FOEMATION OF INDIGO-BL. 187 



composition of the indican almost impossible, and it is for 

 eason 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 decomposition. 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 this 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, indirubine and 

 sugar, with mere traces of other products of decomposition. 

 When the same process however is performed on a somewhat 

 larger scale, other products make their appearance from causes 

 which I shall presently 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 com- 

 l was prepared in the following manner. Pure indican 

 was dissolved in cold alcohol, and the solution was ir. 

 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 

 d an excess of acetate of lead a bright sulphur-yellow 



