“ Several oxides of osmium are known. The protoxide, OsO, is obtained as a dark grey insoluble powder when osmium sulphite is heated with sodium carbonate in a current of carbon dioxide. The sesquioxide, Os2O3, results on heating osmium with an excess of the tetroxide. The dioxide, OsO2, is formed when potassium osmichloride is heated with sodium carbonate in a current of carbon dioxide, or by electrolysis of a solution of the tetroxide in the presence of alkali. ”

“ Potassium osmiate, K2OsO42H2O, formed when an alkaline solution of the tetroxide is decomposed by alcohol, or by potassium nitrite, crystallizes in red octahedral. It is stable in dry air, but in moist air rapidly decomposes. The tetroxide, OsO4, is formed when osmium compounds are heated in air, or with aqua regia, or fused with caustic alkali and nitre. ”

“ The osmiates, corresponding to the unknown trioxide OsO3, are red or green coloured salts; the solutions are only stable in the presence of excess of caustic alkali; on boiling an aqueous solution of the potassium salt it decomposes readily, forming a black precipitate of osmic acid, H2OsO4. ”