoid 

 the volatilisation of the aniline. For this end chlorate of aniline is used instead of 

 chlorate of potash, diminishing the amount of the aniline salt by a corresponding 

 amount. Chlorate of potash, in presence of an excess of aniline, does not decompose 

 very rapidly. 



Aniline-blacks result from two distinct reactions. There is, firstly, decomposition 

 of the chlorate of aniline ; and secondly, oxidation of the other salt of aniline mixed 

 with the chlorate. The decomposition of the former gives rise to chlorinised products 

 derived from aniline. There are probably various stages of substitution a fact which 

 explains the diversity of the results. Besides these, there is formed another product, 

 the result of the oxidation of the salt of aniline. 



Aniline-black consists, therefore, of two distinct blacks : the one, formed of the 

 chlorine substitution of aniline, is exceedingly fast, and resists almost all chemicals, 

 but it is not so fine as that produced by a judicious mixture of the two blacks, as it 

 does not acquire its lustre and effect without the aid of the second. This latter is an 

 intense violet-blue, which appears black when concentrated. It is less solid than the 

 former, and turns greenish with the smallest amount of acid. It resists the action of 

 soap very well. The brown-black and blue-black mixed together form a fine aniline- 

 black. The object of the maker is to combine the maximum of beauty with the 

 maximum of solidity. This depends on the due proportion of the chlorate. 



Comparative trials have been made with pure aniline on the one hand, and, on the 

 other, with anilines containing toluidine and pseudo-tolmdine. The results were 

 similar in each case. 



AUlLlNE-BIiUE. MM. Girard and De Laire, in M. Pelouze's laboratory, dis- 

 covered the reactions which give rise to the aniline-blues. This reaction consists in 

 heating a salt of rosaniline, or a mixture of substances capable of giving rise to its 

 formation, for several hours with an excess of aniline. The blue colouring-matters 

 thus obtained are the Bleu de Paris and the Bleu do Lyons. The operation on a largo 

 scale is carried out by allowing the mixture of a salt of rosaniline, with an excess 

 of aniline, to digest at a temperature of 150 or 160 for a considerable time. If a 



