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



precipitates with the chlorides of barium and calcium and with 

 nitrate of silver, while the liquid in each case becomes colourless. 

 The alcoholic solution gives with acetate of lead a brown preci- 

 pitate, which dissolves entirely on the addition of acetic acid ; 

 and with acetate of copper it gives a slight brown precipitate, the 

 filtered liquid being still dark brown. 



In the first part of this paper I have given for indiretine the 

 formula C^^ H^'^ NO^^. The analyses which I have made Avith 

 fresh preparations of this body lead to the formula C^ H^^ N0'°, 

 as will be seen from the following details. 



I. 0-3955 grm., dried at 100'^ C. and burnt with oxide of cop- 

 per and chlorate of potash, gave 0-9565 grm. carbonic acid and 

 0-1995 water. 



0-5315 grm., burnt with soda-lime, gave 0-1400 grm. platinum. 



II. 0-4250 grm. of the same preparation, heated to 190° C. 

 and then kept for several hours at 100° C, gave 1-0300 grm. 

 carbonic acid and 0-2090 water. 



0-5065 grm. gave 0-1370 grm. platinum. 



III. 0-4210 grm. of a different preparation gave 1-0200 grm. 

 carbonic acid and 0-2140 water. 



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 diflFer from one another merely by 3H0, pro- 

 ceeds from any impurity in either case, or that it is to be attri- 

 buted 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 investiga- 

 tion of this series, of a body exhibiting when prepared on dif- 

 ferent 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 solu- 

 ble 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 

 was separated by filtration ; the sulphuric acid was removed by 



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