On the Purification of Platina. 67 
Jatter. T ought to observe, that there is a great advantage 
in not making the mixture before employing them. It is 
best first to pour the nitric acid on the metal, and after- 
wards gradually add the muriatic acid, until this addition 
does not producé any effect. It is also advantageous to 
émploy the acids in small quantities, by decanting the solu- 
tion before pouring in new nitric acid. 
After, the solution 1s terminated, we allow the liquor to 
test some time in a high vessel of a small diameter. When 
itis very clear, we decant it with a narrow syphon, in order 
to separate the black powder which remains after the solu- 
tion of the platina, and evaporate the liquor to perfect dry~ 
ness. If we afterwards dissolve the residue in a small 
uantity of water, and allow it to rest for 24 hours, almost 
thé whole of the gold which was contained in the ore is de- 
osited at the bottom of the vessel in the metallic state. 
€ decant again ; and if we wish to obtain the last portions 
of palladium, we add to the liquor a little prussiate of mer- 
euty, which, according to Dr. Wollaston, precipitates this 
metal completely. We then filter, and pour into the solu- 
tion pure carbonate of soda, until the precipitate which is 
_formed no longer increases; the effect of this addition is 
to forma triple salt of soda and platina, which, according to 
M. Proust, is not decomposed by the carbonate of soda 
added in the proper proportion, while the iron is precipi- 
tated. We separate this last by the filter, or, what is pre- 
ferable, allow it to rest, and then decant it; we wash the de- 
posit several times, and mix the liquors; but as the last 
washings contain very little platina, we may put them aside 
in order to precipitate the metal from them by sulphuretted 
hydrogen, or by a hydro-sulphuret. The roasted precipt- 
tate may afterwards be treated with the crude ore in a sub- 
sequent operation. 
If we are afraid that the ferruginous deposit does not re- 
tain any platina, we may ascertain it by dissolving a small 
portion in concentrated muriatic acid, and by adding to 
thé solution muriate of ammonia. If the triple salt which 
is deposited seems to be abundant, we treat the whole of 
the ferruginous deposit in the same manner. 
The liquor which contains the triple salt of platina and of 
soda ought to be slightly acid. We must add to it car- 
bonate of soda until it becomes distinctly alkaline. On 
Jeaving it exposed for some time to the air, the iridium 
would be separated in the form of a green sediment; but 
in order that this separation may take place more ine 
E@ an 
