160 CHYMISTRY APPLIED TO AGRICULTURE. 



found in them, are not yet sufficiently developed to correct 

 the acid and disagreeable taste. 



The vegetable acids which are found most extensively 

 diffused in vegetables are the oxalic, citric, tartaric, ben- 

 zoic, gallic, acetic, malic, prussic, &C. The analysis of 

 vegetables presents a great number of acids, but as they 

 are found only in particular kinds of plants, and their 

 uses are either very limited, or altogether unknown, I do 

 not think it necesary to make here an enumeration of 

 them. 



Most acids are crystallizable, and some of them can be 

 -brought into a concrete state as soon as they are separated 

 from the other principles with which they are combined in 

 the plant. Vinegar, or the acetic acid, crystallizes when 

 highly concentrated ; M. Mollerat "prepared crystals of. it as 

 transparent as ice. 



Oxalic acid crystallizes in the form of four-sided prisms : 

 the acid of commerce presents this appearance. M. Deyeux 

 has found it free in the hulls of the chick pea, and it has 

 likewise been extracted from the expressed liquor of the 

 plant : it exists in the stalks and leaves of sorrel, and in the 

 juice of all the varieties of rhubarb. 



It may be produced by the action of nitric acid upon most 

 vegetable substances, especially sugar. 



Oxalic acid is soluble in water and alcohol ; cold water 

 dissolves one half of its own weight ; boiling water a 

 weight equal to its own ; and alcohol -^^jj of its own 

 weight. 



This acid possesses a strong affinity for the metallic ox- 

 ides, especially those of iron ; it has also the characteristic 

 property of depriving other acids of lime combined with 

 them, and of forming with it an insoluble salt ; and it is 

 upon these qualities that its use in the arts is principally 

 founded. 



Oxalic acid thrown into water containing any calcareous 

 salt, causes the liquor to become turbid, and forms from it a 

 deposit which is found to be the oxalate of lime. If the 

 oxalate of ammonia be made use of for the above purpose, 

 the action will be more speedy than if the oxalic acid be 

 used pure ; because decomposition is accelerated by the 

 exchange of principles constituting the two salts. 



The power which oxalic acid possesses of dissolving 

 readily the oxide of iron, renders it exceedingly useful in 

 the manufacture of stamped goods, especially of cotton 



