342 ON THE SUGAR OF GRAPES. 



their acid in Scheele's mode, the juice of unripe grapo 



may be employed for the purpose with more advantage than 



has been supposed. 



This converted But the warmth of the weather promotes the maturity of 

 into sugar and , , . . . , . . . , , 



gum, th^s juice; the cjtric acid gradually disappears, so that 



scarcely any traces of it can be discovered in the ripe grape ; 

 and the products that occupy its place are the two species 

 of sugar mixed with a little gum. The elaboration of the 

 juice therefore consists in transforming this acid into gummy 

 and saccharine products, iu proportion as the fruit ap- 

 proaches maturity. 



The elements of the citric acid do not differ from those of 

 by parting with sugar and gum, as has been discovered ; but, since analysis 

 oxigen. -j^g^g found likewise, that it contains oxigen, or the acidify- 



ing principle, in more abundance than the nutritious pro- 

 ducts that assume its place, does this acid, during the 

 ripening, merely lose a part of its oxigen, so as to ap- 

 proach nearer their nature ? or does it raise itself to the 

 or acquiring same point by acquiring a larger proportion of carbon ? 

 car on. rpj^j^ admirable metamorphosis passes before our eyes every 



year, yet nature has covered it with a veil impenetrable to 

 them. To return to the fruit of the ripe grape. 

 Contents of the This juice, as it flows from the fruit in the press, con- 

 npe juice. tains substances of two kinds, some simply mixed, others 



in solution. The parts mixed are, first, the fibrous and 

 calcareous pulp, which composes the organization of the 

 berry ; and, secondly, a portion of the fetula, which we 

 call glutinous, on account of its resemblance to the animal- 

 ized substance of cheese termed gluten. 



These two substances, if diluted, may be separated by 

 the filtration of the juice, though imperfectly, on account 

 of its viscosity, and their tenaciousness, which choak up 

 the filter. But they may be separated much better by heat- 

 ing the juice to ebullition, because they coagulate, and rise 

 to the surface. When scummed, and strained through 

 flannel, the substances remaining dissolved in the clarified 

 juice are, 



1, A portion of fecula; 2, crystalHzable sugar; 3, sugar 

 not crystalHzable; 4, gum; 5, extractive matter, either 

 white, or tinged red, according to the species of grape. 



When 



