58 AGRICULTURE FOR COMMON SCHOOLS 



The supply from this source is now about exhausted. 6. Raw 

 and steamed bone, meat meal, hoof meal, horn meal, wool 

 and hair waste, leather waste, castor pomace, linseed meal, 

 garbage tankage, and many other materials furnish nitrogen 

 from organic sources. 



The chemical nitrogen fertilizers are largely used. 1. Sul- 

 phate of ammonia is a by-product in the manufacture of coke, 

 illuminating gas and bone-black. It contains about 20 per 

 cent, of nitrogen and is quickly available. It should not be 

 used on "sour" land, because it requires the bacteria of the 

 soil to make it available. 2. Nitrate of soda is obtained in 

 Chili, South America. There is a large rainless region there 

 where this mineral is mined by the thousands of tons and 

 shipped to all parts of the world. It is called "Chili salt- 

 petre," and contains about 16 per cent, of nitrogen. The 

 nitrogen in nitrate of soda is quickly available and is easily 

 lost on sandy land by drainage. 3. Nitrate of potash, or 

 common saltpetre, is too costly to be used by farmers for a 

 fertilizer. It contains both nitrogen and potash. 



The phosphoric acid fertilizers are also obtained from two 

 sources, namely, from organic materials and from chemical 

 materials. 1. Ground bone, or raw bone meal, is made from 

 raw bones ground into meal, the finer the better. This con- 

 tains about 4 per cent, of nitrogen and 22 per cent, of phos- 

 phoric acid. They are slowly available and their effect in 

 the ground lasts for several years. Steamed bone differs from 

 ground bone in that it has been thoroughly steamed before it 

 was ground. The steaming takes out the fat and almost all 

 the nitrogen. The per cent, of phosphoric acid is about 28 to 

 30, and the nitrogen about IJ. Steamed bone also becomes 

 useful slowly. 3. There are other forms of bones called ex- 



