Chemical elements
    Physical Properties
    Chemical Properties
    Slow Oxidation
    Phosphatic Fertilisers
      Sources of Phosphates
      Composition of Phosphorites
      Distribution of Phosphatic Rocks
      Oceanic Deposits and Guanos
      System Lime
      Changes during Neutralisation
      Acid Phosphates
      Manufacture of Superphosphate
      Potassium Phosphates
      Ammonium Phosphates

Potassium Phosphates

Basic or neutral phosphates (Rhenania phosphates) may be made directly from rock phosphate by mixing it with potassium chloride, some form of carbon and soda, and heating to over 1000° C. in an electric furnace. One of these products has the composition Ca2KNaP2O8, with some silica. Such products may contain 23 to 31 per cent, of soluble phosphoric acid. Potassium superphosphate has been made by mixing potassium sulphate and calcium carbonate with concentrated phosphoric acid in a lead-lined vessel. The CaSO4.2H2O is separated and the filter-pressed solution is evaporated to dryness by steam heat. The residue may be treated with more phosphoric acid and again evaporated. The reaction is expressed by the equation

K2SO4 + 2H3PO4 + CaCO3 = 2KH2PO4 + CaSO4 + CO2 + H2O

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