IP 



J)r. Hofmann on Aniline-blue. 



[Nov. 19, 



phenomena whicli characterize the transition of rosaniline into its blue 

 derivative ; again, the several processes of purification to which the crude 

 product is submitted have thrown much Hght upon the chemical character 

 of the compound. 



MM. Girard and De Laire, whose names are so intimately associated 

 with tlie development of the new colour-industry, have pointed out that the 

 passage from red to blue is attended by an evolution of torrents of am- 

 monia ; and Mr. Nicholson, who combines the genius of the manufacturer 

 with the habits of the scientific inquirer, has ascertained that the blue 

 colouring matter is invariably a saline compound of a base itself colourless, 

 like rosaniline. But the relations between the two colourless bases, and 

 consequently the nature of the reaction by which rosaniline is converted 

 into the blue colouring matter, had hitherto remained unknown. 



It was therefore with great pleasure that I accepted the kind offer of my 

 friend Mr. Nicholson to supply me with the necessary materials for the 

 elucidation of this question. 



The salt transmitted to me, and which Mr. Nicholson had prepared 

 himself, was the chloride. 



Hydrochlorate. — ^This compound is an indistinctly crystalline powder 

 of a bluish-brown colour, which at 100° becomes pure brown. It is 

 perfectly insoluble in water, cold or boiling — so much so, indeed, that it 

 imparts no colour to the water with which it is washed. It is Ukewise 

 insoluble in ether, but dissolves, although with difficulty, in alcohol, 

 which assumes the magnificent deep-blue tint characteristic of this colour- 

 ing matter. The boiling saturated alcoholic solution deposits the chloride 

 on cooling in the form of imperfect crystalline granules. The alcoholic 

 solution, when evaporated, leaves the compound as a thin film, which 

 reflects the light with a peculiar metallic, half-golden, half-coppery lustre. 



The hydrochlorate has the same composition whether dried in vacuo 

 or at 100°. Several analyses made with specimens of different preparations 

 lead unmistakably to the expression 



_C33H,,N3C1. 



This formula contains the history of aniline-blue, pointing out as it does 

 not only its chemical character and the relation in which it stands to 

 rosaniline, but explaining also, in the most satisfactory manner, the reac- 

 tion by which the passage from red to blue is accomplished. 



The simple and natural interpretation of the formula which I have 

 given, exhibits the new compound in the light of the hydrochlorate of 

 triphenylic rosanihne 



C33 H3, N3 C1=C,, H,e (C3 H,)3 N3, HCl, 

 when the process of transformation becomes represented by the equation 

 H,, N3, HCl + 3 C^H^' = (C^ H,)3 N3, Ha 3H3N. 



Rosaniline-salt. Aniline. Salt of triphenylic rosaniline. Ammonia. 



* The relation between aniline-red and aniline-blue is already pointed out in a short 

 note submitted to the Royal Society a few weeiis ago. — A. \V. H. 



