Natural Waters. 



77 



Different crops are possessed of different resisting powers to 

 these salts. As a rule sodium carbonate is the most effective in 

 causing injury to plants and sodium sulphate the least. For- 

 tunately, however, " black alkali" i. e., sodium carbonate can 

 be rendered almost harmless by the application of gypstim to the 

 soil, which decomposes the sodium carbonate with formation of 

 the very much less harmful substances, sodium sulphate and 

 calcium carbonate. If "white alkali" is due to common salt, it 

 cannot be cured except by drainage. 



According to results accumulated in this country, and tabu- 

 lated by Ingle, the following figures give the highest proportion 

 of sodium chloride, sodium sulphate and sodium carbonate which 

 may be present in soils without injury to the plants named. The 

 figures represent the amounts in pounds of the various constit- 

 uents present in the upper four feet of soil per acre : 



In this table it is assumed that the weight of soil to a depth 

 of four feet per acre is 16,000,000 pounds, or that each acre-foot 

 of soil weighs 4,000,000 pounds. One per cent of any constituent 

 would then correspond to 40,000 pounds per acre to a depth of 

 one foot, one-tenth per cent to 4,000 pounds, and so on. 



