Iron Tungstates

Ferrous tungstate occurs in the minerals fer- berite and reinite and with manganese in wolframite. It may be prepared in the crystalline form by fusing together sodium tungstate, sodium chloride, and ferrous chloride; the crystals, which are lustrous, black, and opaque, have density 7.1. It is also formed when a mixture of tungstic anhydride and ferrous oxide is strongly heated in a current of hydrogen chloride. The trihydrate, FeWO₄.3H₂O, is precipitated as a light brown powder by the addition of a ferrous salt to sodium tungstate solution.

Ferrous ditungstate, FeO.2WO₃.2H₂O, results as a cinnamon-brown precipitate when a ferrous salt is added to a solution of sodium ditungstate.

Ferric Tungstate. - The cream-coloured precipitate formed on the addition of a ferric salt to a solution of ammonium tungstate is considered by Lotz to be ferric tungstate. The salts, 2Fe₂O₃.3WO₃.6H₂O, Fe₂O₃.2WO₃.4H₂O, and Fe₂O₃.4WO₃.4H₂O, are described by Lefort.

A complex ferritungstic acid and corresponding salts have been isolated, the acid being considered by Rosenheim to be a tetrabasic ferrihexatungstic acid of composition H₉[Fe(WO₄)₆], the ammonium and potassium salts having the formula R^•₄H₅[Fe(WO₄)₆].9H₂O. The latter are precipitated by adding the alkali chloride to a mixture of the alkali paratungstate and ferric chloride. A guanidinium salt, (CH₆N₃)₃H₆[Fe(WO₄)₆].5H₂O, has also been prepared.