222 PHYSICAL PROPERTIES OF SOIL. 



clay, loam, sandy clay, arable soil. They all satu- 

 rate themselves with moisture by a few days' expos- 

 ure. It is a very interesting question, does soil 

 give up this absorbed water speedily and equally ? 

 Is its power of retaining water equal ? As a gen- 

 eral fact, it may be stated, that the soil which ab- 

 sorbs fastest and most, evaporates slowest and least. 

 Geine evaporates least in a given time. The pow- 

 er of evaporation, is modified by the consistence of 

 soil ; by a different degree of looseness or compact- 

 ness of soil. Garden mould, for instance, dries 

 faster than clay. As it has been already shown, that 

 the power of being warmed is much modified by 

 moisture, so the power of a soil to retain water, 

 makes the distinction of a hot or cold, wet or dry 

 soil. In all the relations to moisture, as to heat, 

 geine exercises the greatest influence. 



295. Connected with this power of absorption of 

 moisture, is the very important relation of soil to gas. 

 All soil absorbs oxygen gas, when damp, never when 

 dry. Of the ingredients of soil, geine forms the^only 

 exception to this rule. That absorbs oxygen, whether 

 it be wet or dry. Geine has this power in the high- 

 est degree, clay next; frozen earths not at all. A 

 moderate temperature increases the absorption. 



When earths absorb oxygen, they give it up un- 



