216 COLOURING MATTEB3 IN WINE. 



This colouring matter is not a product of fermenta- 

 tion, nor is it in any way altered by fermentation ; it 

 exists in the skins of purple grapes, and may be ex- 

 tracted from them with precisely the same qualities 

 as from any kind of wine ; as has been already men- 

 tioned (p. 42). 



The manner in which I was most successful in pre- 

 paring pure blue colouring matter from Bordeaux wine 

 was as follows : 



The wine is precipitated by means of sugar of lead, 

 and the dirty pale blue deposit collected upon a filter. 

 As the liquid which passes through possesses an acid/ 

 reaction from acetic acid, it is pale violet. A little is 

 lost by washing; but when the liquid employed for 

 washing becomes neutral, what flows through becomes 

 colourless. This precipitate is suspended in water 

 through which sulphuretted hydrogen is then con- 

 ducted. The sulphide of lead is filtered off, and the 

 liquid, which then contains much tartaric acid, flows 

 through tolerably red, and it is so when washed with 

 water ; but when the liquid becomes neutral it remains 

 colourless. 



"Whether or no blue colouring matter be combined 

 with oxide of lead may be doubtful ; but it is certain 

 that it is not chemically combined with sulphide of 

 lead, it is held back by this in the same manner as by 

 animal charcoal. 



Eut this blue colouring matter is not entirely dis- 

 solved by boiling sulphide of lead with water. The 



