PHYSICAL PROPERTIES OP SOIL. 223 



changed. They do not combine with it. They 

 merely induce on the absorbed moisture, power to 

 imbibe oxygen. But when geine absorbs oxygen, 

 one portion of that combines with its carbon, produ- 

 cing carbonic acid, which decomposes silicates, and 

 a second portion of oxygen combines with the hydro- 

 gen of the geine, and produces water. Hence, in a 

 dry season well manured soils or those abounding in 

 geine, suffer very little. The power of geine to pro- 

 duce water, is a circumstance of soil almost wholly 

 overlooked. It is one, whose high value will appear 

 by a comparison with the quantity of water, produced 

 by a fresh ploughed, upturned sward, with that from 

 the same soil undisturbed. The evaporation from an 

 acre of fresh ploughed land is equal to 950 lbs. 

 per hour ; this is the greatest for the first and second 

 days, ceases about the fifth day, and again begins by 

 hoeing, while at the same time the unbroken sod 

 affords no trace of moisture. This evaporation is 

 equal to that which follows after copious rains. 

 These are highly practical facts, and teach the ne- 

 cessity of frequent stirring of soil in a dry time. 

 Where manure or geine is lying in the soil, the evap- 

 oration is from an acre, equal to 5000 lbs. per hour. 

 At 2000 lbs. of water per hour, the evaporation would 

 amount in 92 days to 2,208,000 lbs. which is nearly 



