2O8 SOILS AND FERTILIZERS 



in a fertilizer retards its action because fat is so slow 

 in decomposing. Bones from which the organic matter 

 has been removed are more active as a fertilizer than raw 

 "bones. There is from 18 to 25 per cent of phosphoric 

 acid and from 2 to 4 per cent of nitrogen in bones. 

 The amount and value of the citrate-soluble phosphoric 

 acid are extremely variable. 



237. Bone Ash is the product obtained when bones 

 are burned. It is not extensively used as a fertilizer 

 because of the greater commercial value of bone black. 

 Bone ash contains about 36 per cent of phosphoric acid, 

 and is more concentrated than raw bones. 



238. Steamed Bone. --Raw bones are subjected to 

 superheated steam to remove the fat and ossein which 

 are used for making soap and glue. They are then pul- 

 verized and sold as fertilizer under the name of bone meal, 

 which contains from 1.5 to 2. 5 per cent of nitrogen and 

 from 22 to 29 per cent of phosphoric acid. Steamed 

 bone makes a more active fertilizer than raw bone. Oc- 

 casionally well-prepared bone meal is used for feeding 

 pigs and fattening stock in the same way that flesh meal 

 is used. The fineness to which the bone meal is ground 

 greatly influences its agricultural value. 



239. Dissolved Bone. When bones are treated with 

 sulphuric acid, as in the manufacture of superphosphates, 

 the product is called dissolved bone. The tricalcium 



