Potassium Iridi-nitrite, K₃Ir(NO₂)₆

Potassium Iridi-nitrite, K₃Ir(NO₂)₆, which is conveniently prepared by adding sodium nitrite to a hot acidulated solution of sodium chlor-iridite until it is bleached. The solution is boiled to expel nitrous oxides, and potassium chloride is added in excess, whereupon iridium potassium nitrite is precipitated as a white mass.

It is also formed by adding potassium nitrite to a solution of iridium sulphate in the warm. It is a white powder, which readily dissolves in boiling water, but which is insoluble in potassium chloride solution.

At 300° C. it begins to decompose, whilst at 440° C. decomposition is rapid. Heated in vacuo at this latter temperature, nitrogen and nitric oxide are liberated, a greenish black powder remaining behind. This, on treatment with water, leaves after a time a heavy black powder consisting of 6IrO₂.K₂O, which, it is suggested is probably the salt of the hypothetical hexiridous acid, (IrO)₆O₅(OH)₂ or 6IrO(OH)₂ - 5H₂O. When the double nitrite is heated to redness in a muffle, the residue on thorough washing has the composition 12IrO₂.K₂O, which Joly and Leidie suggest may be the potassium salt of the hypothetical dodeca-iridous acid, (IrO)₂O₁₁(OH)₂ or 12IrO(OH)₂ - 11H₂O. It is very doubtful, however, if we are justified in assuming that these are separate chemical entities.