174 Process for procuring pure Platinum, Palladiim, &c. 
of the large proportion of oxide of osmium which it contains. It 
must be preserved in glass bottles, furnished with well-ground 
stoppers. 
12, The concentrated solution of platinum is to be diluted 
with from five to six times its weight of water, then filtered. 
13. The black powder which was not acted on by the nitro- 
muriatic acid, is also to be washed with water, dried, and kept 
in a phial; we shall distinguish it by the name of the dlack 
powder. 
14. Into the filtered solution we pour a saturated solution of 
muriate of ammonia, till this ceases to occasion any precipitate. 
In this operation there are formed ammonio-muriates of pla- 
tinum, iridium, rhodium, and palladium. These two last salts 
being very soluble, remain in the liquid with the iron ; but the 
ammonio-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 precipi- 
tate, 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 sufficiently 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 ammonio-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 yolatilization of a portion of the salt, with- 
out 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 cru- 
cible only the platinum and iridium. To separate these two 
metals we put them into a retort, and dissolve them anew in 
the nitro-muriatic 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 remains 
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- iDEN 
° 
