578 [May 21, 



and exposed to the action of the atmosphere, hydrazobenzol is gra- 

 dually reconverted into azobenzol. 



It deserves to be noticed that some of the chemists who have been 

 engaged in the examination of benzidine must have occasionally 

 worked with hydrazobenzol. Mr. Noble*, who many years ago 

 prepared benzidine in my laboratory, especially remarks that the 

 substance obtained by him is reconverted into azobenzol by the action 

 of nitrous acid. I have satisfied myself that benzidine thus treated 

 yields no trace of azobenzol. 



From the experiments described, it is obvious that in the forma- 

 tion of benzidine from azobenzol two distinct phases have to be dis- 

 tinguished : in the first phase the molecule of azobenzol assimilates 

 a molecule of hydrogen, but this hydrogen remains in a very feeble 

 state of combination, being eliminated again by a great variety of 

 agents. It is only under the influence of acids that the hydrogen 

 molecule becomes incorporated in the system, if I may use this ex- 

 pression, and fixed benzidine, a substance of great stability, is formed. 



Whatever view may be taken regarding the nature of azobenzol, 

 the constitution of which it must be admitted is utterly unknown, 

 the intermediate substance has to be viewed as its hydrogen com- 

 pound, and it is this consideration which induced me to propose the 

 name hydrazobenzol. 



VI. " Note on the Composition of Aniline-Blue." By A. W. 

 HOFMANN, LL.D., F.R.S., &c. Reeeived May 21, 1863. 



The prosecution of my researches on the aniline colours has led me 

 to a result of great simplicity, which I hasten to lay before the Royal 

 Society. 



Aniline-blue is triphenylic rosaniline. 



Aniline-red, Rosaniline C 20 H 19 N 3 , H 2 O. 



C 1 TT N H O 



Aniline-blue, Triphenylic Rosaniline .... * " . 3> 



V.v "5)3- 



The commercial article is a salt of the base, the hydrochlorate for 

 example, the composition of which corresponds to the monatomic 

 hydrochlorate of rosaniline. 



* Chem. Soc. Quart. Journ. vol. viii. p. 292. 



