198 MR. E. SCHUNCK ON TBM 



Indirubine. 

 This substance when obtained by the process above de- 

 scribed usually appears in the form of a dark brown amor- 

 phous mass. On one occasion, when very pure indican had 

 been employed in its preparation, it was deposited from the 

 boiling alcoholic solution on cooling in long crystalline needles, 

 which were red by transmitted light. The alcoholic solution 

 has a fine purple colour. It is perfectly insoluble in alkaline 

 liquids, but if it be treated with a boiling solution of caustic 

 soda, to which some deoxidising substance, such as pro to- 

 chloride of tin or grape sugar is added, it dissolves with ease, 

 just as indigo-blue does under the same circumstances, form- 

 ing a solution from which it is again deposited in purple 

 flakes by the action of the atmospheric oxygen. It dissolves 

 in concentrated sulphuric acid in the cold, forming a purple 

 solution, which on the addition of water gives a dark precipi- 

 tate, the supernatant liquid remaining of a fine purple colour. 

 It is decomposed by boiling nitric acid. On being heated 



sulphur, he obtained in three analyses 72.90, 72.84, and 72.97 per cent, of 

 carbon, which correspond apparently with the theoretical composition. These 

 amounts are, however, calculated according to the old atomic weight of carbon. 

 If corrected in accordance with the new atomic weight of carbon, which was 

 established by Dumas a short time previously, they become respectively 71-89, 

 75.77, and 71.92, the great excess in the second determination being probably 

 due to some misprint. On analysing some specimens of the indigo-blue re- 

 maining from his previous investigation, which he himself had proved to be 

 impure, and calculating the results according to the new atomic weight of 

 carbon, Dumas obtained in four analyses 73.3, 73.5, 72.7, and 73.3 per cent, 

 of carbon. The coincidence between these and the previous annlyses is of 

 course only apparent. I have myself always found a deficiency in the amount 

 of carbon, unless care was taken to wash the precipitated indigo-blue for a 

 considerable time. I ascribe this circumstance to the indigo -blue like all 

 porous bodies combining with certain substances and removing them from 

 their solutions in consequence of an attraction of surface exerted by it. If, 

 for instance, grape sugar is employed in its purification, a certain quantity of 

 it is carried down by the indigo-blue and can only be removed by continuous 

 washing with hot water, followed by treatment with muriatic acid and renewed 

 washing with water. Each portion of water is found to leave on evaporation 

 a small quantity of syrup, and this does not cease until the washing has been 

 ontinued for several days. 



