196 MR. E. SCHUNCK ON THE 



water, dried and treated with cold alcohol. The latter dis- 

 solved a second portion of indifulvine, which seemed to have 

 escaped the solvent action of the alcohol in the first instance 

 in consequence of its having been so intimately mixed with 

 and enveloped by particles of indirubine as not to be reached 

 by the alcohol. The alcohol still left undissolved a quantity of 

 brown powder, which did not seem to be any peculiar substance 

 but an intimate mixture of indifulvine and indirubine. The 

 indigo-blue left undissolved by the boiling alcohol was purified 

 by treating it according to Fritzsche's method with a warm 

 solution of grape sugar in alcohol to which caustic soda was 

 added, and allowing the mixture to stand in a warm place 

 until the indigo-blue was dissolved. The yellow solution 

 having been drawn off with a syphon and allowed to stand 

 exposed to the air became first red, then purple, and then 

 deposited the indigo-blue in the shape of small crystalline 

 scales, which were collected on a filter and washed first with 

 alcohol, afterwards with boiling water, then digested with 

 muriatic acid, well washed with water and dried. 



The bodies insoluble in water formed by the action of acids 

 on indican are therefore six in number. I shall now give an 

 account of their properties and composition. 



Indigo-blue. 

 The indigo-blue obtained by this process has all the pro- 

 perties usually ascribed to that substance. It is insoluble in 

 alkaline liquids, but dissolves easily when a deoxidising sub- 

 stance, such as a salt of protoxide of tin or protoxide of iron, 

 or grape sugar is added at the same time, the solution exhibit- 

 ing the usual appearance of an indigo vat, such as the yellow 

 colour, and the blue pellicle on the surface. It is only slightly 

 soluble in boiling alcohol, to which it communicates a blue 

 tinge, but easily and completely soluble in concentrated 

 sulphuric acid, forming a blue solution from which nothing 

 is precipitated on the addition of water. By the action of 



