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XII On the Formation of Indigo-blue. Part II. 



By Edward Schunck, Ph.D., F.R.S. 



[Read April 1 5th, 1856.] 



In the first part of this memoir I announced the discovery 

 of a peculiar substance contained in the leaves of the Isatis 

 tinctoria, to which, as I there showed, the indigo-blue ob- 

 tained in the usual process of treating the plant owes its 

 origin. Having applied to this substance the name of 

 Indican, I proceeded to give a general account of its pro- 

 perties and of the process of decomposition which it under- 

 goes when subjected to the action of strong acids. I now 

 propose to present a more detailed account of the properties 

 of this substance and especially of the products of decom- 

 position derived from it. 



In continuing my experiments I soon arrived at the con- 

 clusion, that the different methods of preparing indican, of 

 which I had in the first part of this paper given a description, 

 though they sufficed for the preparation of small quantities, 

 were not well adapted for obtaining in a state of purity 

 the larger quantities of the substance which I found to be 

 necessary for the purposes of investigation. The great dif- 

 y in the preparation of indican arises, as i have before 

 stated, from the extreme facility with which it is decomposed, 

 when its solutions, especially the watery one, are heated, a 

 process of decomposition which is rapidly completed at a tem- 

 pttaturc a little below that of boiling water, and takes place 

 even at the ordinary temperature of the atmosphere, when 



i me. circumstance 



