ENRICHING SOIL COMMEBCIAL RESOURCES 95 



Water ~\ H 2 O ~\ 



Lime v Phosphoric acid ; or, CaO v PjOs 

 Lime j CaO ) 



This is di- (or two) calcic phosphate. This is 

 insoluble in rain-water, but becomes soluble in 

 the soil-water. 



145. If two parts of the lime be united with 

 sulfuric acid and their places be taken by water, 

 there remains : 



Water ~\ H 2 O ~| 



Water V Phosphoric acid ; or, H 2 O V p 2 O 5 

 Lime ) CaO ) 



This is mono- (or one) calcic phosphate. This 

 is readily soluble in soil water, but in the soil it 

 tends to become insoluble, or to revert to the 

 dicalcic form (and is then said to be "reverted"), 

 and some of it may eventually become tricalcic 

 and unavailable. The lime that is removed by 

 the sulfuric acid unites with the sulfuric acid to 

 form calcium sulfate ; that is, plaster or gypsum 

 (CaSOO- The dicalcic and monocalcic are the 

 forms that are known as acid phosphate, and 

 sold in commercial fertilizers. 



4. Potash (potassium oxide, K 2 O) 



146. Next to phosphoric acid, potash is the 

 most important mineral plant -food. It is placed 

 after phosphoric acid in importance not be- 



