Dissociation of Aniline Colours, 137 



I. Rosaniline. 



300 cubic centims. of a solution of rosaniline acetate or hy- 

 drochloride containing -0003 grm. in a litre of water are com- 

 pletely decolorized by half an hour's heating to ebullition ; 

 15 cubic centims. of this solution lose their colour in a few 

 minutes. Either of these bleached solutions will then readily 

 impart unaltered colouring-matter to a piece of immersed 

 silk. 



In order to avoid any possible bleaching effect due to any 

 alkali that might be extracted from glass vessels by a boiling 

 aqueous fluid, an experiment was made in a large platinum 

 dish, with precisely the same results as before. We are there- 

 fore clearly dealing with a real case of dissociation ,*the rosa- 

 niline and its hydric acetate (or chloride) remaining in pre- 

 sence of one another without combination. In this respect 

 these salts well maintain their known general analogy with 

 sal-ammoniac. 



In order to ascertain whether the dissociation would be re- 

 versed by prolonged preservation at the ordinary temperature, 

 some of the bleached liquid was cooled, set aside, and observed 

 from day to day. At the end of thirty days a considerable 

 proportion of the colour somewhat suddenly returned. 



The success of this experiment naturally induced me to try 

 the effect of cooling the liquid, as a means of accelerating the 

 return of the colour. Some of it was placed in a tube and 

 cooled down to —17° C, when it of course solidified; the 

 solid mass, when thawed, had a decided red colour. 



The colour of the boiling liquid is restored, as might have 

 been expected, by addition of a trace of acid. The tempera- 

 ture of boiling water appears to be that at which, in this case, 

 complete dissociation is best effected. 



II. Mauveine. 



A solution of mauveine acetate, of the same strength as in 

 (I.), is bleached, by boiling, in much the same time as that of 

 rosaniline. A solution of double that strength refuses to 

 bleach, even when boiled for several hours. Silk immersed in 

 the boiling decolorized liquid is immediately dyed. The colour 

 can be restored, and the dissociation therefore reversed, either 

 by freezing or by keeping at the ordinary temperature for several 

 days ; and the colour of the boiling liquid can be again brought 

 out by addition of a trace of hydric salt. 



III. JVicholson s Blue. 

 Unlike the preceding salts of amines, Nicholson's blue is a 





