Ferrous met-arsenite, Fe(AsO₂)₂

Ferrous met-arsenite, FeO.As₂O₃ or Fe(AsO₂)₂ has been obtained by the action of potassium hydrogen arsenite, K₂O.As₂O₃.H₂O, upon a dilute solution of ferrous sulphate. It is greenish in colour, becoming brown upon exposure to air. When a hot, saturated solution of arsenious acid containing ferrous iodide is allowed to cool, crystals of the compound FeI₂.4As₂O₃.12H₂O are obtained, which slowly oxidise in air, and in vacuo over concentrated sulphuric yield up all their combined water. The iodide character of the salt is suppressed, from which it may be inferred that the iodine has combined with the arsenious oxide to yield a complex negative radicle.