Osmium Hexafluoride, ОsF₆

The proportion of Osmium Hexafluoride, ОsF₆, in the mixture obtained by passage of fluorine over reduced osmium at 250° C. is increased by reducing the rate of passage of the fluorine. The octafluoride, being most volatile, passes farther along from the furnace, being collected in a cooled receiver. The hexafluoride condenses in the tube close by where it leaves the furnace. In order to completely free it from octafluoride it is gently warmed to 50° C. under a pressure of 20 mm., when it sublimes and condenses on a cool part of the tube as a light green crystalline deposit. It has not been obtained in a perfectly pure condition as it proved to be extremely difficult to obtain entirely free from oxide. Its boiling-point is approximately 202° to 205° C., whilst its melting-point lies between 50° and 120° C. The latter constant could not be obtained accurately as the fluoride becomes black upon heating in contact with glass. Osmium hexafluoride is decomposed by water, yielding hydrofluoric acid and oxides of osmium. In caustic soda it gives a reddish yellow colour similar to that of the hexachlorosmates.