240 SOILS AND MANUEES 



A large part of the bones collected in this country have 

 been cooked, and of those imported from abroad, some 

 have been buried, and others had been exposed to the 

 weather, often for a long time. Ordinary commercial 

 bones have therefore a different composition from the 

 above. They generally contain more ash and less organic 

 matter, and are consequently richer in phosphates and 

 poorer in nitrogen. 



Methods of Treatment. Bones which come into the 

 market in the fresh state are not used directly as 

 manure, but are first subjected to some process for 

 extraction of the fat. The fat is of considerable value 

 as tallow, and after its removal the residue is corre- 

 spondingly richer both in phosphates and nitrogen. The 

 presence of fat in bones makes them much more difficult 

 to grind, and retards their decomposition in the soil. 



Sometimes the fat is extracted with benzine or other 

 suitable solvent, which has little pr no effect on 

 the ossein, but more commonly it is removed by 

 steaming or boiling. After removal of the fat, the bones 

 may be either ground up and sold as manure, or they 

 may be subjected to a further process of steaming in 

 order to extract the gelatine. The residue left after the 

 further steaming crumbles very readily into a fine 

 powder sometimes used as manure under the name of 

 steamed bone flour, or simply steamed bones. It is, of 

 course, comparatively poor in nitrogen. The proportion 

 of nitrogenous matter (ossein) left in the residue de- 

 pends upon the length of time they have been subjected 

 to the steaming or boiling process. When it has been 

 carried very far, the last traces of organic matter are 

 often removed by burning, and bone ash remains. Bone 

 ash has also been used as manure, but there is a Con- 

 siderable demand for it for other purposes, which main- 

 tains the price at a higher level than its agricultural value. 



