66 On the Purification of Platina. 
Instead of directly dissolving the ore of platina in the. 
acids, I begin by melting it with zinc*. The alloy is form- 
ed with facility, and even with an extrication of heat and 
light, as has been observed by Lewis. The heat produced, 
by a common reverberating furnace is sufficient for deter~ 
mining this combination. We must first heat the zine; 
and as soon as it is melted, gently pour the platina above it: 
we then cover the crucible, and increase the fire by placing 
the dome on the furnace, and adapting to it a pipe about a 
metre in height. Half an hour afterwards, if the mass be 
not very considerable, we take off the crucible: a part of 
the zinc is vaporized in this operation, and consequently it 
is lost ; but this is inevitable, if we wish to have a homoge- 
neous combination. 
The alloy which we obtain is of a garyish white, a little 
grained in its fracture, and very easily pulverized. We 
reduce it into fine powder, and attack it with the sulphuric 
acid diluted in two or three times its weight of water. 
When the action of the acid diminishes, we must restore if. 
by the help of heat; aud whem it ceases entirely, we decant 
the liquor and pour new acid on the residuum 3 we conti- 
nue in this manner until the acid no longer produces any 
effect. By operating in this manner we easily obtain sul- 
phate of zinc from the liquors first decanted ; the last may 
be reserved in order to attack new quantities of alloy. 
When the sulphuric acid alone exercises no: more action, 
we add a small quantity of nitric acid, which determines the 
solution of a new quantity of zinc. We may then employ 
a sulphuric acid more concentrated. Jn this last case it 
takes up a little platina and palladium, but we may recover 
these metals by the green sulphate of inon and sal ammonia, 
and afterwards purify the sulphate of zine with metallic 
zinc. 
When the acid can dissolve no more, we decant the liquor 
and wash the residuumt. It is then easily dissolved in the 
nitro-muriatic acidt. The proportion of the nitric and 
muriatic asids which appeared to me to be the most con-: 
venient, is that of one part of the former to three of the 
*J employed four parts of zinc to one of platina; but I am of opinion: that 
ihis proportion may be greatly diminished. 
+This'residue burns with’facility at a very slight heat; and even if we have 
employed a smaller proportion of zinc, the residue detonates like gunpow~ 
der. ‘The muriatic acid takes this property from. it. 
¢That which | obtained from an alloy of four parts of zinc and one of pla+ 
tina in grains, an alloy which by fusion had lost one part of the ginc, only 
required for its solution alittle more than four times the weight of the platina 
in gitro-muriatic acid. 
latter. 
