EAIN. 91 



contains one-half more oxygen, and four times the 

 amount of carbonic acid which is found in the 

 atmosphere through which it falls. The Cyclopedia 

 of Agriculture remarks : " Rain-water always con- 

 tains in solution air, carbonic acid, and ammonia. 

 The first two ingredients are among the most power- 

 ful disintegrators of a soil. 



" The oxygen of the air and the carbonic acid, 

 being both in a highly condensed form by being 

 dissolved, possess very strong affinities for the in- 

 gredients of the soil. The oxygen attacks and 

 oxidizes the iron; the carbonic acid, seizing the 

 lime and potash, and other alkaline ingredients of 

 the soil, produces a further disintegration, and 

 renders available the locked-up resources of this 

 magazine of nutriment. 



" Before these can be used by plants, they must 

 be rendered soluble ; and this is only effected by 

 the free and frequent access of rain and air. The 

 ready passage of both of these, therefore, enables 

 the soil to yield up its concealed treasures." 



The amount of ammonia contained in the rain-fall 

 of a year upon a single acre is equivalent to the 

 amount found in from one to two hundred weight 

 of Peruvian guano. To retain this in the soil, it is 

 obvious that the water in which it is contained must 

 percolate through its particles. This it cannot do 

 if the land is already overcharged with moisture, as 

 is the case in most of our soils. When it cannot 



