232 Bureau oe Farmers' Institutes. 



meal with such substances as lime, gypsum, coal-ashes, ground 

 oyster-shells, gTOimd rock-phosphate, etc. 



The composition of bone-meal varies, according to its manner 

 of preparation. Bone-meal from raw bones has the composition 

 given above for raw bones, while bone-meal from steamed bone 

 will contain less nitrogen and more phosphate of lime. 



Steamed Bone. — Raw bones are treated under pressure by 

 steam and by this means the ossein and fat are removed, the 

 ossein being used chiefly for making glue and gelatin and the 

 fat for making soap. The bones after this treatment are very 

 brittle and, when dry, can easily be ground line. The composi- 

 tion of steamed bone depends upon the thoroughness and extent 

 of steaming or boiling. Bone from glue factories averages about 

 1.5 per cent, of nitrogen and 29 per cent, of phosphoric acid. 



In some cases, the fat alone is extracted from bones by some 

 solvent like petroleum or benzine, which removes none of the 

 nitrogen. Such bone may contain as much as 6 per cent, of 

 nitrogen with 20 per cent, of phosphoric acid. 



The thorough steaming of bone appears to change the nature 

 of the nitrogen compounds or perhaps the mechanical condition 

 of the bone in such a way as to permit more rapid decomposition 

 in the soil than in case of raw bone. The presence of easily 

 decaying nitrogen compounds in bone hastens, in the process of 

 decomposition, to render soluble more or less of the insoluble 

 phosphate. 



Bone-Tankage. — While tankage is rich in nitrogen, some 

 grades contain an abundance of phosphoric acid. Several distinct 

 grades of tankage are now recognized, varying in phosphoric acid 

 content from about G to 20 per cent. The higher grades are 

 nearly like bone in their proportion of phosphoric acid. ' The 

 higher the phosphoric acid in tankage, the lower is the nitrogen 

 content. As previously stated, tankage is made from residues 

 obtained from boiling refuse animal matter, heads, feet, etc. 

 Hence the phosphoric acid of tankage may be regarded as having 

 the same agricultural value as the phosphoric acid of steamed 

 bone having the same degree of fineness. 



Bone-Ash. — As the name implies, bone-ash is made simply by 

 burning bones in the open air. The nitrogen is, of course, driven 

 oil' and lost in burning, and the chief constituent is insoluble cal- 

 cium phosphate, equivalent to 30 to 35 or more per cent, of phos- 

 phoric acid. 



