220 COLOURING MATTEES IN WINE. 



this as a blue salt, and may be dissolved with a red 

 colour in acetic acid and alcohol. 



If a little more ammonia be added to the red solu- 

 tion of the colouring matter in alcohol and tartaric 

 acid, the colour, which a moment before was blue, 

 becomes green. If an acid be now added, the red 

 colour is restored, but is not so bright as before. If 

 the ammonia acts for a few moments, or if more be 

 added, it becomes brown. The green colour was a 

 mixture of blue and pale brown, which exhibits itself 

 as yellow. And an alteration had therefore already 

 occurred in the colouring matter. And if the con- 

 tinued operation of ammonia render it brown, the red 

 colour cannot again be restored to it by means of 

 acid. Hence ammonia decomposes the blue colouring 

 matter. 



This property, possessed in a still higher degree by 

 potash, soda, and lime, if added in excess, indicates 

 an alteration similar to that undergone by tannic acid, 

 grape sugar, and many other bodies. Quercitrin, a 

 yellow colouring matter, and many others, including 

 quercetin, which is prepared from quercitrin, are easily 

 changed by ammonia. * 



No satisfactory explanation of this fact can be 

 given ; we only know that the colouring matter of wine 

 may be easily decomposed by alkalies, and must con- 

 tent ourselves with this knowledge. 



At any rate we now understand why wines which 



* Kigaud in the Ann. des Pharm. Bd. 90, s. 283. 



