GEOLOGY OF SOIL. 87 



inch deep, and cut off the five right-hand figures; the 

 remainder is the number of pounds of that ingredient per 

 acre, at one inch deep. 



Let it be required to know how many pounds of salts of 

 lime are contained in eight inches deep of a soil which 

 weighs 126.6 pounds per cubic foot, and contains 2.047 of 

 salts of lime in 100 parts. 



43560 X 126.6 = 5514696 pounds per acre one fool deep. 

 5514696 -f- 12 = 459558 pounds " " one inch deep. 

 459558 X 2.047 = 940776636. 

 Cutting off five figures, leaves 9407 pounds at one inch deep. 

 8 



75258 ♦' al eight inches deep. 



It is to be remembered that this immense quantity is that 

 contained only in the finer portions of the soil ; there yet 

 remain about eighty parts in every hundred of soil as unde- 

 composed silicates, ready to yield their lime to the wants of 

 agriculture. 



Tried by the above rule, the smallest quantities which the 

 chemist obtains in his analysis become tons per acre, and 

 that which is too small to be weighed by any balance, the 

 " trace " only of an element rises to an amount which aston- 

 ishes by its magnitude. 



