As a small portion of copper somewhat heightens the colour of pale gold, platina was melted with eight times its weight of standard gold made with copper alloy. The fusion was performed, as in the preceding experiments, in a close crucible, with a strong fire, but without any flux, and continued for about an hour. The metal appeared covered with a black scurf, and had lost about ⅟200. It was much duller coloured, harder to the hammer, and cracked sooner about the edges, than mixtures of fine gold with a larger quantity of platina. By repeated fusion, and frequent nealing, it became a little softer and tougher, so as to be drawn into pretty fine wire; but the colour was still exceeding dull, more resembling that of bad copper than of gold. The specific gravity of this compound was 17.915; a little less than the medium of the three ingredients unmixed, and a little greater than the mean gravity resulting from the platina by itself, and the copper and gold mixed; for copper, in the standard proportion, appears to diminish the gravity of gold more than it ought to do according to calculation. From the foregoing experiments it appears, that platina is miscible with gold, in certain proportions, without injuring either its colour or ductility, or occasioning any considerable alteration in the gravity: experiments related in former papers have shewn, that it stands aqua-fortis, and the other trials by which the purity of gold is estimated. It is to be hoped, that the abuses manifestly practicable by this mineral have hitherto been but rarely made use of. To guard against them is the object of this paper; to detect them, of the next. XX. _Experimental Examination of_ Platina. _By_ William Lewis, _M.B. F.R.S._ +PAPER+ VI. _Experiments of distinguishing and purifying Gold mixed with Platina._ [Read Mar. 31, 1757.] 1. _By Amalgamation with Mercury._ IN an experiment related in the fourth paper, an amalgam of one part of platina and two of gold with a suitable quantity of mercury, having been triturated with water for a considerable time, and occasionally washed over, the platina was gradually thrown out, and the gold retained by the quicksilver.