182 SOILS AND FERTILIZERS 



slow in decomposing and slow in their action as a fer- 

 tilizer. Before being used as fertilizer they should be fer- 

 mented in a compost heap with wood ashes in the fol- 

 lowing way : A protected place is selected so that no 

 losses from drainage will occur. A layer of well-com- 

 pacted manure is covered with wood ashes, the bones 

 are then added and well covered with manure and 

 wood ashes. From three to six months should be al- 

 lowed for the bones to ferment. The large, coarse 

 pieces may then be crushed and are ready for nse. 

 The presence of fatty material 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. Bones 

 contain from 18 to 25 per cent, of phosphoric acid and 

 from 2 to 4 per cent, of nitrogen. The amount and 

 value of the citrate-soluble phosphoric acid in bones 

 are extremely variable. 



222. 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. 

 It contains about 36 per cent, of phosphoric acid, and 

 is more concentrated than raw bones. 



223. Steamed Bones. — Raw bones are subjected to 

 superheated steam to remove the fat and ossean 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 nitro- 



