New York Agricultural Experiment Station. 65 



(b) Fertilizing Materials Containing Phosjphoric Acid Compounds. 



Phosphoric acid is generally found in combination with lime 

 (calcium), forming;, at least, three different compounds, viz. : 



(1) Insoluble phosphate of lime. 



(2) Soluble phosphate of lime. 



(3) Reverted phosphate of lime. 



(1) Insoluble Phosphate of Lime. 



This is known under several other names, as "insoluble calcium 

 phosphate," " normal calcium phosphate," " tri-calcium phosphate," 

 " bone phosphate of lime," etc. 



This form of calcium phosphate is called insoluble because it 

 does not dissolve in water. 



It is found in nature in large quantities in several minerals, which 

 will be noticed later. It also constitutes about 85 per cent, of the 

 ash or inorganic matter of bones. It is also contained in the excre- 

 ment of animals, as in guano, etc. 



Insoluble phosphate of lime is found everywhere in the soil. 

 However, in this form, calcium phosphate has the least value for the 

 farmer, because it is not easily dissolved and can not, therefore, be 

 taken up and used by plants, except very slowly. To make the 

 insoluble phosphate available for plants so that they can take it up, 

 the insoluble phosphate must be converted into some form which is 

 soluble, that is, which dissolves in water. This can be done by 

 treating it with sulphuric acid (oil of vitriol). 



(2) Soluble Phosphate of Lime. 



This is known under several other names as "acid phosphate of 

 lime," "acid calcium phosphate," " acid phosphate," " superphosphate 

 of lime," " superphosphate," " mono calcium phosphate," etc. It 

 is not found naturally occurring. 



As indicated above, the soluble calcium phosphate is made by 

 treating insoluble calcium phosphate with sulphuric acid. By this 

 treatment, a portion of the calcium is removed from the phosphate 

 and unites with the sulphuric acid, forming calcium sulphate or 

 sulphate of lime, in addition to the soluble phosphate. This mix- 

 ture of the soluble phosphate and sulphate of calcium is known as 

 "superphosphate of lime." The phosphate in this form, being 

 easily soluble in water, can be readily taken up by plants and is, 

 5 



