Cadmium Tungstates

The anhydrous normal salt, CdWO₄, remains as colourless crystals when a mixture containing sodium tungstate (4 parts), sodium chloride (16 parts), and cadmium chloride (11 parts) is heated to complete fusion and allowed to cool. The hydrate, CdWO₄.2H₂O, is formed by double decomposition.

Cadmium paratungstate, 3CdO.7WO₃.16H₂O, is obtained, according to Gonzalez, as a white crystalline precipitate on mixing hot solutions of an alkali paratungstate and a cadmium salt. The crystals are infusible and become orange coloured after heating. Lotz, using ammonium paratungstate, obtained the double salt, 12CdO.3(NH₄)₂O.35WO₃.35H₂O, whilst from solutions containing molecular proportions of sodium paratungstate and cadmium sulphate at 80° C. von Knorre obtained white crystals of composition 2CdO.Na₂O.7WO₃.18H₂O.

The tritungstate, CdO.3WO₃.4H₂O, is obtained as a white translucent gummy mass by mixing solutions of cadmium acetate and sodium tritungstate, and drying at 100° C.