ARTIFICIAL AND CONCENTRATED MANURES. 85 



sisting chiefly of carbon and phosphate of lime, though 

 also containing small amounts of magnesia and carbonate 

 of lime. 



Bone-black, as received from the refineries, contains the 

 impurities gathered there, consisting chiefly of vegetable 

 matter and moisture. It is somewhat variable in compo- 

 sition, containing from thirty-two to thirty-six per cent 

 of phosphoric acid and a small amount of nitrogen. It 

 decays slowly in the soil, and is not now used to any 

 extent directly as a manure. 



Bone-ash. Bone-ash, though not a large, is an ex- 

 cellent source of phosphoric acid. It is exported in con- 

 siderable quantities from South America, where the bones 

 are burned, and the bulk reduced, in order to facilitate 

 transportation. It does] not contain nitrogen, and is more 

 variable in composition than bone-black, though usually 

 somewhat richer in phosphate of lime. Good samples 

 contain from twenty-seven per cent to thirty-six per cent 

 of phosphoric acid. 



Bones themselves, and the phosphates derived from 

 bones, constitute a class differing from other phosphates 

 used in making manures, in that they are derived directly 

 from organic materials ; and, as a class, they possess char- 

 acteristics due to this fact, which render them more use- 

 ful than those derived from purely mineral sources. 



Mineral Phosphates. These constitute a class of 

 products differing from those of immediate or recent ani- 

 mal origin, mainly in the fact that they are not combined 

 with organic matter, and are more dense and compact in 

 their structure. They occur in several different forms, 

 and are procured from distinct sources. 



