FERTILIZEES AND MANURES. 73 



much less quantity, which, in a state of minute subdi- 

 vision, is dispersed through every part of the soil. A root- 

 let requires, where it touches the soil, a most minute 

 portion of food, but it is necessary for its very existence 

 that this minute supply should be at that precise spot. 

 (Liebig.) 



Dr. L. L. Van Slyke, chemist of the Geneva (New York) 

 Agricultural Station, gives the following excellent ac- 

 count of the origin of phosphoric acid in Bulletin No. 91, 

 New Series, pages 315 to 321: 



"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. Eeverted phosphate of lime. 



1.— INSOLUBLE PHOSPHATE OF LIME. 



"This is known under several other names, as insoluble 

 calcium phosphate, normal calcium phosphate, tri-cal- 

 cium 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 eighty-five per cent, of the ash or inorganic matter 

 of bones. It is also contained in the excrement 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 cannot, therefore, be taken up and used 

 by the plants, except very slowly. To make the insoluble 

 phosphate available for plants so that they can take it up 



