COLOURING MATTERS IN WINE. 219 



colouring matter when combined with an acid, by 

 means of the solution in alcohol and tartaric acid. In 

 a perfectly pure state it is perfectly soluble in alcohol 

 and tartaric acid, though only in small quantities, and 

 yet, after being dried, it required some hours to dis- 

 solve. It then yielded a singularly beautiful red 

 tincture, and thus we may study its deportment in the 

 circumstances in which it is found in wine. It is then 

 red, not wine-coloured. 



It is insoluble in ether combined with tartaric acid, 

 as also in chloroform and sulphide of carbon. If 

 therefore the solution in tartaric acid be agitated with 

 one of these three liquids, they remain colourless. 



If any dilute ammonia be added to the solution in 

 alcohol and tartaric acid, it will, after complete satura- 

 tion, become blue ; if too little be added, it exhibits the 

 above-mentioned colour of chrome alum. 



The blue colour is likewise attainable by adding, 

 with the greatest caution, potash, soda, or lime-water ; 

 and the addition of an acid will restore the colour. 



As the blue precipitate is obtained by means of 

 basic acetate of lead, and sugar of lead, we have here 

 a chemical compound to deal with. The oxide of lead 

 supplants the acid which made the blue colouring 

 matter red. The colouring matter of wine, which is 

 pure blue, forms a blue compound with oxide of lead. 



And thus the colouring matter is a body capable of 

 replacing a base or an acid ; it displaces the acetic acid, 

 which had combined with oxide of lead, unites with 



