ACTION OF CARBONATES IN SOIL. 103 



loose, acts as such upon other silicates, and eliminates or 

 frees the alkaline bases. Let it be supposed that there is 

 clay, or silicate of potash and alumina in the soil. Let car- 

 bonate of lime, that is marble, or air-slacked lime, shells, 

 &c., be added to the soil. The result is, that slowly but 

 surely, chemical action takes place, the silicic acid pulling 

 one away and the carbonic acid another, the lime is changed 

 to silicate of lime, and the carbonic acid escapes, and now in 

 its turn acts upon silicates as did carbonic acid of air. The 

 alumina remains, the soil becomes more clayey. Thus sands 

 by liming are amended. 



134. This principle, of the action of carbonates, unravels 

 the agency of a vast variety of substances, which appear to 

 be very inert and inefficient. It must be remembered, that 

 the action of silicates and salts is alone under consideration, 

 uninfluenced by the presence of geine or plants. That action 

 in its simplest form constitutes the following, which may be 

 laid down as the ninth principle of agricultural chemistry, 



CARBONIC ACID, AND THE CARBONATES, DECOMPOSE THE 

 EARTHY, ALKALINE, AND METALLIC SILICATES OF SOIL. 



135. The result of this action is, that the potash, soda, 

 lime, magnesia, alumina, and metallic oxides are set free, 

 and where silicate of alumina exists, the soil becomes more 

 clayey, while the carbonic acid again acts upon silicates ot 

 alkalies and forms carbonates of alkalies. A clue is thus 

 given to the action of peat ashes, or coal ashes in amending 

 a sandy soil. These ashes act by their carbonate of lime as 

 above stated, freeing the alkali of the silicate of potash. 



136. Hitherto, the action of the inorganic elements has 

 been explained, uninfluenced by the organic or by geine. 

 Referring to the properties of this substance, it will be recol- 

 lected, that it is soluble or insoluble, that it combines with 

 alkalies, earths, and metals. It exerts a twofold action, 1st. 



