90 FIRST PRINCIPLES OF AGRICULTURE. 



CHAPTER Vin. 



Artificial and Concentrated Manures ; Superphosphates and Potash 



Salts. 



PHOSPHATE of lime is a chemical salt capable of exist- 

 ing in three forms. The first consists of three parts of 

 lime and one part of phosphoric acid; this is the insolu- 

 ble form, and it exists as such in all natural phosphates. 

 This form, because of the three parts of lime contained 

 in it, is also called "tricalcic," "tribasic," or "three- 

 lime phosphate." The second form consists of two parts 

 of lime and one of phosphoric acid, and is called " dical- 

 cie," " dibasic," or " two-lime phosphate ; " it is insoluble 

 in water, but readily soluble to the roots of plants. The 

 third form consists of one part of lime and one of phos- 

 phoric acid, and is called " monocalcic," "monobasic," 

 "acid phosphate," or "superphosphate." This form is 

 completely soluble in water, readily distributes itself 

 everywhere in the soil, and is immediately available to 

 plants. A " tetrabasic," or "four-lime phosphate," has 

 been found in basic slag. This form, though insoluble 

 in water, breaks up readily and is more available than 

 the insoluble "tribasic" form. 



Superphosphates, or soluble phosphates, are made from 

 the raw materials containing insoluble tricalcic phos- 

 phate, by first grinding them to a powder and then 



