ANALYSIS OF WINE. 343 



rise to a voluminous precipitate, which when further 

 evaporated is resolved into apo-glucic acid. 



If therefore the object be to obtain the sugar, and not 

 to form from it glucic acid, evaporation must not be 

 employed. Knowing how very easily the sugar exist- 

 ing in red wine is resolved into glucic acid, I have 

 carefully sought for this acid, but in vain. I think 

 it probable that the small quantity of brown sub- 

 stance found in the liquid obtained from the pre- 

 cipitate of sugar of lead and basic acetate of lead, 

 contains apo-glucic acid (p. 253). 



If glucic acid be contained in wine, it escapes 

 analysis by resolving itself into apo-glucic acid, even 

 when it is precipitated with lead salts. It is well 

 known that glucate when exposed to the air is speedily 

 transformed into apo-glucate. Here, where only a 

 little exists, the transformation must be very rapid. 

 Not only the precipitate of sugar of lead, but likewise 

 that obtained from basic acetate of lead and ammonia 

 become darker when exposed to the air. 



"What Scheele calls " extractive matter," contains, 

 after becoming brown, apo-glucic acid ; it is a pro- 

 duct of sugar which first passes into glucic acid, 

 and when exposed to the air becomes brown and 

 decomposed. 



4. The liquid obtained after the separation of the 

 precipitates with sugar of lead, and basic acetate of lead 

 and ammonia, was freed from lead by sulphuric acid. 

 Potash, soda, lime, and magnesia might exist in it, 



