Dr. Schunck on the Formation of Indigo-llue. 33 



sulphuretted hydrogen is passed through the filtered liquid, by 

 the precipitated sulphuret of copper. A little more separates 

 occasionally in small white grains during the evaporation of the 

 liquid filtered from the sulphuret of copper, especially if the 

 temperature of the current of air passing over its surface be low, 

 as in winter. If, however, the residue left after evaporation of 

 the alcoholic extract be stirred up and agitated for some time 

 with water, so large a quantity of fatty matter becomes suspended 

 in the liquid as to render its separation without decomposi- 

 tion of the indican almost impossible, and it is for this reason 

 that I have found it advisable always to add water to the 

 alcoholic extract of the leaves before evaporation, and to pour off 

 the watery liquid from the undissolved chlorophyll and fatty 

 matter, instead of evaporating the extract by itself and then 

 stirring up the residue with water. 



I have very little to add to the description formerly given of 

 indican and its properties. It is always obtained in the form of 

 a transparent light brown syrup, and it cannot be separated from 

 the water which it still retains in this state without decompo- 

 sition. Its watery solution has a yellow colour and a purely 

 bitter taste. Even in the highest state of purity in which it can 

 be obtained, it produces when dissolved in water a slightly acid 

 reaction on litmus-paper. Whether this reaction is peculiar to 

 it, or whether it is a consequence of a commencing decomposition 

 of tliis easily decomposable substance, I am unable to decide. 

 After being prepared in the manner just described, it yields, when 

 subjected in small quantities to the action of acids, indigo-blue, 

 indirubiue and sugar, with mere traces of other products of de- 

 composition. When the same process, however, is performed on 

 a somewhat largeV scale, other products make their appearance 

 from causes which I shall j^resently explain. 



The new experiments which I have made to determine the 

 composition of indican, confirm the conclusions at which I arrived 

 in the first instance, and which are contained in the first part of 

 this paper. Being unable to obtain the substance itself in a 

 state fit for analysis, I was obliged, as before, to have recourse 

 to its compound with oxide of lead. This compound was pre- 

 ])ared in the following manner. Pure indican was dissolved in 

 cold alcohol, and the solution was mixed with a small quantity 

 of an alcoholic solution of acetate of lead and filtered from the 

 precipitate, which was generally of a somewhat dirty yellow 

 colour. On now adding to the li([uid an excess of acetate of 

 lead, a bright sulphur-yellow precipitate fell, which was collected 

 on a filter, washed with alcohol and then dried, at first in vacuo, 

 and tlicn for a few hours in the water-bath. Tiiis precipitate 

 was employed in the analyses I. and II. The liquid filtered 



Fhil. Mag. S. 4. Vol. 15. No. 07. Jan, 1858. D 



