'IMATION OF INDIGO-BU 191 



A watery solution of indican on being mixed with 



oxalic or tartaric acid and left to stand yields a dark blue or 



purple deposit, consisting of indigo-blue and indirubine, which 



ii oxalic acid is employed, are remarkably free from other 



acts of decomposition. The liquid filtered from tin-, 

 depo- in either case when boiled a few more flocks, 



ifter being filtered, mixed with sulphuric acid and boiled 



i, it gives an additional quantity. These flocks contain 

 indirabine and iudirctiue but no indigo-blue. Even acetic 

 acid produces a slight effect on indican. On adding that acid 

 to a watery solution of the latter, the mixture deposits on 

 standing some dark flocks, consisting of indigo-blue and in- 

 dirubine, but their quantity is trifling. 



A more minute examination of this process of decomposition 



el that it was more complicated and that the products 

 formed by it were more numerous than I had at first imagined. 



products of decomposition which I have observed are of 

 three kinds. The first are insoluble in water and are deposited 

 in the shape of powder or flocks from the acid liquid, the 

 second remain dissolved in the latter, the third are volatile and 

 are obtained by distilling the liquid either whilst the action 

 of the acid is proceeding or after it has ceased. For the pur- 

 pose of preparing these various products I found it to be 



pessary to obtain indican in a state of absolute purity by 

 successive solution in alcohol, water and ether, for though 

 some indican is always decomposed when its watery solution 

 is evaporated, the substances into which it is* thereby 

 converted afford by decomposition with acids, products 

 which do not differ in their nature, but only in their 

 relative proportions from those which are formed, when 

 perfectly pure indican is employed. I therefore contented 

 myself with extracting the dry leaves of the woad plant with 

 cold alcohol, evaporating the extract in the apparatus above 

 described, adding water to the residue and filtering. The 



ion of indican thus obtained was mixed with a considerable 



