118 CONSERVATION AND IMPROVEMENT OF SOIL 



the greatest difficulties in the use of this material is its tendency 

 to lose ammonia, because of this change in composition. It is 

 sometimes mixed with a little dry peat to help hold the ammonia. 

 It does not tend to make soils acid, but acts in the very opposite 

 way because of the great amount of lime present. 



Our greatest interest in the production of calcium cyanamid lies 

 in the fact that its production is unlimited. The products from 

 which it is made, atmospheric nitrogen, carbon and lime, are inex- 

 haustible. The danger that other sources of nitrogen for fertilizing 

 purposes will soon become exhausted, or nearly so, has been the 

 great fear of all mankind. But man can always make use of legumi- 

 nous crops in farm rotations and thus acquire nitrogen from the air. 



Phosphoric Acid. There are two main sources of phosphoric 

 acid: (1) animal substances; (2) phosphate rock. 



Animal bone is the chief source of phosphoric acid. It was much 

 used as a fertilizer before rock phosphate was known to be avail- 

 able for this purpose. Indeed bone phosphate is considered so 

 valuable that much of the rock phosphate is sold as bone. This is 

 due to a false belief that the bone is better than the rock form. A 

 good sample of raw bone meal contains about four per cent of 

 nitrogen and twenty to twenty-five per cent of phosphoric acid, 

 but samples poorer in both of these ingredients are often used. 

 To make the phosphoric acid in bone more readily available it is 

 put through a steaming process. "Steam bone" is sold on the 

 market, containing as much as twenty-five or thirty per cent of 

 phosphoric acid. During the process of boiling or steaming the 

 nitrogen content is usually reduced to almost nothing. But the 

 phosphoric acid is made more available. 



Rock phosphate is obtained from a number of deposits in 

 South Carolina, Florida, Tennessee, Utah, Wyoming, and Idaho. 

 The rock as quarried from the earth is used in two ways: (1) In 

 a form called "floats." In this condition the natural rock is 

 ground very fine and applied to soils, yielding phosphoric acid 

 very slowly to plants. It may be applied only once in three or 

 four years, but the applications are very heavy; perhaps a thou- 

 sand pounds or more per acre at a time. (2) The rock may be 

 ground and afterward treated with strong sulfuric acid to change 

 the composition from calcium phosphate to acid phosphate. The 

 sulfuric acid takes from the natural rock a part or all of its calcium, 

 forming calcium sulfate or land plaster, which remains mixed with 

 the phosphoric acid. The resulting mixture is sold under the 



