FORMATION OF INDIGO-BLUE. 213 



The theoretical composition as compared with that derived 

 from these numbers is as follows : — 



I think it is improbable that the discrepancy between the 

 two formulae, which differ from one another merely by 3 HO, 

 proceeds from any impurity in either case, or that it is to be 

 attributed to the substance having been more carefully dried 

 at one time than at another. Indiretine appears to furnish 

 one of those instances, of which I have met with several 

 during the investigation of this series, of a body exhibiting 

 when prepared on different occasions the same properties but 

 having at one time a composition differing by the elements 

 of water from that which it has at others. 



Having described the several products of decomposition 

 formed by the action of acids on indican, which are insoluble 

 in water, I shall now proceed to the consideration of those 

 which are soluble in water. In order to obtain these I found 

 it advisable to employ sulphuric acid for the decomposition 

 of the indican. After the process was completed the insoluble 

 matter deposited wa3 separated by filtration, the sulphuric 

 acid was removed by means of carbonate of lead, and the 

 I having been filtered, sulphuretted hydrogen was passed 

 through it in order to precipitate a little lead contained in ir, 

 and after being again filtered it was evaporated by means of 

 a current of air in the same apparatus as that employed in 

 the evaporation of solutions of indican. After the evapora- 



was completed there was left a light brown syrup, ? 

 on being treated with alcohol was usually entirely dissolved. 

 The alcoholic solution was filtered if necessary, and then 



