Iridium Trioxide, IrO₃

Iridium Trioxide, IrO₃, has not been isolated in a pure state, and appears to be unstable in the absence of alkali. Oxygen is absorbed when the dioxide is heated with alkali in oxygen, but not in the amount theoretically required to convert the whole into trioxide.

The potassium salt, K₂O.2IrO₃, is described as resulting when potassium nitrate and iridium are fused together.

Another potassium salt, IrO₃.2K₂O.H₂O, is said to be obtained on heating for a couple of hours finely divided iridium with a mixture of potassium hydroxide and nitrate. The black crystalline mass resulting is readily soluble in potash solution, to which it imparts a blue colour.