366 ODOEOGEAPHIA. 



Liebig observed that grapes grown in hot climates and the 

 boiled juice obtained from them, are proportionately rich in sugar. 

 Hence, during the fermentation of the juice, the complete 

 decomposition of its nitrogenised matters, and their separation in 

 the insoluble state, are effected before all the sugar has been 

 converted into alcohol and carbonic acid. A certain quantity of 

 the sugar consequently remains mixed with the wine in an 

 undecomposed state, the condition necessary for its further 

 development being absent. The nitrogenous matters in the juice 

 of grapes of the temperate zones, on the contrary, are not 

 completely separated in the unsoluble state when the entire 

 transformation of the sugar is effected. The wine of these grapes, 

 therefore, does not contain sugar, but variable quantities of 

 undecomposed gluten in solution. This gluten gives the wine the 

 proijerty of becoming spontaneously converted into vinegar when 

 the access of air is not prevented : for it absorbs oxygen and 

 becomes insoluble, and its oxidation is communicated to the alcohol, 

 which is converted into acetic acid. By allowing the wine to 

 remain at rest in casks with a very limited access of air, and at 

 the lowest possible temperature, the oxidation of this nitrogenous 

 matter is effected without the alcohol undergoing the same change, 

 a higher temperature being necessary to enable alcohol to combine 

 with oxygen. As long as the wine in the " stilling casks " deposits 

 yeast, it can still be caused to ferment by the addition of sugar, 

 but old, well-cleared wine has lost this property, because the 

 condition necessary for fermentation, viz., a substance in the act of 

 decomposition or putrefaction, is no longer present in it. In hotels 

 and other places where wine containing much gluten is drawn 

 gradually from a cask, and a proportional quantity of air 

 neces.sarily introduced, its eremacausis (conversion into acetic 

 acid), is prevented by the addition of a small quantity of sulphuric 

 acid. This acid, by entering into combination with the oxygen of 

 the air contained in the cask or dissolved in the wine, prevents 

 the oxidation of the organic matter. 



■ Cognac Essence/' " Oilof Cofjnac" or commercial (Enanthic 

 ether. This article is produced on a large scale by distilling wine- 

 lees, either dried and pressed into cakes, or in their wet state, 

 mixed with 7 or 8 times their weight of water : the distillation 

 jjeing effected by passing a current of dry steam through tlie mix- 



