224 COLOUBING MATTERS IN WINE. 



We learn, therefore, that this mixed colour, as it 

 exists in the liquid containing oxide of lead and acetic 

 acid, and in that containing alumina and acetic acid, 

 is neither free nor combined, but half-and-half; that 

 it divides or contends with acetic acid for the com- 

 bination with the base. Perhaps a double combina- 

 tion is formed of colouring matter, acetic acid and 

 alumina, or of colouring matter, acetic acid and oxide 

 of lead. The deportment of the half-blue, half- red 

 colour of the colouring matter of wine in these com- 

 binations, is exactly like that of one equivalent of 

 tartaric acid in cream of tartar, which retains its acid 

 reaction. 



I have dwelt upon these circumstances not so much 

 on account of their intrinsic value, as for two other 

 reasons. First, in order to recommend great caution 

 in using reagents for the sake of detecting adultera- 

 tions in red wine, since the least difference in genuine 

 wine, or in the reagent employed, may perceptibly 

 affect the colour ; and secondly, to see if in this way 

 we could obtain any more satisfactory explanation of 

 the peculiar colour of red wine. It follows from 

 what has been said, that the Hue colouring matter in 

 wine is chemically divided between tartaric or some 

 other free acid, and a substance which acts as a base ; 

 just as it is divided between acetic acid and alumina 

 in its violet colour in acetate of alumina. It does 

 not dissolve in tartaric acid with water or alcohol 

 with a pure wine colour, but red. If tannic acid be 



