OSMIUM. (>91 



Carburet of indium. When a coherent mass of iridium is 

 held in the flame of a spirit lamp, black masses appear on its 

 surface,, which are a carburet, containing 19.83 per cent of car- 

 bon, or Ir C 4 . The carbon burns off readily in the air. 



OSMIUM. 

 Eq. 1244.5 or 99.72; Os. 



In the treatment of the alloy of iridium and osmium, the lat- 

 ter is separated as a volatile oxide, or osmic acid. To obtain 

 the metal, a solution of osmic acid is mixed with hydrochloric 

 acid, and digested with mercury in a well closed bottle at a 

 temperature of 104 (40 cent.). The osmium is reduced by the 

 mercury, and an amalgam formed, which is distilled in a retort 

 till all the mercury and calomel formed are removed : osmium 

 remains as a black powder without metallic lustre. When ren- 

 dered coherent, osmium is a white metal, less brilliant than pla- 

 tinum, and very easily pulverised. Its density is about 10. 

 As obtained from the amalgam, osmium is highly combustible ; 

 when a mass of it is ignited at a point, it continues to redden, 

 and burns without residue, being converted into the volatile 

 oxide or osmic acid. Osmium in the same condition is oxi- 

 dated by nitric acid or aqua regia, and the osmic acid formed 

 distils over with the water and acid. But after being exposed 

 to a red heat, osmium becomes much less combustible in air, 

 and is not oxidated by the humid way, resembling silicon and 

 titanium in that respect. Five different oxides of this metal are 

 enumerated, but osmic acid is the only one of these which is 

 formed directly; the others are obtained by the decomposition 

 of corresponding chlorides. The three lowest of these oxides 

 are analogous in composition to the oxides of iridium. 



Chlorides and oxides of osmium. When osmium is heated in a 

 long glass tube by a spirit lamp and chlorine gas passed over it, 

 two chlorides are formed, which condense separately in the tube, 

 owing to a difference in their volatility. The protochloride, 

 OsCl, which is the least volatile, crystallizes in needles of a 

 deep green colour. It is deliquescent, and forms a green solu- 

 tion remarkable for its beauty. This solution is instantly dis- 

 coloured by great dilution, metallic osmium is deposited, and 

 hydrochloric and osmic acids remain in solution. Chloride of 



