CHEMISTRY OF SOIL. 31 



portions in which the elements of silicates combine, 

 it is found that the combining weight of 



Oxide of Manganese is 36. 



When any of these substances unite to an acid, 

 it is only in these proportions. The numbers are 

 equivalents — that is, 48 of potash are equal in satu- 

 rating power, to 32 of soda, or 28 of lime. All 

 equivalents, entering into the composition of soil, 

 contain the same quantity of oxygen. The com- 

 bining proportion of oxygen, is 8. Hence, if from 

 each of the above numbers, 8, the constant quantity, 

 is deducted, the remainder represents the equivalent 

 of the respective pure metals, which chemists rep- 

 resent by the termination in um, or ium ; and hence 

 are formed, potassium, sodium, &c. 



57. The equivalent of sulphur is 16, adding 3 

 oxygen =24 parts, sulphuric acid is formed. 



Of carbon is 6, adding 2 oxygen =16 parts, car- 

 bonic acid is formed. 



