190 SOILS AND FERTILIZERS 



phate being first deposited, then a layer of rock salt, 

 and finally layers of potash and magnesium salts in 

 the order of their solubility. 



234. Kainit is a mineral composed of potassium 

 sulphate, magnesium sulphate, magnesium chloride, 

 and water of crystallization. As it comes from the 

 mine it is mixed with gypsum, salt, potassium chlo- 

 ride, and other bodies. Kainit contains from 1 2 to 1 2. 50 

 per cent, of potash, and is one of the most important 

 of the Stassfurt salts. It is extensively used as a pot- 

 ash fertilizer, and is also mixed with other materials 

 and sold as a commercial fertilizer. The magnesium 

 chloride causes it to absorb water, and the presence of 

 other compounds results in the formation of hard 

 lumps, whenever kainit is kept for a long time. 

 Kainit is soluble in water, and can be • used as a top 

 dressing at the rate of 75 to 200 pounds or more per acre. 



235. Sulphate of Potash. — High-grade sulphate 

 of potash is prepared from some of the crude Stassfurt 

 salts, and may contain as high as 97 per cent. K 2 S0 . 

 Low-grade sulphate of potash is about 90 per cent, 

 pure. High-grade sulphate of potash contains about 

 50 per cent, of potassium oxide (K 2 0), and is one of 

 the most concentrated forms of potash fertilizer. It 

 is particularly valuable because it can be safely used on 

 crops as tobacco and potatoes which would be injured 

 in quality if muriate of potash were applied, or if 

 much chlorine were present. 



