70 COTTON CULTURE 



three of these forms of plant food. The tables given at 

 the end of this chapter show the composition of the most 

 commonly used fertilizers. 



MATERIALS SUPPLYING POTASH 



Kainit is the most common product of the German 

 potash mines. It is a mixture of several different com- 

 pounds, containing twelve to thirteen per cent of actual 

 potash, together with about thirty-five per cent of common 

 salt, also magnesia salts. 



Muriate of Potash, also a product of the Stassfurt 

 mines, is the main source of supply for potash for commer- 

 cial fertilizers in our market, and contains from fifty to 

 fifty-three per cent of actual potash. 



Sulfate of Potash is a product of the German mines 

 and as found in the market contains from forty-eight to 

 fifty-one per cent of actual potash. 



Sulfate of Potash Magnesia is known also as double 

 manure salt, or low-grade sulfate of potash. This ma- 

 terial contains twenty-six to twenty-eight per cent of 

 actual potash and thirty-two to thirty-six per cent of 

 sulfate of magnesia. 



Wood Ashes contain a small amount of potash, which is 

 present chiefly in the form of carbonate. 



MATERIALS SUPPLYING PHOSPHORIC ACID 



Bones consist chiefly of phosphate of lime, which con- 

 stitutes from one-half to three-fifths of the weight of the 

 bone. The remaining portion is a soft, flesh-like sub- 



