Phosphates Their Sources 75 



reaches our markets to-day, but an occasional shipment 

 is brought in from the West Indies or islands of the Pacific 

 Ocean. 



PHOSPHATES AS SOURCES OF PHOSPHORIC ACID TO 

 PLANTS 



The phosphates mentioned constitute what are called 

 " raw materials," and, with the exception of bone, are 

 not largely used directly, or without further treatment 

 to render the phosphoric acid more soluble, and thus 

 more immediately available to plants. As already stated, 

 the phosphoric acid in them becomes food in proportion 

 to the rapidity of decay, which is influenced both by the 

 character of the material and the fineness of its division. 

 Fine materials, too, permit of a more even distribution, 

 thus bringing more particles of phosphate in contact 

 with the roots of plants. 



As already stated, a phosphate is a substance in which 

 the phosphoric acid is combined with lime, iron or alumina. 

 The phosphates of lime are the only ones that are used 

 to any extent in the manufacture of artificial fertilizers. 

 The phosphoric acid contained in animal bone is in the 

 form of phosphate of lime, hence the term "bone phos- 

 phate of lime" has been applied to all phosphates that 

 contain their phosphoric acid as phosphate of lime. In 

 fact, statements of analysis of iron and alumina phos- 

 phates are frequently expressed in terms of phosphate 

 of lime. That is, the content of phosphoric acid is stated 

 as equivalent to a certain percentage of bone phosphate, 

 the term expressing the total amount of combined phos- 

 phoric acid; as, for example, a bone which contains 20 

 per cent of phosphoric acid, which is the average content 



