COLOUEIKG MATTEES IN WINE. 223 



of wine ; in a dilute solution, like wine and water, 

 the violet colour is a little deeper. 



"When acetate of alumina is employed, no precipi- 

 tate is obtained from the liquid, which remains quite 

 clear, but the bright red hue of the colouring matter 

 of wine gives place to a violet shade. 



This circumstance is of great importance in the 

 theory of chemical affinities. It teaches us that the 

 blue colouring matter of the wine is half combined 

 with alumina and half with acid, that it is chemically 

 and yet not entirely combined. "We shall under- 

 stand what is here meant better if we remember what 

 was said p. 216, that sugar of lead in red wine yields 

 a pale dirty blue precipitate. Apothema is found in 

 it, and therefore it is no longer pure pale blue, and 

 the quantity of tartrate of lead present in it renders it 

 pale blue. Pure colouring matter combined with 

 pure oxide of lead yields a pure blue precipitate. 

 Hence, if the two ingredients be perfectly pure, the 

 compound will be blue. 



But a liquid containing acetic acid, and at the same 

 time acetate of lead, is obtained from the precipitate 

 of sugar of lead in red wine. Red colouring matter 

 is more or less soluble in acetic acid and water. 

 But when it flows from the precipitate, which acetate 

 of lead yields in red wine, it is not red but violet, a 

 mixture of red and blue. 



It is this same colour which remains dissolved with- 

 out "becoming turbid in acetate of alumina. 



