118 ACTION OF SALTS. 



the liberated alkali, acting on the geine. Its perma- 

 ment effects, for experience has proved permanency 

 of effect, peculiarly 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 ma- 

 nure, while the condensed oxygen acts slowly on 

 the geine, forming carbonic acid. It has upon' 

 the geine, buried in the soil, the same effect that til- 

 lage would have, rendering it soluble, with this addi- 

 tional advantage — that its carbonic acid instead of 

 escaping acts on the silicates. New portions of al- 

 kali are thus liberated, supplying for years that which 

 was first applied, as a part of the saltpetre. The ni- 

 trates then, hold the very first place among salts, 

 in agriculture. 



169. Thirdly, phosphates — this includes bones, 

 horn, hair, nails, hoofs, and claws, and a large portion 

 of the salts found in the liquid excretions of animals. 

 These act much like nitre, the acid forming a con- 

 stituent 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 



