PHOSPHATE FERTILIZERS 335 



organic matter, in which case they generally carry some 

 nitrogen. Phosphates associated with organic matter 

 decompose more quickly in the soil than untreated 

 mineral phosphates. 



199. Bone phosphate. Formerly, bones were used 

 entirely in the raw condition, ground or unground. 

 When ground, they are a more quickly acting fertilizer 

 than when unground. Raw bones contain about 22 

 per cent phosphoric acid and 4 per cent nitrogen. The 

 phosphorus is in the form of tricalcic phosphate (Ca 3 

 (P0 4 ) 2 ). 



Most of the bone now on the market is first boiled or 

 steamed, which frees it from fat and nitrogenous matter, 

 both of which are used in other ways. Steamed bone 

 is a more valuable fertilizer than raw bone, as 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 28 to 30 per cent of the product, while 

 the nitrogen is reduced to H per cent. 



Bone tankage, which has already been spoken of as a 

 nitrogenous fertilizer, contains from 7 to 9 per cent 

 phosphoric acid, largely in the form of tricalcium phos- 

 phate. All of these bone phosphates are slow-acting 

 manures, and should be used in a finely ground form, 

 and for the permanent benefit of the soil rather than as 

 an immediate source of nitrogen or phosphorus. 



200. Mineral phosphates. There are many natural 

 deposits wof mineral phosphates in different portions of 

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

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



