512 SOILS: PROPERTIES AND MANAGEMENT 



steamed. This frees it from fat and nitrogenous matter, 

 both of which are used in other ways. Steamed bone is 

 more valuable as a fertilizer than raw bone, because the 

 fat in the latter retards decomposition and also because 

 steamed bone is in a better mechanical condition. The 

 form of the phosphoric acid is the same as in raw bone 

 and constitutes from 28 to 30 per cent of the product, 

 while the nitrogen is reduced to l| per cent. 



Bone tankage, which has already been spoken of as a 

 nitrogenous fertilizer, contains from 7 to 9 per cent of 

 phosphoric acid, largely in the form of tricalcium phos- 

 phate. All these bone phosphates are slow-acting ma- 

 nures, and should be used in a finely ground form and for 

 the permanent benefit of the soil rather than as an imme- 

 diate source of nitrogen or phosphorus. 



431. Mineral phosphates. — There are many natural 

 deposits of mineral phosphates in different parts of the 

 world, some of the most important of which are in North 

 America. The phosphorus in all these is in the form of 

 tricalcium phosphate, but the materials associated with 

 it vary greatly. 



Apatite is found in large quantities in the provinces of 

 Ontario and Quebec, Canada. It exists chiefly in crys- 

 talline form. The tricalcium phosphate of which it is 

 composed is in one form associated with calcium fluoride 

 and in the other with calcium chloride. The Canadian 

 apatite contains about 40 per cent of phosphoric acid, 

 being richer than that found elsewhere. Phosphorite is 

 another name for apatite, but is chiefly applied to the 

 impure amorphous form. 



Coprolites are concretionary nodules found in the 

 chalk or other deposits in the south of England and in 

 France. They contain from 25 to 30 per cent of phos- 



