IEON IN WINE. 239 



justify this admirable sentence. But it is sufficient 

 to colour red wine, which contains very little free 

 tartaric acid so as to make it darker, and to give to 

 white wines, which contain tannic acid, a darker tinge 

 than tannic acid alone can produce. 



In Burgundy, which contains but little free tartaric 

 acid, the dark colour of the wine may, to a certain ex- 

 tent, be ascribed to the tannate of oxide of iron ; for if 

 a little tartaric acid be added to a diluted solution of 

 chloride of iron and tannic acid, it retains the black 

 colour. The wine being coloured by tannate of oxide 

 of iron or not, depends, therefore, entirely on the 

 quantity of free tartaric acid contained in it. 



"When red wine is mixed with a chalybeate water, 

 we generally ascribe the dark colour it assumes to the 

 ferruginous contents of the water ; but Bischof * has 

 justly contradicted this erroneous view. The car- 

 bonate of potass of the water saturates the free acid 

 of the wine, and so destroys the red colour ; but the 

 action of the alkali upon the colouring matter produces 

 a dirty hue, which becomes the more unsightly in pro- 

 portion to the preponderance of the alkali, and the 

 length of time during which it acts upon the colour- 

 ing matter (p. 218). 



* Tromsdorff N. Journ. Ed 13, st. 2, s. 321. 



