52 SOILS AND FERTILIZERS 



the pulverization and mixing of a great variety of 

 rock. 



52. Chemical Action of Water. — The chemical 

 action of water has not taken such an important 

 part in soil formation as the physical action. While 

 nearly all recks are practically insoluble in water 

 there is always some material dissolved, evidenced by 

 the fact that all spring-water contains dissolved 

 mineral matter. When charged with carbon dioxide 

 and other gases, water acts as a solvent upon rocks. 

 It converts many oxides, as ferrous oxide, into hy- 

 droxides. The chemical action of water may result in 

 the formation of new compounds more soluble or 

 readily disintegrated, as deposits of clay, which have 

 been produced by the chemical and physical action of 

 water upon feldspar rock. Limestone is quite readily 

 disintegrated by water, which produces many chemical 

 changes in both rocks and soils. The chemical action 

 of fertilizers known as fixation can take place only in 

 the presence of water. In fact water is necessary for 

 nearly all chemical reactions in the soil. 



53. Action of Air and Gases. — The part which air 

 has taken in soil formation has not been as prominent 

 as that taken by water. By the aid of oxygen, carbon 

 dioxide, and other gases and vapors in the air, rock 

 disintegration is hastened. The action of oxygen 

 changes the lower oxides to higher forms. All rock 

 contains more or less oxygen in chemical combination. 



