80 FIRST PRINCIPLES OF AGRICULTURE. 



CHAPTEE VII. 

 Artificial and Concentrated Manures; Phosphates. 



THE phosphoric acid in artificial manures is derived 

 from compounds called "phosphates." In phosphates 

 the phosphoric acid is united with lime, iron, and alu- 

 mina, forming phosphates of lime, iron, and alumina, as 

 the case may be. The phosphates of lime are better 

 calculated 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 with 

 organic substances, or with minerals, or both ; the con- 

 tent of phosphoric acid and its combination with other 

 substances determining the usefulness of the phosphate 

 to the manure-maker. 



The phosphoric acid in these materials is difficultly 

 soluble in the soil water ; and hence in their original con- 

 dition, or in the crude raw forms, they give up this ele- 

 ment in proportion as they decompose or decay in the 

 soil. Those in combination with organic substances, 

 either animal or vegetable, are, as a rule, more quickly 

 useful as a source of phosphoric acid than those com- 

 posed entirely of mineral constituents. 



Animal Bone. The bones of animals are the chief 

 source of phosphates that exist in combination with or- 



