514 SOILS: PROPERTIES AND MANAGEMENT 



charged with carbon dioxide than in pure water, a property 

 that greatly increases its value because of the fact that 

 soil water always contains more or less of this gas. It is 

 also readily acted upon by organic acids. For this reason 

 it is particularly effective in a peat soil, and likewise in 

 most soils deficient in lime. As it contains a considerable 

 quantity of free lime it has another beneficial effect on 

 such soils. 



432. Superphosphate fertilizers. In order to render 

 more readily available to plants the phosphorus contained 

 in bone and mineral phosphates, the raw material, purified 

 by being washed and finely ground, is treated with sulfuric 

 acid. This results in a replacement of phosphoric acid by 

 sulfuric acid, with the formation of monocalcium phos- 

 phate and calcium sulfate, and a smaller amount of dical- 

 cium phosphate, according to the reactions : 



Ca 3 (PO 4 ) 2 + 2 H 2 SO 4 = CaH 4 (PO 4 ) 2 + 2 CaSO 4 

 Ca 3 (PO 4 ) 2 + H 2 SO 4 = Ca 2 H 2 (PO 4 ) 2 + CaSO 4 



The tricalcium phosphate being in excess of the sul- 

 furic acid used, some of it remains unchanged. 



In the treatment of phosphate rock some of the sul- 

 furic acid is consumed in acting on the impurities present, 

 which usually consist of calcium and magnesium carbo- 

 nates, iron and aluminium phosphates, and calcium chlo- 

 ride or fluoride, converting the bases into sulfates and 

 freeing carbon dioxide, water, hydrochloric acid, and 

 hydrofluoric acid. The resulting superphosphate is there- 

 fore a mixture of monocalcium phosphate, dicalcium phos- 

 phate, tricalcium phosphate, calcium sulfate, and iron and 

 aluminium sulfates. 



In the superphosphates made from bone, the iron and 

 aluminium sulfates do not exist in any considerable 



