ARTIFICIAL AND CONCENTRATED MANURES. 83 



as a manure, is extracted chiefly for the purpose of mak- 

 ing glue and gelatine. 



By boiling or steaming, the bone suffers a loss of its 

 original constituents, the chief result of which is to 

 change the proportions of the nitrogen and phosphoric 

 acid contained in it. Steamed or boiled bone contains 

 more phosphoric acid, and less nitrogen, than raw bone, 

 and is also more variable in composition, the relative 

 percentage of these constituents depending upon the de- 

 gree of steaming or boiling to which the bone has been 

 subjected. 



Bone that has been used for the purpose of making 

 glue, where the chief object is to extract the nitrogenous 

 matter, contains from twenty-eight to thirty per cent of 

 phosphoric acid, and from one and one-quarter to one 

 and three-quarters per cent of nitrogen. The steaming of 

 bone, particularly when conducted at high pressure, also 

 exerts a favorable effect upon the physical and mechani- 

 cal character of the bone. It destroys its original struc- 

 ture, makes it soft and crumbly, and often reduces it to 

 a finer state of division than can be readily accomplished 

 by grinding; and, since it is also free from fat, and is 

 finer, it is more directly useful as a source of phosphoric 

 acid to plants than purer raw bone. 



Experiments have shown that the phosphoric acid in 

 fine steamed bone may all become available in the soil, 

 under average conditions, in one or two seasons; while 

 that in the coarser, fatty raw bone is not completely used 

 in three or four years, and sometimes longer. 



In some cases, the fat is extracted from bone by means 

 of such solvents as petroleum or benzine. These meth- 



