DR. EDAVARD SCHUNCK ON INDIGO-BLUE. 225 



alcohol^ in order to remove the indifulvine and other re- 

 sinous substances. On treating the residue with boiling 

 alcohol^ the indirubine dissolves^ and is obtained^ after 

 several crystallizations, in the beautiful dark-red needles 

 characteristic of the substance. The portion insoluble in 

 boiling alcohol is indigo-blue, requiring for its purification 

 merely to be dissolved in some suitable menstruum, such as 

 boiling aniline. I am inclined to think that the same mole- 

 cular change takes place in the cells of the plant during the 

 later stages o£ its development ; for I obtained from some 

 leaves gathered late in the season when the flowers had begun 

 to appear, a quantity of indican having the usual appearance, 

 but giving, by decomposition with acid, far less indigo-blue 

 and more indirubine and other products than the indican 

 from younger leaves. This result was confirmed by expe- 

 riments, to be described presently, made with the leaves 

 themselves. 



The preceding experiments lead to the conclusion that 

 the leaves of Polygonum tinctorium contain a substance 

 not to be distinguished from the indican oflsatis tinctoria, 

 which, by decomposition with acids, yields indigo-blue and 

 glucose, accompanied by some by-products, and that there 

 is no proof of the existence of ready-formed colouring- 

 matter in the plant while the latter is living and in a 

 healthy state. The preexistence of indigo-blue, or of its 

 hydride, indigo- white, in these plants was taken for granted 

 forty or fifty years ago, when the class of bodies which we 

 now call glucosides and the peculiar kind of decomposition 

 which they undergo were unknown. Even now a superfi- 

 cial examination of some phenomena would almost cer- 

 tainly lead to the conclusion that the indigo-blue is formed 

 by the action of air, i. e. in consequence of the oxidation 

 of some easily oxidizable substance in the plant. Bearing 

 in mind, however, with what extreme facility indican is de- 



SER. III. VOL. VI. Q 



