1866.] 



Rosaniline to Rosolic Acid. 



211 



When an acid solution of a salt of rosaniline is mixed with nitrous acid, 

 it forms an azo-compound, which corresponds very closely in character to 

 diazobenzol. Like diazobenzol this compound forms explosive salts ; like 

 diazobenzol it decomposes with evolution of nitrogen gas when it is boiled 

 with acids. In adding the nitrous acid to the solution of rosaniline to 

 form the compound, it is easy to observe the exact point at which the so- 

 lution ceases to contain unaltered rosaniline. It thus becomes easy to 

 determine the amount of nitrous acid consumed in the conversion of a given 

 weight of rosaniline into the azo-compound. We have done this by the 

 employment of a method which gives excellent results when applied to 

 aniline and toluidine, and the details of which will shortly be published by 

 one of us. We obtain as the result of our experiments, that one molecule 

 of rosaniline consumes three equivalents of nitrous acid ; and the equation 

 representing the reaction will be 



Kosaniline. Azo-compound. 



C,JI,3N3 + 3HNO, = a,H,,N, + 611,0. 



On boiling this azo-compound with hydrochloric acid, there is evolution 

 of nitrogen gas. The volume of nitrogen was measured. The result was 

 that one molecule of rosaniline, after conversion into the azo-compound, 

 yields six equivalents of nitrogen. 



Azo-compound. 

 C,,H,,N, + 3H,0=C,,H,,03 + N,. 



These changes in composition are accompanied by striking physical 

 effects. The deep-red solution of the salt of rosaniline becomes brown 

 on the addition of excess of hydrochloric acid, then yellow as the nitrous 

 acid is added ; then there is much froth, and as the solution is boiled it 

 gradually becomes red yellow, and a large quantity of a deep-coloured solid 

 with cantharides-like lustre separates out. 



Seeing that this solid is produced by treating rosaniline with three equi- 

 valents of nitrous acid, and that six equivalents of nitrogen are evolved, it 

 must be a non-nitrogenous substance. A careful comparison of its pro- 

 perties and reactions with those of the rosolic acid described by Kolbe 

 and Schmitt, and now made largely as an article of commerce, leads to the 

 conclusion that it is identical with rosolic acid. 



The following characters are common to it and to the rosolic acid of 

 Kolbe and Schmitt. 



1. A yellowish-red solid with cantharides-like lustre, only sparingly 

 soluble in water, soluble in ether and alcohol. 



2. Easily soluble in ammonia, and in alkalies generally, forming red 

 solutions of very great colouring-power. Addition of acids to these solu- 

 tions decolorizes them, precipitating the colouring-matter in the form of a 

 yellowish precipitate, which varies much in tint. 



3. When boiled with aniline and a little benzoic acid, it forms a blue 

 dye, there being no evolution of ammonia. The blue dye is very soluble 



