80 The Sugar-Beet in America 



steamed or burned to remove fat and nitrogenous ma- 

 terials which are used for other piu-poses. The fine 

 grinding of bone makes its phosphorus more readily avail- 

 able. Tankage relatively high in bone is used largely for 

 its phosphorus; if high in flesh scraps it is valuable for 

 its nitrogen. Bone is sometimes treated with sulfuric 

 acid to render its phosphorus more available. 



Mineral phosphorus is found in several kinds of rock, 

 which usually have the phosphoric acid in combination 

 with lime, iron, and aluminum. The presence of the 

 last two elements reduces the availability of the phos- 

 phorus. Rock phosphates are used in various ways. 

 Formerly practically all of the rock was treated with 

 sulfuric acid to form super-phosphate, or acid phosphate 

 as it is often called ; but of late years the use of finely 

 ground raw rock-phosphate has increased, especially in 

 soils rich in organic matter. The acid phosphate is doubt- 

 less more immediately available than the raw rock, but 

 it is also much more expensive. 



In the manufacture of steel from pig-iron, much phos- 

 phorus is removed with the basic slag, called Thomas 

 slag. It is often ground and used as a fertilizer. 



Potassiiim. 



Most of the potash fertilizers used in the world have in 

 the past come from the Stassfurt deposits in Germany. 

 Here many minerals rich in potash are found. Some of 

 these are ground and put directly on the land ; others are 

 leached with water to concentrate them before being 

 used. Kainit and silvinit are among the most common 

 of these minerals. 



