486 Dr. Hofmann on the Colouring Matters [Recess, 



aniline) whicli I have lately communicated to the Royal Society (Proceed- 

 ings, June 16, 1864), naturally suggested the investigation of analogously 

 constituted bodies in a similar direction. My attention has in the first 

 place been directed to the study of a compound which, from its mode of 

 formation, ought to be designated as toluidine-blue. 



When a salt of rosaniline (the acetate for instance) is heated with double 

 its weight of toluidine, phenomena present themselves which are similar to 

 those observed in the analogous experiment with aniline. In the course of 

 a few hours the rosaniline passes through all the different shades of violet, 

 and is ultimately converted into a dark lustrous mass, which dissolves in 

 alcohol with a deep indigo-blue colour. This substance is the acetate of 

 tritolylrosaniline. By treatment with alcoholic ammonia, and subsequently 

 addition of water to the solution, the free base is easily obtained, from 

 which the several salts may be prepared by the usual processes. I have 

 examined only one of these salts, viz. the hydrochlorate. Repeatedly 

 crystallized from boiling alcohol, this salt is obtained in small blue crystals 

 insoluble in water, which at 100° C. contain 



C„ H3, N3 Cl=C,„(.(?g^)^ I N3, HCl. 



The formation of toluidine-blue is thus seen to be perfectly analogous to 

 that of aniline-blue. 



I have not examined in detail the properties of this new series of colour- 

 ing matters. Generally speaking they are more soluble than the corre- 

 sponding phenyl-compounds, and therefore less easily obtained in a state 

 of purity. 



"When one of these salts (the acetate for instance) is submitted to dry 

 distillation, water and acetic acid are evolved in the first place ; then follow 

 oily products, which, as the temperature rises, become more and more viscid 

 and ultimately solidify into crystalline masses, ammonia being abundantly 

 evolved during the latter stages of the process. Unless the operation has 

 been carried out on rather a large scale, a comparatively small amount of 

 a light porous charcoal remains in the retort. The oily distillate contains 

 several bases. Those boiling at a low temperature are almost exclusively 

 aniline and a little toluidine. The principal portion of the products boiling 

 at a higher temperature is a beautifully crystallized base which is easily 

 purified. By pouring cold spirit upon the interwoven crystals, a brown 

 mother liquor containing other bases is readily separated ; the residuary 

 substance has only to be crystallized from boiling alcohol in order to pro- 

 cure a compound of perfect purity. 



The chemical deportment of the new substance is very similar to that of 

 diphenylamine. Like the latter it unites with acids, forming salts of very 



