48 CHEMISTRY OF SOIL. 



8 oxygen, 24 sodium = 32 soda, 



8 " 28 iron == 36 oxide of iron, 



8 *' 28 manganese ==» 36 oxide of manganese. 

 When any of these oxidated substances unite to an acid, it 

 is only in these proportions. The numbers are equivalents 

 — that is, 48 of potash are equal in saturating power, to 32 

 of soda, or 28 of lime. All equivalents, entering into the 

 composition of soil, contain the same quantity of oxygen. 

 Hence, if from each )f the above numbers in the third 

 column, 8, the constant quantity, is deducted, the remainder 

 represents the equivalent of the respective pure metals, 

 which chemists represent by the termination in um or iiim; 

 and hence are formed, potassium, sodium, &c. (40), (41). 



57. The equivalent of sulphur is 16, adding 3 oxygen =» 

 24 parts, sulphuric acid is formed == 40. 



The equivalent of phosphorus is 32, adding 5 oxygen = 

 40 parts, phosphoric acid is formed. The equivalent of car- 

 bon is 6, adding 2 oxygen =^ 16 parts, carbonic acid is 

 formed. 



Hence, the equi^/alents of these acids are 40, 72, 22, num- 

 bers produced by adding the proportions of oxygen to the 

 respective bodies. These acids combine, 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 of lime to 22 of acid. Phosphate of 

 lime has a larger proportion of base, 3 parts or 84 of lime 

 to 72 of acid ; this is bone earth, so called ; and the equiva- 

 lent of each of these salts is the number produced, by add- 

 ing that of the lime to that of the acid. 



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



