THK TREATMENT OF ALKALI. 37 



as humus, and forming with it, when dry, a black 

 compound, has given the name of black alkali lands to 

 those of which it is the principal saline constituent. 

 In time of drouth these can readily be distinguished 

 by the dark rings left on the margin of the dried-up 

 puddles. As Glauber's salt and common salt do not 

 possess this property, the soils impregnated with them 

 remain chiefly white and are known as white alkali 

 lands. 



Formation of Alkali Salts. — Alkali is a natural 

 element of the earth, the same as other minerals. 

 When the rocks on the mountains pulverize and the 

 sediments wash down on the plains, they bring the 

 alkali along and deposit it in the soil. The same 

 alkali salts are formed everywhere in the world, but 

 in countries having abundant rainfall they currently 

 wash through the soil into natural drainage, while in 

 regions where rainfall is deficient, the scant moisture 

 carries them down only a little way into the soil, from 

 which they rise to the surface by the evaporation of 

 water, and are thus accumulated at or near the top of 

 the soil. It is right there that nearly all the damage 

 is done. The water in the depths of the soil is rarely 

 strongly enough impregnated to hurt the roots of 

 plants diredlly. The alkali is all through the soil, but 

 is usually worse within a few inches of the surface. 

 It rises to the surface with each wetting of the ground, 

 in the same manner as a wick. Different wicks will 

 raise water or coal oil to different hights, according as 

 they are closely woven or loose, like candle wicking. 

 The close wick will raise the fluid higher in the end, 

 but it will raise to the highest point more slowly than 



