VEGETABLE ACIDS. ' 163 



This acid exists naturally in all wines, but it is more 

 abundant in those of the north than in those of the south ; 

 it predominates in them when made of unripe grapes, 

 or if the must have been badly fermented. White grapes 

 contain less malic acid than red ones, and I believe the 

 superiority of the liquor obtained from the first ought to 

 be referred to this difference. Brandy made from wine 

 abounding in this acid, turns vegetable blues red, and is 

 of a bad quality. Malic acid has not as yet been made use 

 of in the arts. 



Citric acid is found in large quantities in oranges- and 

 lemons, particularly in the last ; the skins of wild, hairy 

 plums, the red currant, cherries, strawberries, and rasp- 

 berries likewise contain it ; in these it is found united with 

 malic acid in nearly equal proportions. 



The process given us by Scheele for obtaining and 

 crystallizing citric acid, is the one we still make use of; the 

 acid is saturated with lime, and the insoluble salt thus formed 

 is decomposed by sulphuric acid diluted with water; the 

 liquor is then evaporated and the acid obtained in a crystal- 

 line form : by being repeatedly dissolved, filtrated, and 

 evaporated, the crystals are produced in the form of rhom- 

 boidal prisms, of which the inclined planes are terminated 

 at each end by a summit of four trapezoidal faces. 



In Sicily and some other countries where lemons grow in 

 profusion, it is customary to extract the juice of the fruit 

 and saturate it with lime; this citrate is afterwards sent to 

 the places where it is to be consumed, and there the opera- 

 tion of extracting the acid is terminated. The great quan- 

 tity of mucilage which the juice of the lemon contains, pre- 

 vents it from being kept for a long time, or conveyed to any 

 considerable distance, without undergoing changes that affect 

 its nature. 



The process of pressing the lemons is begun in November, 

 and ended in March : the quantity of juice extracted de- 

 pends on the ripeness of the fruit. The liquor is put into 

 barrels, and either sent off, or what is preferable, sold on the 

 spot to individuals engaged in manufacturing it into the 

 citrate of lime, in order to prevent the decomposition, which 

 exports of this nature always undergo. 



About -^ of carbonate of lime is required to saturate 

 a given weight of lemon juice : the citrate is carefully 

 washed, and after being dried is sent to its place of desti- 

 nation. 



