250 M. Baruel otj the Process 



last salts being very soluble, remain in the liquid with the 

 iron, but the atnmonio-muriates of platinum and iridium being 

 very sparingly soluble form the precipitate, which has a tawny 

 or reddish-yellow colour, of more or less depth, according as 

 the proportion of the salt of iridium is more or less considerable. 

 When the further addition of the muriate of ammonia produces 

 no more precipitate, the whole is to be thrown on a filter of 

 cotton, and washed with water of as great coldness as possible, 

 which is conveniently procured by putting a bit of ice into the 

 water intended for the washings. When the precipitate is suf- 

 ficiently washed, which is recognised by the water that passes 

 having merely a faint yellowish hue, it is to be dried. This 

 precipitate, as we have remarked, is an ammonia-muriate of 

 platinum, the pure yellow of which is altered by its mixture with 

 the ammonio-muriate of iridium, which is red. 



15. This impure ammoniacal salt of platinum is. calcined in 

 a crucible, observing to heat the crucible at first in its upper 

 part, in order to avoid the volatilization of a portion of the salt, 

 without its being decomposed. The heat is to be pushed to 

 redness, at which temperature it must be kept up for an hour. 

 By this means the salts are decomposed, and there remains in 

 the crucible only the platinum and iridium. To separate these 

 two metals we put them into a retort, and dissolve them anew 

 in the nitro-rauriatic acid ; but in this case the nitric acid must 

 be only at 28° (1.24), and the muriatic acid at 19° (1.15). Two 

 and a-half parts of this acid suffice to dissolve one of platinum 

 thus reduced, without affecting the iridium. This metal re- 

 mains at the bottom of the liquor (which is of a fine orange- 

 yellow colour,) under the form of a grey powder. On filtering, 

 pure iridium remains above, which is to be washed and dried. 



16. The solution of platinum must be precipitated once more 

 by muriate of ammonia; and the fine yellow ammonio-mu- 

 riate of platinum thus obtained, is to be reduced by strong cal- 

 cination in a crucible, observing the precautions already indi- 

 cated. The pure platinum remains in the crucible, under the 

 form of a greyish-coloured spongy mass, which acquires me- 

 tallic lustre by friction against any hard body. 



