SEVENTEENTH CHAPTER. 



OUR SOURCES OF PHOSPHORIC ACID. 



TTHE CHIEF sources of phosphoric are four in 

 number; namely: (1) bones of animals; (2) 

 phosphate rocks, which are the fossil remains of 

 pre-historic marine animals; (3) phosphatic guanos; 

 (4) the mineral apatite. Of these, fresh animal 

 bones rank first in people's esteem, although there 

 can be no doubt that phosphoric acid in a soluble 

 condition has exactly the same value whether de- 

 rived from fresh bones or any other source. Some- 

 times the agricultural chemist concedes to the fresh 

 bone phosphate more than is just; and practical re- 

 sults must always be the first criterion. 



The bones used for the manufacture of fertilizers 

 come chiefly from slaughter-houses and butcher- 

 shops, or are picked up here and there. Fresh bone 

 has nearly one-half of its weight of organic 

 matter — that is, gelatine, water, etc. — and 

 one-half of its weight phosphate of lime. Nearly 

 one-half of the. weight of the latter is the phos- 



