GJ)4 RHODIUM. 



and converted into chloride of mercury. The dried mass is 

 reduced to a very fine powder, and washed with alcohol of 

 density 0.837, which takes up the double chlorides of sodium 

 with platinum and iridium, the copper and mercury, but leaves 

 the double chloride of rhodium and sodium in the form of a 

 fine deep red powder. The rhodium is most easily reduced by 

 gently heating the double chloride in a stream of hydrogen gas, 

 and afterwards washing out the chloride of sodium by water. 



Rhodium when rendered coherent, is a white metal like pla- 

 tinum, of which the density is about 11. It is brittle and very 

 hard, and may be reduced to powder. When pure, it is not 

 dissolved by any acid. But when alloyed with certain metals, 

 such as platinum, copper, bismuth or lead, and exposed to 

 aqua regia, it dissolves along with those metals. When fused 

 with gold or silver, however, it is not dissolved with the other 

 metal. But the most eligible mode of rendering rhodium solu- 

 ble, is to mix it in fine powder with chloride of potassium or 

 sodium, and to heat the mixture to low redness in a stream of 

 chlorine gas. A double chloride is then formed, as with the 

 other platinum metals in similar circumstances, which, is very 

 soluble in water. The solutions of rhodium have a beautiful 

 red colour, the circumstance from which the metal derives its 

 name (from poSov, a rose). Rhodium may also be rendered so- 

 luble in the dry way, by fusing it with bisulphate of potash, 

 when the metal is oxidated with the escape of sulphurous acid 

 gas. Rhodium is the most oxidable of the platinum metals, 

 combining with oxygen when heated to redness in an open ves- 

 sel, and very readily when in fine powder and heated to a cherry 

 red heat. It appears to form two oxides, the rhodous and the 

 rhodic, of which, however, the last only has been isolated. 



Oxides of rhodium. Rhodic oxide, R 2 O 3 , is produced when 

 the metal is ignited with hydrate of potash and a little nitre, in 

 a silver crucible. The metal swells up and becomes of a coffee 

 brown, it is then a compound of rhodic oxide and potash, which 

 must be washed with water and afterwards digested in hy- 

 drochloric acid ; the hydrated oxide remains of a grey colour 

 with a shade of green and insoluble in acids. The same hydrated 

 oxide, as obtained from the double chloride of rhodium and 

 potassium or sodium by precipitation with an alkali and evapo- 

 ration, dissolves slowly in acids, with a certain quantity of alkali 

 which is attached to it, assuming a yellow colour and producing 



