PLATINUM METALS AND ORE. 117 



and the metal reduced in a current of hydrogen. The 

 weighed metal is digested with dilute aqua-regia, the 

 solution which contains all the palladium with a little 

 rhodium, evaporated to dry ness, a few drops of caustic 

 potassa added, and the palladium precipitated by a 

 saturated solution of cyanide of mercury. The pre- 

 cipitate is washed, dried, ignited in a stream of hydro- 

 gen, and weighed as metallic palladium. 



The solution which contains the rhodium, is made 

 slightly alkaline with soda, evaporated to dryness, the 

 mass ignited to drive off the mercury and treated with 

 water. The oxide of rhodium which remains undis- 

 solved is added to that left from the solution of the 

 palladium and ignited in hydrogen gas. 



The portion of the salt which contained the platinum 

 and iridium, and which remained insoluble in the 

 chloride of ammonium, is digested with a weak solu- 

 tion of cyanide of potassium added gradually, until the 

 color has changed to a light yellowish-brown, and is 

 converted into a double salt of chloroplatinate of po- 

 tassium and ammonium, which is washed with a so- 

 lution of chloride of ammonium. By dissolving in 

 boiling water it is obtained in dark yellow octahedral 

 crystals. It is ignited, placing in the crucible near 

 the close of the operation some crystals of oxalic acid, 

 and the chloride of potassium extracted with water. 



The filtrate which contains the iridium is evaporated 

 to dryness, ignited to drive off' the chloride of ammo- 

 nium, and finally fused with some nitrate of potassa. 

 The sesquioxide of iridium containing the alkali 

 which remained insoluble when treated with water, 

 is well washed, reduced by hydrogen, and the alkali 

 extracted with water. 



