SOLUBLE PHOSPHORIC ACID. 187 



tinct processes, but the chemical operation of 

 each is precisely the same ; it is simply a union 

 of the carbon contained in the dead vegetable or 

 animal matter, with the oxygen of the atmos- 

 phere, or the oxygen of the water present in the 

 substance. This chemical union of oxygen and 

 carbon produces carbonic acid gas, the properties 

 of which have been fully explained. The 

 action of this gas' on the silicate of potash, 

 separates the potash from the silica and forms 

 carbonate of potash, the silica being liberated, 

 as hydrated silica. This change renders both 

 substances immediately available, as food for 

 plants. Before the change, they were in an 

 insoluble condition, and, if contained in unrotted 

 straw, might remain in the soil a year or more, 

 without benefiting growing vegetation. As the 

 phosphate of lime contained in plants is in the 

 most finely divided state, the carbonic acid 

 attacks and decomposes this compound, forming 

 carbonate of lime, and liberating the phosphoric 

 acid in a soluble condition, for the use of the 

 plant. 



There is a remarkable chemical law, namely : 

 that some elements have no affinity for each 

 other, and hence will not form compounds unless 

 one or tlie other is present in what is termed the 

 nascent state., that is, the state in which it ex- 

 ists at the moment it is separated from a pre- 







