VEGETABLE ACIDS. 117 



The vegetable principles are divided by Thompson into 

 the four following classes. 



I. Acids. 11. Alkalies. III. Intermediate bodies. IV. 

 Neutral bodies. 



The substances, classed under these heads, are not all the 

 products of the vital principle. Some of them result from de- 

 compositions, and hence are the products of death rather than 

 of life.* A large number of the products of vitality are in- 

 serted in this section as a convenient reference for those who 

 have not better sources of information. The agricultural 

 reader can omit them, if he chooses, altogether. 



I. Acids. The number of acids, derived from the vegetable 

 kingdom, amount to 116, but a few of this number are of any 

 particular impoitance to agriculture. The following are the 

 principal vegetable acids. Oxalic, citric, tartaric, benzoic, me- 

 conic, acetic, malic and prussic acids. All, save the last three 

 which have been obtained only in a liquid state, are white crys- 

 taline solids. All are more or less soluble in water. All are 

 sour to the taste, with the exception of gallic and Prussic acids, 

 the first of which being astringent, and the latter having the 

 taste of bitter almonds. 



1. Oxalic acid (€^03=36.24)1 is found in wood sorrel, [Oxalis 

 acetosella,) and is the cause of its sour taste. It also exudes from 

 the chic pea [deer arietinum). Many vegetable principles, such 

 as gum, starch, etc. are converted into this acid by nitric acid. 

 It exists in small, slender crystals, resembling epsom salts, for 

 which it is sometimes mistaken with fatal consequences. It is 

 a powerful poison with a strong acid taste. It is distinguished 

 by its power of decomposing all salts of lime, and forming with 

 the base an insoluble salt. This acid is found in combination 

 with lime [Oxalate of lime) in several species of lichens. When 



* For a complete description of all the vegetable principles, the rea- 

 der is referred to Thompson's Chemistry of Organic Vegetable Bodies. 



=1 The expression, 020^=36, when translated, would read thus : 

 Oxalic acid is composed of 2 equivalents of carbon, or 12.24 parts by 

 weight, and 3 equivalents of oxygen, or 24 parts by weight, which 

 makes an equivalent of oxalic acid equal to 36.24 ; that is, when oxalic 

 acid combines with any other body, it always unites 36 parts by weight. 



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