Dr. Schunck on the Formation of Indigo-blue. 35 



629 100-00 647 100-00 



The first analyses which I made of the lead compounds of 

 indiean, the results of which are recorded in the first part of 

 this paper, led to the formulas C^^ H^s NO^^ and C^^ H^^ NO^", 

 but I stated at the same time that neither of these could be con- 

 sidered as the true formula, since the compounds then analysed 

 seemed no longer to contain unchanged indicau. However, the 

 compounds, the analyses of which have just been given, even 

 after having been completely dried and decomposed with cold 

 dilute sulphuric acid, yielded solutions which, after having been 

 filtered from the sulphate of lead and boiled, deposited flocks 

 consisting almost entirely of indigo-blue and indirubine, pro- 

 ducts indicating with certainty the presence of unchanged indi- 

 can. Since indican exhibits a tendency, as I have before observed, 

 to take up successively a number of equivalents of water, it is 

 probable that of the two formulas given above, the first, viz. 

 C^^ H^' NO*', approaches nearest to, if it is not a correct repre- 

 sentation of, its true composition. The formula C^^ jjss ]n^ O^^ 

 may then represent a mixture of indican with a small quantity 

 of what may be called its hydrate, or it may show the composi- 

 tion of indican in the first stage of its hydration before it has 

 lost the property of yielding indigo-blue by decomposition. As 

 far as regards the explanation of the diff"erent processes of 

 decomposition which the substance undergoes, it is of course 

 immaterial which formula is adopted. 



Action of Acids on Indican. 



In the first part of this memoir I have given a general de- 

 scription of the process of decomposition which indican under- 

 goes by the action of acids, and of the products thereby formed. 

 I shall now proceed to give an account of the results obtained 

 in a more minute investigation of this process, performed with 

 larger quantities of material than had previously been at my 

 disposal. 



Sulphuric and muriatic acids are not the only acids capable of 

 effecting the deconqjosition of indican. If to a watery solution 

 of the latter, a small quantity of nitric acid be added, the quan- 

 tity of the acid not being large enough to enable it to exert 

 any oxidizing action on the indican, the solution immediately 

 becomes grecji and turbid, and on standuig it deposits Hocks of 



D2 



