Dr. Schunck on the Formation of Indigo-blue, 119 



The second analysis afforded the following data : — 



II. 0-3125 grm. gave 0-8975 grm. carbonic acid and 0-1635 

 water. 



0-3400 grm. gave 0-4635 grm. chloride of platinum and am- 

 monium. 



Hence may be deduced the following composition : — 



Eqs. Calculated. Found. 



If the first formula be doubled, it gives C** H^" N'^ 0«; and if 

 from this be deducted one equivalent of water and two equiva- 

 lents of oxygen, it gives the second formula, C'^'* H'^ N^ 0^. 



For the sake of distinction I think it may be of advantage to 

 apply to the first of these modifications of indifulvine the term 

 a-indifulvine, and to the second that of ^-indifulvine. The man- 

 ner in which these bodies are derived from iudican can only be 

 understood after all the products of decomposition have been 

 treated of. 



Indihumine. 



This substance has the appearance of a sepia-brown powder, 

 which is insoluble in water and alcohol, but soluble in alkaline 

 liquids, forming brown solutions, from which it is reprecipitatcd 

 by acids in brown flocks. When heated on platinum it burns 

 without melting, leaving some charcoal which easily burns away. 

 Boiling nitric acid decomposes it easily, forming a yellow solution, 

 which on evaporation leaves an orange-coloured residue insoluble 

 in water. Indihumine is not always formed in any great quan- 

 tity in the decomposition of indicau by acids. Sometimes, indeed, 

 it cannot be detected among the products of decomposition, and 

 usually it is present only in minute quantities. What are the 

 circumstances which determine its formation in particular cases 

 I am unable to say. On the only occasion on which I obtained 

 a sufficient quantity for analysis, it w^as procured from an alcoholic 

 extract of woad by evaporating, adding water to the residue and 

 filtering, then adding sulphuric acid to the watery solution con- 

 taining iudican, filtering again, allowing the solution to stand 

 for twenty-four hours, filtering off" the indigo-blue and other 

 products which had separated, boiling the liquid, collecting the 

 brown ])owder which was deposited during the ebullition on a 

 filter, washing it with water, and then treating it with a boiling 

 mixture of alcohol and ammonia until nothing more dissolved. 



