CHAPTER IV 



PHOSPHA TES THEIR SOURCES, COMPOSI- 

 TION AND RELATIVE VALUE 



MANY farmers apply the term "phosphate" to all 

 manufactured fertilizers, without regard to the kind 

 and character of the fertilizing constituents contained 

 in them. The term "phosphate" should only be ap- 

 plied to materials which contain phosphoric acid, and 

 it does not necessarily imply that the phosphoric acid 

 is in an available form. The term "superphosphate" 

 implies that the phosphoric acid contained in the material 

 is available. The phosphates constitute a class of prod- 

 ucts from which superphosphates are made, and which 

 are used in the manufacture of fertilizers that contain 

 immediately useful or available phosphoric acid. The 

 following discussion of phosphates is quoted from the 

 author's "First Principles of Agriculture." 



The phosphoric acid in artificial manures is derived 

 from compounds called "phosphates." In phosphates 

 the phosphoric acid is united with lime, iron and alumina, 

 forming phosphates of lime, iron and alumina, as the 

 case may be. The phosphates of lime are better cal- 

 culated for the purpose, and are, therefore, used more 

 largely than any other as a source of phosphoric acid, 

 in the manufacture of artificial manures. 



The phosphates available for this purpose are not, 

 however, pure salts, but exist in combination either 



61 



