44 Dr. Schunck on the Furmation of Indigo-blue. 



further heated becomes recl^ aud on boiling, yellow. The whole of 

 the substance is dissolved without leaving any resinous residue, 

 such as is always left when indigo-blue is treated with nitric acid, 

 forming a clear yellow solution. This solution leaves on evapo- 

 ration a residue which dissolves only partially in hot water. A 

 brown resinous substance is left undissolved by the latter, and 

 the liquid filtered from this is bright yellow and very bitter, and 

 yields, when mixed with carbonate of potash and evaporated, 

 crystals, apparently of picrate of potash, which detonate when 

 heated. Very dilute nitric acid also decomposes and dissolves it 

 on boiling, but its decomposition is effected with far more diffi- 

 culty than that of indigo-blue by the same means. In like man- 

 ner a boiling solution of bichromate of potash, mixed with sul- 

 phuric acid, which easily decomposes indigo-blue, seems to have 

 verj' little effect on it even when the boiling is continued for a 

 considerable time. ^Vhen suspended in water and exposed to 

 the action of a sti-eam of chlorine gas, it loses its colour very 

 slowly, and is changed into a brown resinous substance con- 

 taining chlorine, which melts in boiling water and is easily solu- 

 ble in alcohol, but does not crystallize when the solution is eva- 

 porated. Like the indirubine from iudican, it is quite insoluble 

 in alkaline liquids, but dissolves easily when a deoxidizing agent, 

 such as grape-sugar or a protosalt of iron or tin, is added at the 

 same time. If it be treated for instance with a solution of prot- 

 oxide of tin in an excess of caustic soda it dissolves rapidly, 

 forming a yellow solution, the surface of which on exposure to 

 the air instantly becomes covered with a film of regenerated in- 

 dirubine, the appearance being exactly like that of an indigo vat, 

 except that the film floating on the surface is purple instead of 

 blue. If a piece of calico be dipped into the solution and then 

 exposed to the air it acquires a purple colour, which is not re- 

 moved either by acids or soap. This colour has no great inten- 

 sity, but by working on a larger scale, it is probable that shades 

 of purple equal in depth to those produced by indigo-blue might 

 be obtained. When the solution is mixed with an excess of 

 muriatic acid, it gives a dirty yellow precipitate, which after 

 filtration and exposure to the air slowly becomes purple. By 

 long-continued exposure of the solution to the atmosphere the 

 whole of the indirubine dissolved in it is again deposited as a 

 purple mass, which is sometimes found to consist of small cry- 

 stalline needles. When heated in a tube with soda-lime, the 

 substance emits fumes having a smell like that of benzole and an 

 alkaline reaction, which condense on the colder parts of the tube 

 to a sublimate, consisting partly of oil and jiartly of crystalline 

 needles. It is not precipitated from its alcoholic solution by 

 acetate of lead, even when ammonia is added at the same time. 



