FOBMATION OF INDIGO-BLUE. 195 



purple flocks. These flocks were collected on a filter, well 

 washed with water and then treated with dilute caustic 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 Indt/ulvine. 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 in- 

 dirubine on exposure to the air in the shape of a reddish- 

 purple pellicle covering its surface. This pellicle on being 

 broken fell to the bottom in thick flakes and was succeeded 

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

 in it had been again oxidised and deposited, it was filtered off, 

 wol! washed with water and dissolved in boiling alcohol. The 

 alcoholic solution which had a beautiful purple colour generally 



OB 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 alkaline solu- 

 tion of protoxide of tin, which after being again treated 

 a fresh quantity of the same solution, in order to 



he all the indirubine which might be contained in it, 

 was washed with water, then with acid, washed again with 



