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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;
ZnO.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.

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