It may be proper to observe, that by the processes here pointed out, the gold is purified from other metallic admixtures at the same time that it is separated from platina; the inflammable spirits reviving, essential oils and æther imbibing, and green vitriol precipitating, gold alone. Care should be had, that the piece of the mixt, taken for examination, be totally dissolved before any trials are made with the solution; the menstruum not acting with equal facility on the two metals, but dissolving the gold more readily than the platina. Where the acid has been dilute, and only a gentle heat applied, great part of the gold has appeared to be taken up before the platina was considerably acted on. Where the filter, with the gold in it, is burnt in the crucible, borax is the most commodious flux: but as this salt gives a sensible paleness to gold, a little nitre may be injected, after the metal has come into fusion, to restore its colour. If the nitre was added at first, whilst the gold continues subtilely divided, some particles of the metal would be dissipated during the deflagration, which that salt produces with the coaly remains of the paper. As the foregoing experiments exhibit platina and gold dissolved in a mineral fluid, which by simple mechanic agitation rejects the one and retains the other, and which discovers this different appetite of union so much the more remarkably, as the two metals have been the more intimately combined:--as they further exhibit platina dissolved in liquors incapable of holding gold suspended,--gold dissolved in liquors incapable of holding platina suspended,--gold totally precipitated by substances, which precipitate no particle of platina,--and gold, when mixed _per minima_ with platina, perfectly recovered from it by these means, without increase as well as without diminution:--it follows, that platina is not, as some believe, gold naturally debased by the admixture of some other metallic body, but a metal of a peculiar kind, essentially different from all the others. Before the discriminating characters of platina were discovered, such a notion was highly plausible, and direct experiment seemed to confirm it: a portion of the platina might be separated in the process; a quantity of gold mixed with the remainder, in order to collect the gold supposed to be contained in it; the mixture submitted to operations, which gold alone was supposed capable of withstanding; and the augmentation, which the noble metal still retained, held to be true gold gained from the platina.