ANILINE-RED 185 



another base, the presence of which determines the formation of the colouring-matter. 

 The idea very naturally suggested itself that toluidine which, owing to the difficulty 

 of separating toluol from benzol, is always present in commercial anilines-might be 

 the true source of the colouring-matter. Experiments made with pure toluidine 

 showed, however, that this base is not more capable of yielding the red than pure 

 aniline itself. But the red colouring-matter is instantaneously produced when a mixture 

 of pure aniline and pure toluidine is treated with the chlorides of mercury or tin, or with 

 arsenic acid, plainly showing that the two bases must co-operate in the formation of 

 the red.' 



This result, Dr. Hofmann believes, contains the clue by which may be explained 

 not only the genesis of aniline-red, but also that of the tinctorial ammonias generally. 

 It points, moreover, to the necessity of ascertaining how far the formation of tho 

 violet and other colouring-matters, hitherto believed to be exclusively derived from 

 aniline, require the co-operation of toluidine. 



Keturning to tho red derivatives of aniline obtained by the different processes 

 above described, we may state broadly that all these products are composed essentially 

 of rosaniline salts. The red, prepared by the process of Messrs. Eonard and Franc, 

 or fuchsine, consists chiefly of hydrochlorate of rosaniline. The azaleine, or aniline- 

 red prepared by nitric acid, is principally nitrate of rosaniline. 



In the crude red, produced by the action of arsenic acid, we should find the arseniato 

 of rosaniline, which, by tho subsequent treatment, for tho sake of purification, is con- 

 verted into hydrochlorate or acetate of rosaniline; 



This is the place to record the fact that for some time past a coloiirless (or at least 

 slightly rose-coloured) paste, with an alkaline reaction, has been delivered into com- 

 merce from Mulhouse, in France ; which paste has only to be treated with acetic acid, 

 in which it dissolves Avith the greatest facility, in order to obtain an extremely rich 

 and beautiful carmine solution, capable of being at once employed for printing stuffs. 

 Now that the characters of rosaniline are known, there cannot be the least doubt that 

 this colourless paste, and certain pink powders of similar properties, consist almost 

 entirely of rosaniline more or less pure, and that they have been prepared by preci- 

 pitating a solution of a rosaniline salt by an excess of a powerful base, such as soda 

 or lime. 



Remarks on the Phenomena observed in the Applications of Aniline-Red. "We are now, 

 moreover, enabled to explain perfectly what takes place when a stuff which has been 

 dyed with aniline-red is acted upon by a powerful acid or alkali. On printing with a 

 powerful acid, the stuff is decolorised with the formation of a yellowish stain, because 

 a rosaniline salt with three equivalents of acid is formed ; the triacid salts of this 

 substance being in fact all yellowish, and possessing but little colour. When the 

 material is washed with water, the excess of acid is removed, and the monacid salt 

 reproduced, the red colour being restored. 



On printing with a powerful base, for example, with caustic soda, the red disappears 

 as tho red rosaniline salt is decomposed, and rosaniline liberated in a colourless con- 

 dition. But on washing out the soda with water, the red colour reappears, the 

 rosanilino becoming probably carbonated. 



If a powerful volatile base bo employed, as ammonia, the red also disappears, on 

 account of the liberation of the colourless rosaniline ; but in proportion as the 

 ammonia evaporates the red colouration returns, particularly on slightly warming as 

 the rosaniline, which is a fixed base, expels the ammonia, and re-forms the primitive 

 salt of rosanilino with its peculiar colour. If tho rosaniline-dyod fabric be left for a 

 considerable length of time (from twelve to twenty hours) in contact with weak 

 ammonia, the colour, as has been pointed out by Mr. W. Crum, scarcely returns on 

 rinsing with water. This is obviously due to the increased solubility of rosaniline in 

 water containing ammonia, which separates the colouring-matter even from tho 

 mordant. 



Tho salts of rosaniline, which are chiefly employed for dyeing silk and wool, 

 are tho acetate and the hydrochlorate, and their application is simple in the 

 extreme. The silk is dyed by passing it through a warm aqueous solution of the salt : 

 for the dyeing of wool the solution is heated to a temperature varying between 50 

 and 60 C. 



Tho force and rapidity with which rosaniline is fixed by silk and wool is the only 

 difficulty to be encountered in this branch of dyeing. In fact, this magnificent colour 

 is precipitated and fixed with such avidity and promptitude by silk and wool, that it 

 is necessary to take particular precautions, and to operate with solutions that are 

 at first comparatively weak, and are only gradually strengthened, to prevent the 

 dyeing being unequal, and the portions first immersed in the bath being more 

 strongly coloured than those afterwards introduced. Cotton is also difficult to dye 

 with rosaniline salts, but for the exactly opposite reason that it does not present any 



