The residue so obtained is then powdered and ignited with barium nitrate, which converts the iridium into its oxide and the osmium into barium osmiate.
On fusion with caustic potash it yields potassium osmiate.
Potassium osmiate, K 2 0sO 4 2H 2 0, formed when an alkaline solution of the tetroxide is decomposed by alcohol, or by potassium nitrite, crystallizes in red octahedra.