FORMATION OP INDIGO-BLUE. 209 



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 material used is considerable. 



When submitted to analysis indifuscine prepared on different 

 occasions is found to exhibit considerable variation in its 

 composition. The analyses, the results of which I am about 

 to give, were made with specimens, derived from different 

 sources, which notwithstanding the difference in their com- 

 ; on 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 de- 

 posit produced on heating the filtered liquid, gave 0.8720 grm. 

 carbonic acid and &1625 water. 



0.5675 grm. gave 0.5230 grm. chloride of platinum and 

 ammonium. 



III. 0.3435 grm. derived from the deposit formed on mix- 

 ing a decoction of woad leaves with muriatic acid and boiling, 

 gave 0.7635 grm. carbonic acid and 0.1510 water. 



0.4550 grm. gave 0.4365 grm. chloride of platinum and 

 ammonium. 



I V. 0.3675 grm. obtained by extracting fiuely chopped woad 

 leaves with warm water, adding sugar of lead to the extract, 



ing from the green precipitate, removing the excess of 

 lead with sulphuric acid, filtering, adding more acid, and treat- 

 ing the flocculent deposit which was formed in the usual 

 manner, gave 0.8950 grm. carbonic acid and 0.1635 war 

 0.5715 grm. gave 0.5855 grm. chloride of platinum and 



