Ferrous pyrosulphate, FeS₂O₇

Ferrous disulphate or Ferrous pyrosulphate, FeS₂O₇, is precipitated as a white powder by mixing a saturated solution of ferrous sulphate with several times its volume of concentrated sulphuric acid. Examined under the microscope, it is seen to consist of fine prismatic crystals, which absorb water on exposure to air.