THE USE OF MANURES. 



57 



the offal of slaughter-houses, are among the most 

 stimulating substances used to promote the growth 

 of vegetation. The animal structure contains every 

 element of the plant except silicon, and some por- 

 tions of the body contain most valuable constituents 

 in a highly concentrated form. The products of 

 decomposition are especially rich in nitrogen. 



127. The bones and excrements of animals, 

 among the most powerful and valuable of fertilizers, 

 generally undergo some manipulation, or preparation 

 before being used, which renders them more suit- 

 able for immediate use, or more convenient for 

 handling. 



128. Raw bones when dried consist chiefly of 

 tricalcium phosphate (common phosphate of lime) 

 and gelatinous matter, in the proportion of about 

 two-thirds of the former to one-third of the latter. 

 Their average composition may be stated as follows : 



Per cent. 



Animal matter 33 



Tricalcium phosphate , 57 



Calcium carbonate 8 



Calcium fluoride I 



Magnesium phosphate I 



129. Bones are sometimes merely ground to a 

 fine powder, and sown broadcast, or drilled with the 

 grain at the time of planting. In this case their ac- 

 tion is slow, because they are insoluble in water, and 



