for "procuring pure Platinum. 253 



acid excess ; then this is to be diluted with four or five times'its 

 weight of water, as cold as possible. Into this a solution of 

 muriate of ammonia is to be poured, till it ceases to occasion 

 a precipitate. What falls is an ammonio-muriate of platinum, 

 which must be separated by filtration. The solution is then 

 concentrated, and allowed to cool several times in succession, 

 to separate all the ammoniacal salt of platinum which it may 

 contain. When the liquid is completely deprived of platinum, 

 or when it yields no longer the yellow precipitate, we dilute it 

 with five or six parts of cold water; and it ought to have a sen- 

 sible excess of acid. This, if wanting, may be supplied by 

 adding a little of the muriatic. We then pour into it water of 

 ammonia, drop by drop, but not so much as entirely to saturate 

 the acid-excess. Immediately there is formed, in the liquid, a 

 precipitate in the shape of small needles, delicate and shining, 

 possessing a beautiful pale rose-colour. This crystalline pre- 

 cipitate is an ammonio-subprotomuriate of palladium. Since 

 this salt is insoluble, there can remain none of it in the liquid. 

 It may be separated by the filter, and washed with very cold 

 water. By heating this salt to redness in a crucible, the palla- 

 dium remains pure. It may be afterwards melted in a cavity of 

 ignited charcoal, on which a stream of oxygen gas is made 

 to play. 



20. The liquid freed from the salt of palladium, possesses a fine 

 currant-red colour, derived from the ammonio-muriate of rho- 

 dium, which it holds in solution, and which is very soluble. It con- 

 tains, moreover, a little muriate of iron, and occasionally a little 

 muriate of copper, when this metal has not been entirely dis- 

 solved by the first portion of nitro-rauriatic acid, which was 

 made to act on the ore, as has been stated above. There are 

 two modes of treating this salt, to obtain pure rhodium. The 

 first consists in evaporating this liquid, at a gentle heat, to dry- 

 ness ; and boiling the residuum several times along with abso- 

 lute alcohol. The spirit dissolves all the muriate of iron and 

 copper, with the excess of sal ammoniac, and does not affect 

 the ammonio-muriate of rhodium, which remains in the form of 

 a saline powder of a fine carmine>red colour By calcining this 



