Barium Tungstate, BaWO₄

Barium Tungstate, BaWO₄, is obtained as a heavy white precipitate from hot solutions of sodium tungstate and barium chloride. This method has been suggested for the estimation of tungsten. The salt can also be prepared by fusing sodium tungstate with barium and sodium chlorides, when it forms quadratic octahedra of density 6.35 at 20° C. The precipitated salt is hydrated, the amount of water present depending on the method of preparation. A gelatinous compound with 4 molecules of water has been obtained, and a crystalline one with 2 molecules, and still other variations have been mentioned.

Barium tungstate is more soluble in ammonium nitrate solutions than in pure water, and is decomposed by acids with the separation of yellow tungstic acid. Its employment in painting has been suggested.

Numerous acid tungstates have been described, including paratungstates and metatungstates.

A number of complex compounds, thio-, phospho-, arseno-, boro-, silico-, and vanadio-tungstates are known, and also a number of double salts with the alkalies and ammonia.

A barium tungsten bronze, BaO.WO₂.4WO₃, has been prepared by reducing barium paratungstate with hydrogen at red heat, and there are also barium alkali compounds similar to the calcium and strontium alkali bronzes.