Nickel Tungstates

The anhydrous normal salt is obtained in well-defined, brown, lustrous, translucent, rhombic prisms, of density 6.88, by fusing together sodium tungstate, sodium chloride, and nickel chloride. The hydrates, NiWO₄.3H₂O and NiWO₄.6H₂O, are obtained by precipitation as light green powders which yield the anhydrous salt on heating.

The acid tungstates, NiO.2WO₃.5H₂O, NiO.2WO₃.7H₂O, and NiO.3WO₃.4H₂O, are described by Lefort.

Nickel paratungstate, 3NiO.7WO₃.14H₂O, is obtained as a light green precipitate when solutions of a nickel salt and an acid tungstate of sodium are mixed.

The salt, 4NiO.10WO₃.34H₂O, obtained in a similar manner to the barium salt, is a greenish-white powder.

By the addition of a nickel salt to a large excess of alkali paratungstate, Rosenheim has prepared well-defined crystalline salts, corresponding to the ferri-tungstates, for which he suggests the formulae: Na₃H₇[Ni(WO₄)₆].18H₂O, or Na₃NiH₅[H₂(WO₄)₆].18H₂O, and (NH₄)₃H₇[Ni(WO₄)₆].7.5H₂O, or (NH₄)₃NiH₅[H₂(WO₄)₆].7.5H₂O.

Complex salts containing trivalent nickel, and of composition 3(NH₄)₂O.Ni₂O₃.16WO₃.22H₂O and 2(NH₄)₂O.Ni₂O₃.8WO₃.14H₂O, are obtained by boiling hydrated nickel dioxide with an ammoniacal ammonium paratungstate solution.