Manganese Tungstates

The anhydrous normal salt, MnWO₄, occurs in the mineral hubnerite and with ferrous tungstate in wolframite. It may be prepared by the method used for the normal magnesium salt, and yields light brown, highly lustrous, rhombic crystals, transparent and of density 6.7. The dihydrate, MnWO₄.2H₂O, is precipitated from solutions of manganous salts by the addition of sodium tungstate as a greyish-white powder which becomes anhydrous on heating.

Manganese paratungstate, 3MnO.7WO₃.20H₂O or 5MnO.12WO₃.

34H₂O, is formed as an amorphous white precipitate on adding a solution of a manganous salt to sodium paratungstate. The salt is soluble in dilute hydrochloric acid. It becomes yellowish green after ignition. By mixing solutions of sodium paratungstate and manganese sulphate in molecular proportions at 70° C. the pale yellow crystalline double salt, 3Na₂O.3MnO.14WO₃.36H₂O, is obtained, whilst with potassium paratungstate the double salt, 3K₂O.2MnO.12WO₃.16H₂O, results as small yellow prismatic crystals which are slightly soluble in water and lose 10H₂O on heating at 100° C. By boiling ammonium paratungstate and manganic hydroxide with water, large red octahedral crystals, of composition 4(NH₄)₂O.Mn₂O₃.12WO₃.23H₂O, are obtained4 on evaporation.

The salt, 4MnO.10WO₃.30H₂O, is prepared by the method described for the corresponding barium salt. It is a colourless granular powder.

Manganese tritungstate, MnO.3WO₃.5H₂O, is obtained by double decomposition in presence of alcohol.

A complex tungstate, of composition 3Na₂O.5WO₃.MnO₂.18H₂O or Na₆H₂[MnO(WO₄)₅].17H₂O, has been prepared by the action of excess of sodium tungstate on manganese sulphate in presence of ammonium persulphate; reddish-brown crystals separate which are easily decomposed by water.