THE GBAPE. 43 



in water, sulphuretted hydrogen gas conducted through 

 it, the sulphide of lead filtered off, boiled with water, 

 and treated with alcohol and acetic acid, the liquid 

 then allowed to evaporate, and the residue freed from 

 fat by means of ether. 



By this process, the colouring matter of the purple 

 grapes is obtained pure. As it is also found in red 

 wine, we prefer- treating of it in detail later. Colour- 

 ing matter is more easily soluble in alcohol and tartaric 

 acid than in tartaric acid and water, and it is therefore 

 easily obtained from the skins by means of the juice, 

 which contains tartaric acid, and during the process 

 of fermentation, when the quantity of alcohol is con- 

 tinually on the increase. 



The colouring matter is blue, and the action of 

 acids makes it red. In unripe grapes, which are satu- 

 rated with acid, it is consequently red, and the riper 

 they grow, the more the diminution of the acid causes 

 it to become blue. The less acid the grapes contain, 

 the darker are the skins, and consequently the wine 

 extracted from the juice and skins is darker also. The 

 skins of very sweet grapes are often black. 



A considerable quantity of white wax may be ob- 

 tained from grape skins by means of boiling alcohol, 

 but this is of no particular importance to the wine. 

 The wax sinks when cold, and a still larger quantity 

 can be precipitated from the alcohol by the addition of 

 water. 



