20 SOILS: PROPERTIES AND MANAGEMENT 



carbon dioxide (C0 2 ), which is universally a constituent 

 of air and is a product of the decaying vegetable matter 

 present in most soils. This means that the water cir- 

 culating among rock fragments, especially those of a soil, 

 is heavily charged with this compound. The carbon a- 

 tion may be illustrated as follows : — 



2 FeS 2 + 7 2 + 4 H 2 + 2 C0 2 = 2 FeC0 3 + 4 H 2 S0 4 or 

 2 NaOH + C0 2 = Na 2 C0 3 + H 2 



17. Deoxidation. — Deoxidation is an opposite re- 

 action to oxidation, being a loss of oxygen either to the 

 air or to some other compound. With hematite it might 

 take place as follows : — 



2 Fe 2 3 - 2 = 4 FeO 



Under normal conditions, however, it is. not a very im- 

 portant factor, since most rock fragments and soil are 

 fairly well aerated, at least too well aerated to allow this 

 reverse process to occur. In poorly drained soil or in 

 soil very rich in humus and carrying organic acids it 

 may occur, and is usually manifested by the development 

 of blue and gray colors, indicating that a reduction has 

 taken place. The bleaching of sands, sandstones, and 

 clays may be due partially to this, and also to a removal 

 of the ferriferous salts in solution. Some subsoils dis- 

 play this phenomenon. The average farmer, however, 

 need not concern himself with the injuries that may re- 

 sult from deoxidation. 



18. Hydration. — Hydration usually accompanies oxi- 

 dation, but when occurring at great depths it may be 

 practically the only change the minerals have imdergone. 

 Minerals, especially feldspars, become clouded and lose 

 their luster on this assumption of chemically combined 



