112 PLATINUM METALS AND ORE. 



in alcohol, scarcely soluble in water, a means by 

 which the commercial palladium, iron, and copper may 

 be separated. 



3. IRIDIUM. More fusible than platinum. Specific 

 gravity = 21.15. In its isolated form it is unacted on 

 by any of the acids, or by aqua regia, unless alloyed 

 with platinum. To obtain the metal in the separate 

 state the powdered alloy is intimately mixed with an 

 equal weight of finely powdered chloride of sodium, 

 and the mixture heated to dull redness in a glass tube 

 through which a current of dry chlorine is passed so 

 long as it is absorbed. The resulting dark-red solu- 

 tion of double chlorides gives, with chlorides of am- 

 monium and potassium in a hot solution, a black pre- 

 cipitate of NH 4 Cl + IrCl 2 , or KCl + IrCl 2 . 



If the metal is fused with nitrate of potassa at a 

 strong red heat, or with caustic potassa and chlorate 

 of potassa, it is converted into a black sesquioxide, 

 mixed with potassa. The pulverized metal heated to 

 redness oxidizes in the air. 



4. EHODIUM. More infusible than platinum. After 

 fusion i4 has a specific gravity 12.1. Malleable. If 

 heated to redness in the form of a powder in the air, 

 it oxidizes. Insoluble in aqua regia. It is obtained 

 as a soluble double salt if gently ignited in a stream 

 of chlorine, if pulverized and mixed -with chloride of 

 potassium, or chloride of sodium. Both double salts 

 (2KCl-f K 2 C1 3 ) are easily soluble in water, also the 

 ammonium salt. They are insoluble in alcohol. They 

 form dark-red crystals. t Potassa added to their solu- 

 tions, and then alcohol, a black precipitate of rhodium 

 is formed. The pulverized metal fused for some time 

 with a large excess of bisulphate of potassa, and until 

 the free acid is driven off, forms a mass soluble in 

 water. If chloride of potassium and hydrochloric 

 acid are added to this solution and evaporated, it be- 

 comes rose-red. 



