for procuring pure Platinum. 259 



colour ; while others, fewer in number, are square prisms of a 

 yellowish-green colour. These last are ammonio-muriate of 

 palladium." Thus we see that the ammonio-muriate of palla- 

 dium has remained in solution, contrary to the statement above. 

 Dr. WoUaston's original method of separating rhodium from 

 palladium and platinum is peculiarly elegant and economical, 

 while it is perfectly exact. Into the solution deprived of the 

 greater part of its platinum by sal-ammoniac, he immerses a 

 piece of clean zinc. This throws down all the metals in the state 

 of a black powder, except the iron, which remains in the solu- 

 tion. The copper and lead of the precipitate, weighing from 

 40 to 50 grains, being removed by very dilute nitric-acid, the 

 remainder after being washed, was digested in dilute nitro-muri- 

 atic acid, which dissolved the greater part. " To this solution 

 were added 20 grains of common salt, equal to one-fifth of the 

 ore employed : and when the whole had been evaporated to dry- 

 ness with a very gentle heat, the residuum, which I had found 

 from prior experiments would consist of the soda-muriates of 

 platina, palladium, and of rhodium, was washed repeatedly with 

 small quantities of alcohol, till it came off nearly colourless. 

 There remained a triple salt of rhodium, which by these means 

 is freed from all impurities*." From the solution of this soda- 

 muriate in water, zinc throws down the metal in a black powder, 

 which may be agglutinated into a somewhat spongy metallic 

 mass, by the heat of a very powerful furnace. Dr. Clarke, of 

 Cambridge, is the only chemist, I believe, who has succeeded in 

 giving to rhodium a high density, by fusion before his oxy- 

 liydrogen blow-pipe. In an obliging communication to the pre- 

 sent annotator, this gentleman states, that " Dr. WoUaston's 

 own rhodium, taken from the pure specimen he gave me, is ren- 

 dered perfectly malleable before the gas blow-pipe, and in this 

 niulleable state, after being hammered, its specific gravity, (es- 

 limuted in distilled water, at the temperature of 60° of Faren- 

 hcit,) equals 20.03, being as high as that of pure hammered 

 platinum." Dr. WoUaston's rhodium, fused in his own air-fur- 

 uaco, has a spccilic gravity of only 9.74 by our experiments. 



• F 



'/.(/. Tntnu. for 1804, page 423. 



