490 



Dr. Hofmann on the Colouring Matters [Recess, 



in crude aniline* may become so minute that its presence can no longer 

 be traced by distillation, or by conversion into oxalates. It may be 

 recognized, however, with the utmost facility by submitting the mixture to 

 the action of either corrosive sublimate or arsenic acid ; on application of 

 a gentle heat the crimson colour is immediately produced. 



In the equations proposed by M. Schiff there figures, moreover, ammonia 

 as an essential term. The existence of ammoniacal salts in the crude 

 rosaniline was pointed out some time ago by Prof. Bolley. But this am- 

 monia (which, as I have satisfied myself, is scarcely ever absent) is, accord- 

 ing to my opinion, not an essential product of the reaction that gives rise 

 to the formation of aniline-red. I have established by special and careful 

 experiments that appropriate treatment of a mixture of aniline and tolui- 

 dine with chloride of mercury at a moderate temperature is capable of 

 producing very considerable quantities of rosaniline without elimination of 

 more than a trace of ammonia. The ammonia generally observed belongs 

 to a different phase of the reaction, being more especially due to the 

 almost invariable production of a small quantity of aniline-blue. 



If we wished, even now, to represent in formulae the relation between 

 rosaniline and the substances which give rise to its formation, the equation 



Ce H, N -h 2C, N = a„ N3 -f- 6H 



might be looked upon as an expression closely approaching truth. The 

 hydrogen figuring in this equation is eliminated in the form of water, 

 hydrochloric, hydrobromic, hydriodic acids, &c. 



But even this equation gives no account of the mechanism of this re- 

 markable process ; indeed we cannot hope for the solution of this chemical 

 problem before we shall have succeeded in splitting up the molecule of 

 rosaniline into the atomic groups which enter into its composition. It is 

 true its transformation into aniline- or toluidine-blue, as well as into the 

 several violets which are generated by the substitution of alcohol radicals, 

 prove even now that the rosaniline-molecule still contains three atoms of 

 typical hydrogen, and hence that the complex atom C^o H^g functions in 

 this triamine with the value of six atoms of hydrogen ; but this indeed 

 is the limit of the experimental evidence as yet obtained. 



With regard to the number and nature of the simpler radicals into which 

 the carbon and hydrogen atoms of the complex atom H^g are grouped, 

 we can only speculate. Derived from the radicals phenyl, Cg H5, and tolyl, 



H^, under the influence of dehydrogenating agents, this complex atom 



* Aniline obtained by distillation with potash from certain varieties of indigo, 

 is apt when treated with corrosive sublimate, to furnish traces of rosaniline. I 

 infer from this result that aniline thus produced contains a small proportion of 

 toluidine. The formation of this substance from indigo would be as readily 

 intelligible as the conversion under certain conditions of indigo into salicyhc acid, 

 a fact established by Cahours's observations. 



Aniline prepared from crystallized isatin does not yield a trace of rosaniline. 



