ABSORPTION OF GASES BY THE SOIL. 139 



growth of a plant. It is of consequence to the farmer 

 therefore that this oxygen should gain access to every part 

 of the soil and thus to the seed and the roots of the plants. 

 This easy acccess is of course facilitated artificially by the 

 perfect working of the land and making it as porous as pos- 

 sible. But there are some soils which absorb oxygen with 

 more rapidity and in larger quantity than others. Clays 

 absorb more oxygen than sandy soils : and vegetable soils 

 and peat more than clays. This is due in part to the natu- 

 ral porosity of the soil and in part to its chemical composi- 

 tion. Clay containing oxides of other minerals, for in- 

 stance, absorbs oxygen which enters into combination with 

 it, and decaying vegetable matter takes up much of it to 

 assist in its decomposition. 



These remarks all apply to the power and natural ten- 

 dency of soils to absorb carbonic acid from the atmosphere,, 

 together with the ammonia which rises from the earth from 

 decaying matter, and nitric acid which may be formed in 

 the air by electrical agency, and these contribute to some 

 valuable extent to the natural fertility of the land, but neces- 

 sarily in proportion to the power of absorption which is due 

 to its condition of porosity. Nothing more positive than this, 

 however can be asserted, because of the absence of satisfac- 

 tory experiments in this direction as to the relative capa- 

 bilities of soils to extract vegetable plant food from the at- 

 mosphere ; but one fact has been clearly ascertained, viz: 

 that all soils absorb gaseous substances of every kind most 

 readily and in the greatest abundance when they are in a 

 moist state. The rain fall, and the deposition of dew, as 

 well as the condensation of moisture in the soil from the at- 

 mosphere which circulates within it, will all, therefore, fa- 

 vor this absorption of fertilizing gaseous matter ; and this 

 will be greatest in those soils which naturally possess this 

 power in the greatest degree ; and when the artificial con- 

 dition of the soil, produced by thorough culture and pul- 

 verization, assists its natural proclivities most effectively. 



The pow r er of absorption of the suns heat is another ex- 

 ceedingly important property of soils and this also varies 



