Aluminium Tungstates

The normal salt, Al₂(WO₄)₃.8H₂O, or Al₂O₃.3WO₃.8H₂O, is obtained as a voluminous white precipitate when solutions of alum and normal sodium tungstate are mixed. It is slightly soluble in water (1 in 1500). Sodium ditungstate with a concentrated solution of alum yields the acid salt, Al₂O₃.4WO₃.9H₂O, soluble in 400 parts of water at 15° C. Another acid salt, Al₂O₃.5WO₃.6H₂O, is formed by the addition of aluminium acetate to sodium tritungstate. It is soluble in water, but is obtained as a white precipitate, which thickens to the consistency of honey, by the addition of alcohol.

Aluminium paratungstate, Al₂O₃.7WO₃.9H₂O, is obtained by precipitating a solution of ammonium paratungstate with an aluminium salt.

By boiling a mixture of aluminium hydroxide and aqueous ammonium paratungstate, a complex salt, ammonium aluminotungstate, 3(NH₄)₂O.Al₂O₃.9WO₃.4H₂O, is obtained as a highly refractive syrup which on drying leaves a semi-transparent mass. Other alumino- tungstates containing the same ratio, Al₂O₃: 9WO₃, have also been prepared, viz.:

8BaO.Al₂O₃.9WO₃.7H₂O;
2CuO.Al₂O₃.9WO₃.161H₂O;
5Hg₂O.Al₂O₃.9WO₃;
1½ZnO.Al₂O₃.9WO₃.8H₂O; and ZnO.Al₂O₃.9WO₃.20H₂O;
11Ag₂O.21(NH₄)₂O.4Al₂O₃.36WO₃.

The following complex tungstates containing aluminium have been described:

Alumino-phosphotungstates,
9(NH₄)₂O.2Al₂O₃.4P₂O₅.9WO₃.13H₂O;
4BaO.2Al₂O₃.4P₂O₅.9WO₃.3H₂O;
4Ag₂O.2Al₂O₃.4P₂O₅.9WO₃.6H₂O;
5ZnO.2Al₂O₃.4P₂O₅.9WO₃.llH₂O.

Alumino-arsenotungstates,
6(NH₄)₂O.2Al₂O₃.3As₂O₅.18WO₃.14H₂O;
4BaO.2Al₂O₃.3As₂O₅.18WO₃.12H₂O;
4CdO.2Al₂O₃.3As₂O₅.18WO₃.17H₂O.

Alumino-antimoniotungstates,
6(NH₄)₂O.2Al₂O₃.3Sb₂O₅.18WO₃.17H₂O;
5BaO.2Al₂O₃.3Sb₂O₅.18WO₃.6H₂O;
6Ag₂O.2Al₂O₃.3Sb₂O₅.18WO₃.12H₂O.