340 PHYSIOLOGY AT THE FARM. 



grapes. During the fermentation of the juice of the grape, the 

 bitartrate of potassa, combined with colouring and extractive 

 matters, becomes deposited on the sides of the cask, whence 

 it is collected under the name of crude tartar, argol, or wine- 

 stone. 



When wine is kept long in bottle a farther deposition of the 

 same material occurs, known then as the crust. 



The formula for tartaric acid in the anhydrous state is 

 C 4 H 2 5 . 



Malic Acid, or the Acid of Apples. The malic acid exists 

 largely throughout the vegetable kingdom. It exists free in 

 apples, pears, quinces, plums, apricots, peaches, cherries, 

 gooseberries, currants, strawberries, raspberries, brambleber- 

 ries, pine-apples, barberries, elderberries, grapes, love-apples 

 (tomatoes), tamarinds, and some other fruits. Most commonly 

 citric acid accompanies malic acid. Malic acid is contained in 

 wine, cider, and perry. Its formula is C 8 H 4 3 + water 2 . In 

 its effects on the living body it appears to be analogous to citric 

 acid ; but it is not employed in the separate state. 



Oxalic Acid. Oxalic acid is found in a considerable number 

 of plants. It exists in the garden rhubarbs, the leaf-stalks of 

 which have been of late years so much employed in tarts and 

 puddings. In these plants, besides the free oxalic acid, there 

 is oxalate of lime, which probably renders the over free use of 

 the leaf-stalks of rhubarb unsafe in constitutions in which there 

 is a tendency to the deposition of mulberry calculus in the 

 urinary passages. In short, the very free use of rhubarbs in diet 

 is not of long enough standing to enable a cautious reasoner 

 to determine its true value as an article of food. The leaf- 

 stalks of rhubarbs were used occasionally in the last century, 

 both in France and in this country, in marmalades and tarts ; 

 but it is not more than thirty or forty years since the use of 

 them became general throughout the United Kingdom. 



