ACTION OF CARBONATES IN SOIL. 89 



bonic 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 mysterious action of a vast variety of 

 substances, which appear to be very inert and inef- 

 ficient. It must be remembered, that the action of 

 silicates and salts is alone under consideration, uninflu- 

 enced by the presence of geine or plants. That ac- 

 tion in its simplest form constitutes the following which 

 may be laid down as the ninth principle of agricul- 

 tural chemistry. Carbonic acid, and the car- 

 bonates, DECOMPOSE THE EARTHY, ALKALINE, AND 

 METALLIC SILICATES OF SOIL. 



135. The result 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 of 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, free- 

 ing the alkali of the silicate of potash. 



136. Hitherto, the action of the inorganic ele- 



8* 



