2. As essential oils take up gold from aqua-regis, and keep it dissolved for a time upon the surface of the acid; a pure colourless oil, that of rosemary, was poured into about half its quantity of a solution of platina, the mixture well shaken, and suffered to rest: the oil quickly arose, without taking up any thing from the platina, or receiving any colour: the acid liquor underneath remained coloured as at first. Compositions of platina and gold being dissolved in aqua-regis, and treated in the same manner, the whole of the gold was imbibed by the oil, and the whole of the platina remained dissolved in the acid. The oil, loaded with the gold, appeared of a fine yellow colour, and, on standing for a few hours, threw off great part of its contents, in bright yellow films, to the sides of the glass. Sundry other distilled oils were made trial of, with the same event. The gold is easily recovered, by setting the oil on fire; and, when thoroughly burnt out, melting the residuum with borax, as in the preceding experiment. After the separation of the oil employed at first, it may be proper, for the greater security, to add a little more; which, if any part of the gold should happen to have been left in the liquor, will effectually take it up.
3. The experiment was repeated likewise with the subtile fluid, prepared from vinous spirits with the vitriolic acid, called by the chemists æther. The separation succeeded in the same manner as before; the æther receiving nothing from pure platina, but instantly taking up the gold from a mixture of the two. It is observable, that the gold imbibed by this fluid is kept permanently dissolved by it; without separating or reviving, as it does from the common essential oils and vinous spirits.
4. The liquors remaining in these experiments, after the extraction of the gold, appear on all trials the same with the common solutions of platina; and readily betray their being impregnated with that mineral by their colour, by the precipitation with tin, by their yielding a sparkling red precipitate with volatile spirits, _&c._ A far more minute proportion of platina, mixed with gold, is more distinguishable by these processes, than by those with alkaline salts above-mentioned; these exhibiting the whole of the platina dissolved by itself, those only a part of it.