70 ELEMENTARY AGRICULTURAL CHEMISTRY 



111 the above table it is assumed that the weight of soil to 

 a depth of four feet per acre is 16,000,000 lb. — i.e., that 

 each foot depth of soil per acre weighs 4,000,000 lb. 1 per 

 cent, of any constituent would thus correspond to 40,000 lb. 

 per acre in a depth of one foot, one-tenth per cent, to 4000 lb., 

 and so on. 



Sea water varies locally in composition, being affected by 

 the inllux of fresh water from large rivers, <tc., but far out 

 from land it is very constant in composition. The average 

 amount of total solid matter is about 3G grammes per litre, 

 or 2520 grains per gallon. Thorpe found as the constituents 

 of 1000 grammes of water of the Irish Sea, in 1870, the 

 following : — 



