FORMATION OF INDIGO-BLUE. 203 



The behaviour of indirubine towards concentrated sulphuric 

 acid and towards alkaline solutions of deoxidising substances 

 so much resembles that of indigo-blue towards the same re- 

 agents as to lead one to expect a great similarity in the com- 

 position of the two bodies, even if the fact of their being 

 formed from the same parent substance by the same process 

 of decomposition were unknown. The quantity of pure indi- 

 rubine, which I obtained from the leaves of the Indigofera, was 

 only sufficient for a general examination of its properties and 

 for one analysis, which showed however, if it be permitted to 

 draw a positive conclusion from one determination, that it has 

 exactly the same elementary composition as indigo-blue, that 

 the two substances are isomeric, rhe following are the num- 

 bers yielded by the analysis : — 



0.3185 grm. dried at 100°C and burnt with oxide of copper 

 and chlorate of potash gave 0.8500 grm. carbonic acid and 

 0.1195 water. 



0.2021 grm. gave 49.3 CC. of nitrogen at a temperature of 

 10.5°'C. and a pressure of 269.5 mm equivalent to 16.81 CC. 

 at 0° C. and a pressure of 760 mm or 0.2122 grm.* 



In 100 parts in contained therefore 



Carbon 72.78 



Hydrogen . 4.16 



Nitrogen ... 10.50 



Oxygen 12.56 



.00 



Indifulvinb. 



This substance is obtained on the evaporation of its alco- 

 holic solution in the form of a deep reddish-yellow, transparent, 

 amorphous resin, which when dry is brittle and may easily be 

 reduced to powder. It is perfectly insoluble in caustic alkalies, 



small red crystals, which seem to consist of pure indirubine. They are insoluble 

 in caustic alkalies, but soluble in boiling alcohol, the solution depositing on 

 cooling, crystals exactly like those abore described. 



' I owe this determination to Professor Frankland, who had the kindness to 

 perform it according to bis own method of analysis. 



