Sodium tungsten bronzes

Sodium tungsten bronzes have been the subject of much investigation and many have been described. The following appear to be well-defined compounds: Na₂W₂O₆. golden-yellow cubic crystals, density 7.28; Na₂W₃O₉, reddish-purple octahedra, density 7.22; Na₂W₄O₁₂, violet needles, density 7.195; Na₂W₅O₁₅, blue cubic crystals; Na₄W₅O₁₅, reddish-yellow crystals; and Na₅W₆O₁₈, yellow cubes.

Engels has described a series of bronzes containing an alkali and an alkaline earth metal. These were prepared by electrolysis of the mass obtained by fusing commercial sodium or potassium tungstate with the calculated amount of metal carbonate.

2BaW₄O₁₂.3Na₂W₅O₁₅, dark blue crystals.
BaW₄O₁₂.5Na₂W₃O₉, yellow-red cubes.
BaW₄O₁₂.5K₂W₄O₁₂, dark red pyramids.
SrW₄O₁₂.5Na₂ W₅O₁₅, brilliant violet pyramids.
SrW₄O₁₂.12Na₂W₃O₉, carmin-red pyramids.
SrW₄O₁₂.5K₂W₄O₁₂, red pyramids.
CaW₄O₁₂.5Na₂W₅O₁₅, violet pyramids.
CaW₄O₁₂.10Na₂W₃O₉, purple cubes or pyramids.
CaW₄O₁₂.5K₂W₄O₁₂, glistening red pyramids.