240 



SOILS AND FERTILIZERS 



form of monocalcium phosphate. The citrate-soluble 

 is mainly dicalcium phosphate with variable amounts 

 of iron and aluminum phosphates in easily soluble 

 forms. The insoluble phosphoric acid is tricalcium 

 and other phosphates, as iron and aluminum, which 

 are soluble only in strong mineral acids. The insoluble 

 phosphoric acid in fertilizers is considered as having 

 but little value. As in the case of nitrogen, three 

 fertilizers may have the same total amount of phos- 

 phoric acid and yet have entirely different values. 



No. 3 has little value ; it contains insoluble phos- 

 phate rock or some material of the same nature. No. i 

 is the most valuable, because it contains dissolved 

 phosphate rock or dissolved bone and but little insoluble 

 phosphoric acid. No. 2 is composed of such materials 

 as the best grade of basic slag or roasted aluminum 

 phosphate or fine steamed bone. 



288. Potash. The three forms of potash in fertili- 

 zers are: (i) water-soluble, (2) acid-soluble, and (3) in- 

 soluble. Sulphate of potash, kainit, and muriate of 



