Potassium Tungsten Bronze, K₂W₄O₁₂

Potassium Tungsten Bronze, K₂W₄O₁₂, is obtained by fusing together potassium carbonate and tungstic acid and reducing the mass by coal gas, hydrogen, or tin; or by electrolysis of the fused paraungstate. It yields reddish-violet prisms of density 7.1; a suspension appears blue by transmitted light and green by reflected light. According to von Knorre and Schaefer this is the only potassium bronze which exists; other bronzes, for example K₂W₃O₉ and K₂W₅O₁₅, have, however, been described.

Two potassium sodium tungsten bronzes have been prepared, 5K₂W₄O₁₂.2Na₄W₅O₁₅ and 3K₂W₄O₁₂.2Na₂W₃O₉. Both are dark red; the former has density 7.117 and when powdered becomes blue.