ACTION OF SALTS. 127 



alkalies. The immediate effects are due to the liberated 

 alkali, acting on the geine. Its permanent effect, for experi- 

 ence has proved permanency of effect, due to nitrates, is 

 owing to the liberation of an immense dose of oxygen which 

 is produced from the gradual decomposition of the acid. 

 Now, the insoluble geine condenses this in its pores, like 

 charcoal. This condensation, like that of gas by charcoal, 

 produces heat ; it is like fermenting manure, while the con- 

 densed oxygen acts slowly on the geine, and forms carbonic 

 acid. It has upon the geine, buried in the soil, the same 

 effect that tillage would have, rendering it soluble, with this 

 additional advantage, that its carbonic acid, instead of es- 

 caping, acts on the silicates. New portions of alkali are 

 thus liberated, supplying for years that which was first 

 applied as a part of saltpetre. The nitrates, then, hold the 

 very first place among salts in agriculture. 



169. The third class (c. 158) of the nourishers are the 

 phosphates. This class includes bones, horns, nails, hoofs, 

 claws, and a large portion of the salts found in the liquid 

 excretions of animals. These act much like nitre, the acid 

 forming a constituent of the plants. It is not probable that 

 the acid in this class is decomposed. It has not yet been 

 proved that carbonates and nitrates exist, already formed, 

 except in a very few plants. The quantity of salts which 

 may be applied, will be greater for the carbonates, less for 

 the nitrates, and least for the phosphates. The quantity of 

 any salt which may be used, will, after the largest amount 

 which can be safely employed has been ascertained, depend 

 upon the farmer's ability to produce it. Carbonate of lime 

 may be used to any extent, according to the farmer's idea 

 of its value. Carbonates of alkali may be used with benefit. 

 The largest quantity which has been known to be used with- 

 out injury, has been 53 bushels of ashes per acre, which are 



