RHODIUM. 693 



its name (from ovpos odour). Its taste is acrid and burning, 

 but not acid. It becomes soft like wax by the heat of the 

 hand, melts into a colourless liquid like water considerably be- 

 low 212, and enters into ebullition a very little above its point 

 of fusion. It is dissolved slowly, but in considerable quantity, 

 by water. The solution has no acid reaction. Osmic acid is 

 also soluble in alcohol and ether, but these solutions are apt to 

 deposit metallic osmium. It is a weak acid, being incapable of 

 displacing carbonic acid from the carbonates, in the humid way, 

 but forms a class of salts, the osmiates. Osmic acid is expelled 

 by heat from most of its combinations with bases. A terchlo- 

 ride of osmium has been obtained in combination with chloride 

 of ammonium, as a double salt, when osmic acid is saturated 

 with that alkali, and treated, after a time, with an excess of hy- 

 drochloric acid, mercury being also placed in contact with it. 

 After a few days, the liquid loses the odour of osmic acid, and 

 when evaporated to dry ness leaves the double salt, in brown 

 dendritic crystals. The oxide corresponding with this chloride, 

 Os O 3 is hypothetic. It cannot be extracted from the above am- 

 moniacal compound, for when an alkali is added to it, ammo- 

 nia which is set free immediately reduces the precipitated oxide 

 to the state of deutoxide. 



Sulphurets of osmium. Osmium has a great affinity for sul- 

 phur, burning in the vapour of that substance, and appears to 

 have as many degrees of sulphuration, as it possesses oxides. 



SECTION IV. 



RHODIUM. 

 Eg. 651.4 or 52.2; R. 



This metal was discovered, by Wollaston, in the ore of pla- 

 tinum. He found the ore from Brazil to contain 0.4 per cent ; 

 native platinum from another locality has been found with so 

 much as 3 per cent of rhodium. 



After the precipitation of the palladium from the solution of 

 native platinum, by cyanide of mercury, the solution, in order 

 to obtain the rhodium, may be mixed with a little hydrocho- 

 ric acid, and evaporated to dryness. The cyanide of mer- 

 cury in excess is decomposed by the hydrochloric acid, 



