Phosphates Their Sources 67 



phoric acid; the nitrogen increases as the phosphoric 

 acid decreases, as already pointed out in the discussion 

 of nitrogenous materials. 



Other organic products. 



There are also other products which should not be 

 disregarded in a discussion of phosphates, though because 

 of their content of either nitrogen or potash they are 

 primarily valued for them, rather than for the phos- 

 phoric acid. A good example is the dried ground fish, 

 which often contains as high as 8 per cent of phosphoric 

 acid, or an equivalent of 17 to 18 per cent of bone phos- 

 phate of lime. The phosphoric acid in dried fish is fre- 

 quently more available than in other organic forms, 

 owing to the fact that in the drying of the scrap it is 

 often necessary to add sulfuric acid to prevent putre- 

 faction. On the average, more than one-half of the 

 total phosphoric acid in this product is in an available 

 form. 



The phosphoric acid contained in other nitrogenous 

 products, as cotton-seed meal and castor pomace, while 

 not large, is of some importance, as it is relatively more 

 available than in raw bone or in tankage. 



Bone-black, or animal charcoal. 



This material becomes an important source of phos- 

 phoric acid for artificial manures, after it has served its 

 chief and first purpose in clarifying sugar. In making 

 bone-black, only the best bones are used ; they are cleaned 

 and dried, and placed in air-tight vessels, and heated 

 until all volatile matter is driven off ; the resultant prod- 

 uct, which retains in part the original form of the bone, 

 is then ground to a coarse powder; it then becomes a 



