188 MK. E. SCHUNCK ON THE 



copper-coloured by reflected light. If instead of adding acid 

 to any of the solutions yielding indigo-blue, caustic soda 

 was first added in excess and the solution was left for a few 

 moments, and then boiled with an excess of acid, it merely 

 became brown without depositing any indigo-blue. Having 

 taken some finely chopped woad leaves, I pounded them in 

 a mortar'with cold alcohol. On filtering I obtained a clear 

 green solution, leaving on evaporation at a gentle heat a 

 green syrup, from which on the addition of water a quantity 

 of chlorophyll and fatty matter separated in drops. The 

 watery solution, which after filtration had only a yellowish 

 tinge, on being boiled with the addition of sulphuric acid 

 deposited a quantity of purple flocks, which were treated, 

 after filtration and washing with water, with successive por- 

 tions of boiling alcohol. The first portions of the alcohol 

 with which they were treated acquired a beautiful purple 

 colour, and the last portions a pure blue, each portion de- 

 positing on standing some flocks of a fine blue colour. The 

 green mass insoluble in water contained no indigo-blue. 

 Having carefully dried a few woad leaves, I reduced them 

 to powder and then treated them in a bottle with cold ether, 

 I obtained a dark green solution, which after being filtered 

 and evaporated spontaneously left a green syrupy residue, 

 from which water extracted as in the preceding case a sub- 

 stance, which by the action of boiling sulphuric acid yielded 

 an abundance of very pure indigo-blue. 



By these and similar simple and easily performed experi- 

 ments, I was enabled to infer, with positive certainty, that 

 the Isatis tinctoria contains a substance easily soluble in 

 hot and cold water, alcohol, and ether, which, by the action 

 of strong mineral acids, yields indigo-blue; that the forma- 

 tion of the colouring matter from it can be eifected without 

 the intervention of oxygen or of alkalies, and that the latter, 

 indeed, if allowed to act on it before the application of acid, 

 entirely prevent the formation of colouring matter, and it 



