32 CHEMISTRY OF SOIL. 



Of phosphoric is 1 2, adding 2 oxygen =16 parts, 

 phosphoric acid is formed. 



Hence, the equivalents of these acids are, 40, 22, 

 28, numbers produced, by adding the proportions of 

 oxygen, to the respective bodies. These acids com- 

 bine, in their above equivalent proportions, with the 

 bases of silicates, forming neutral salts, or with two 

 or more proportions of acid form super-salts, or with 

 a larger portion of base, form sub-salts, and thus 

 form fixed and invariable compounds. Sulphate of 

 lime, is therefore in proportion of 28 of lime, to 40 

 of acid. Carbonate of lime, 28 to 22. Phosphate 

 of lime, 28 to 28, or neutral phosphate, or with a 

 larger proportion of lime, the phosphate of lime of 

 bones, or bone earth, so called ; and the equivalent 

 of each of these salts, is the number produced, by 

 adding that of the lime, to that of the acid. 



58. If sulphur, phosphorus, carbon, silicon, are 

 added to the metallic base of silicates, (45) the 

 combination is a uret — -the combination can take 

 place only in the equivalent proportions. It is thus 

 evident, that soil, consisting of silicates, urets, and 

 salts, is a fixed, unvarying, chemical combination of 

 these substances, though in proportions, somewhat 

 varied by local causes, yet presenting, in the mass, 

 a great identity of composition. The doctrine of 



