196 WALL'S MANUAL 



When oxydized substances combine with an acid, 

 it is only in these proportions. The numbers are 

 called equivalents ; that is, 47 of potash is equal in 

 saturating power to 31 of soda, or 28 of lime, 



The equivalent of sulphur is 16, adding 3 equiva- 

 lents of oxygen or 24, wo have 40, or the equivalent 

 of sulphuric acid. The equivalent of phosphorus 

 is 32, adding 5 equivalents of oxygen, we have 

 40x32 72 phosphoric acid. The equivalent of 

 carbon is 6x16, or 2 of oxygen =s 22 carbonic acid. 

 Hence, the equivalents of the acids are 40, 72, 22. 

 These acids combine with bases in the above pro- 

 portions, forming neutral salts, or with two or more 

 proportions of acid, forming super-salts, or with a still 

 larger proportion base, forming sub- salts ; thus, 

 are formed sulphate of lime or plaster, 28 lime x40 

 sulphuric acid. Carbonate of lime, 28 lime x22 

 carbonic acid. Phosphate of lime has a larger 

 proportion of base, 3 parts or 84 of lime x72 

 phosphoric acid. 



When the subject of the composition of the soil is 

 discussed, the value of this slight knowledge of 

 chemical rotation and combining proportions is 

 manifest. 



SIMPLE MINERALS. 



Yiewed by the light of chemistry, rocks are mostly 

 masses of silicates. The simple minerals composing 

 most rocks are truly, only silicates in fixed proportions. 

 The simple minerals are quartz, feldspar, mica, horn- 

 blende, augite, talc. In each mineral, the t base is 

 combined with silica, which acts as an acid, a com- 

 pound or silicate is formed. 



