322 Professor Faraday on Platinum. [Feb. 22, 



The platinum has usually been obtained from these ores (after they 

 have been well washed, sifted, and mechanically separated) by the action 

 of nitro-muriatic acid; which, bringing the platinum into solution, 

 supplies a fluid which, on the addition of muriate of ammonia, &c., 

 throws down a precipitate of ammonio-chloride of platinum. This, 

 washed, dried, and heated, gives spongy metallic platinum ; which 

 being then pressed, heated, and hammered, yields massive platinum ; 

 the aggregation of the particles taking place entirely by adhesion and 

 welding. Instead of forming a solution by acids, Deville proposes to 

 employ a heat fluxion process ; and instead of welding, to fuse the 

 metal together at the last by intense heat, obtained by the use of the 

 oxy-hydrogen or the oxy-coal-gas blowpipe. The ore, properly prepared, 

 is mixed with its weight of galena, or native sulphuret of lead, and 

 half its weight of metallic lead ; it is then heated and well stirred 

 together, the iron and some other metals are taken up by the sulphur 

 of the galena, the platinum and other metals are taken possession of by 

 the lead, and when the action is well effected, the access of air is 

 adjusted until the remaining part of the sulphuret is decomposed, and 

 only platiniferous lead left at the bottom part of the crucible or furnace, 

 with scoriae upon it. The former is separated, and then heated, exposed 

 to air until much of the lead is oxidized ; which, escaping as litharge, 

 leaves at last an alloy of lead and platinum, containing not more than 

 10 or even 5 per cent, of lead. Such an alloy of platinum requires a 

 very high temperature to fuse it, and this is therefore attained and 

 applied in furnaces constructed of chalk-lime, heated by the insertion 

 of gas blowpipes. The heat first melts the alloy, and being combined 

 with oxygen in a little excess, the remaining lead is rapidly oxidized 

 and dissipated in fumes, and then being raised and continued, any gold, 

 copper, osmium, or other metals, except iridium and rhodium, are also 

 converted into vapour and driven oft'. The platinum remaining is at 

 last heated to a still higher degree, and is either cast into flat cakes or 

 granulated ; and this has been done with quantities weighing even as 

 much as 40 lbs. 



The resulting metal contains some iridium and some rhodium, 

 being in fact an alloy of platinum; but it is an alloy which being 

 harder than platinum, and even less liable than it to the chemical action 

 of acids and other chemical agents, is as useful as the pure substance 

 in the ordinary applications of the metal. As iridium and rhodium 

 have no employment at present better than that of alloying platinum, 

 thfeir quantity has been purposely increased until it has made as much 

 as 25 per cent, of the mass. 



A mixed process has been devised by MM. Deville and Debray, 

 which gives a platinum purer than any heretofore obtained. It is then 

 as soft and ductile as silver. But for this process, for general directions 

 and minute particulars, and for most interesting matter about all the 

 metals of the platinum group, the reader is referred to Volumes LVI. 

 and LXI. of the Annates de la Chimie, 



[M. F.] 



