Dr. Schunck on the Formation of Indigo -blue. 121 



phurous acid. A boiling solution of bichromate of potash, to 

 which sulphuric acid is added, dissolves and decomposes it 

 rapidly with an evolution of gas, the chromic acid being reduced 

 to oxide of chromium. On being treated with boiling dilute 

 nitric acid, indifuscine is decomposed with a disengagement of 

 nitrous acid, giving a yellow liquid, which on evaporation yields 

 crystals of oxalic acid. The mother-liquor of these crystals, on 

 being neutralized with carbonate of potash and evaporated, gives 

 brownish-yellow crystals, which detonate when heated, and give 

 with acetate of lead, nitrate of silver, and sulphate of iron, reac- 

 tions showing them to consist of picrate of potash. When finely- 

 powdered indifuscine is suspended in water and subjected to the 

 action of chlorine, it is converted into a yellow flocculent sub- 

 stance containing chlorine, which is insoluble in boiling water, 

 but dissolves easily in boiling alcohol, forming a brown solution, 

 which on spontaneous evaporation leaves a light brown amor- 

 phous residue. 



When the indican submitted to decomposition with acids has 

 not been purified, the quantity of indifuscine formed far exceeds 

 that of the other products of decomposition, which, with the 

 exception of indigo-bhie, are always produced in comparatively 

 small quantities. In this case a great part of the indifuscine 

 owes its origin to the action of the acid on a body formed by the 

 influence of water and oxygen on indican. Nevertheless, even 

 when perfectly pure indican is employed, a certain quantity of 

 indifuscine is always produced, especially if the quantity of ma- 

 terial used is considerable. 



When submitted to analysis, indifuscine prepared on difi'erent 

 occasions is found to exhibit considerable variation in its com- 

 position. The analyses, the results of which I am about to give, 

 were made with specimens derived from difi^erent sources, which, 

 notwithstanding the diflFerence in their composition, showed no 

 difference in their properties. 



I. 0'3135 grm. indifuscine, obtained from the deposit formed 

 on mixing a watery solution of indican with sulphuric acid and 

 allowing the mixture to stand in the cold, dried at 100° C. and 

 burnt with oxide of copper and chlorate of potash, gave 0'6830 

 grm. carbonic acid and 0-1305 water. 



II. 0"3930 grm., obtained by adding sulphuric acid to a 

 watery solution of indican, allowing the mixture to stand for 

 some time in the cold, filtering, and then employing the deposit 

 produced on heating the filtered liquid, gave 0*8720 grm. car- 

 bonic acid and 0*1G25 water. 



0-5G75 grm. gave 0*5230 grm. chloride of platinum and am- 

 monium. 



III. 0-31'35 grm., derived from the deposit formed on mixing 



