Phosphates Their Sources 65 



and is finer, it is more directly useful as a source of phos- 

 phoric acid to plants than purer raw bone. 



In some cases, the fat is extracted from bone by means 

 of such solvents as petroleum or benzine. These methods 

 of extracting the fat have the advantage of increasing 

 the relative proportion of the nitrogen, this element 

 not being attacked by the solvents. The more complete 

 extraction of the fat and moisture by these methods also 

 aids in the final preparation of the bone by grinding. 

 Bone prepared in this way frequently contains as high 

 as 6 per cent of nitrogen and 20 per cent of phosphoric 

 acid. 



The nature and composition of animal bone is such 

 as to make it a valuable source of phosphoric acid ; and, 

 while it is largely used with nitrogenous and potassic 

 materials in the manufacture of artificial manures, its 

 best use is, perhaps, in the fine ground form, particularly 

 for soil improvement and for slow-growing crops. 



Phosphoric acid applied in this form gradually gives 

 up nitrogen and phosphoric acid to the plant; and its 

 physical and chemical characteristics are such that it 

 forms in the soil, during the growing season, no com- 

 pounds more insoluble than the bone itself. 



Commercial grades of bone. 



Because bone and tankage are variable, a guarantee 

 should be required. The market has recognized this as 

 fair, and to-day bone is sold and known more by its guaran- 

 tee rather than by its source. There are a number of 

 grades sold under guarantee of ammonia and bone phos- 

 phate of lime instead of nitrogen and phosphoric acid. 

 The quantities of the different grades are becoming less 

 each year, and there is often some variation in the materials 

 F 



