208 MR. E. SCHUNCK ON THE, &c. 



my intention to continue them. The action of acids on 

 indican requires still further examination, and the effects 

 produced by ferments and other agents remain to be inves- 

 tigated. I also propose to examine other indigo-bearing 

 plants, in order to ascertain whether they contain indican 

 or not. 



The results of the present investigation may be summed 

 up in the following propositions : — 



1. The Isatis tinctoria does not contain indigo-blue ready 

 formed, either in the blue or colourless state. 



2. The formation of the blue colouring matter in watery 

 extracts of the plant is neither caused, nor promoted by, the 

 action of oxygen or of alkalies. 



3. Indigo-blue cannot be said to exist in any state of 

 combination in the juices of the plant, it is merely con- 

 tained in them potentially. 



