COLOURING MATTERS IN WINE. 237 



colouring matter of wine when in contact with air, 

 than the possibility of extracting it pure from old, 

 red, crude tartar. 



In concluding, I must just make an observation 

 on a trace of tannate of iron salt which occurs in most 

 wines, and when only present in a very small quan- 

 tity, adds something to the colour of wine, but it can 

 by no means give the wine the colour of ink, since 

 tartaric acid decomposes tannate of iron, though less 

 readily than oxalic acid ; and free tartaric acid exists 

 in wine. 



