Dr. Schunck on the Formation of Indigo-blue. 89 



caustic soda. After being filtered from this precipitate, the 

 liquid appeared of a beautiful purple colour. It was mixed with 

 an excess of acetic acid and distilled or evaporated to about one 

 quarter of its original volume, and then mixed with a large 

 quantity of water, which precipitated the whole of the matter 

 dissolved in it in the shape of dirty purple flocks. These flocks 

 were collected on a filter, well washed with water, and then treated 

 with dilute causlic soda, which generally, however, only dissolved 

 a minute portion of them. After being again filtered off and 

 well washed, they were dried and treated with a small quantity 

 of cold alcohol. The alcohol dissolved a portion, forming a 

 solution of a deep reddish-yellow colour, which was filtered and 

 evaporated, when it left a shining resinous substance of the same 

 colour, which, as it possesses characteristic properties and a 

 peculiar composition, I shall call Indifulvine. By dissolving it 

 in weak spirits of wine it was separated from a little impurity, 

 which remained undissolved in the shape of a brown powder. 

 The matter left undissolved by the cold alcohol consisted chiefly 

 of indirubine. For the purpose of purifying this body, I availed 

 myself of the property which it possesses, in common with 

 indigo-blue, of dissolving in caustic alkalies in the presence of 

 bodies which easily take up oxygen. On treating the mixture 

 containing indirubine with a solution of protoxide of tin in caustic 

 soda and boiling, I obtained a solution which, after being rapidly 

 filtered, deposited indirubine on exposui'e to the air in the shape 

 of a reddish-purple pellicle covering ifs surface. This pellicle, 

 on being broken, fell to the bottom in thick flakes and was suc- 

 ceeded by another. As soon as the whole of the indirubine 

 contained in it had been again oxidized and deposited, it was 

 filtered off, well washed with water and dissolved in boiling 

 alcohol. The alcoholic solution, which had a beautiful purple 

 colour, generally left on evaporation a dark brown amorphous 

 residue, consisting of indirubine in as high a state of purity as I 

 have been able to obtain it when formed by the decomposition 

 of indican. A brown powder was left undissolved by the alka- 

 line solution of protoxide of tin, which, after being again treated 

 with a fresh quantity of the same solution in order to dissolve 

 all the indirubine which might bo contained in it, was washed 

 with water, then with acid, washed again with water, dried and 

 treated M'ith cold alcoliol. The latter dissolved a second portion 

 of indifulvinc!, wliich seemed to liave escaped the solvent action 

 of the alcohol in the first instance, in consequence of its having 

 been so intimately mixed with and enveloped by partich's of in- 

 dirubine as not to be i-eached by tlie alcohol. The alcohol still 

 left undissolved a quantity of brown ])owder, which did jiot seem 

 to be any j)cculiar substance, but an intimate mixture of iudiful- 



