COMMERCIAL FERTILIZERS 



from which the oil has been pressed. It is a most 

 valuable source of nitrogen for the South. 



The nitrogen in the dried blood, tankage, fish 

 scrap and cotton-seed meal, being organic nitrogen, 

 must be changed by the process of nitrification to 

 nitric acid or nitrate before it is available. They 

 are therefore better materials to use for a more 

 gradual and continuous feeding of crops than the 

 nitrate of soda or sulphate of ammonia. 



Scrap leather, wool waste, horn and hoof shav- 

 ings are rich in nitrogen but they decay so slowly 

 that they make poor fertilizers. They are used by 

 fertilizer manufacturers in making cheap mixed fer- 

 tilizers. 



SOURCES OF PHOSPHORIC ACID 



The principal commercial sources of phosphoric 

 acid are : 



Phosphate Rocks. 



Bones. 



Fish scrap. 



Phosphate slag. 



The Phosphate Rocks are found in shallow mines 

 in North and South Carolina, Georgia, Florida and 

 Tennessee, and also as pebbles in the river beds. 

 They are the fossil remains of animals. After be- 

 ing dug from the mines the rock is kiln dried and 

 then ground to a very fine powder called " floats " 

 which is used on the soil. The phosphoric acid in 

 the floats is insoluble and becomes available only as 

 the phosphate decays. This is too slow for most 



