104 PHILOSOPHICAL TRANSACTIONS. [aNNO l/S/. 



contents, in bright yellow films, to the sides of the glass. Sundry other dis- 

 tilled 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 

 «ubtile fluid, prepared fi-om vinous spirits with the vitriolic acid, called by the 

 chemists aether. The separation succeeded in the same manner as before; the 

 aether 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 yield- 

 ing a sparkling red precipitate with volatile spirits, &c. A far more minute pro- 

 portion of platina, mixed with gold, is more distinguishable by these processes, 

 than by those with alkaline salts abovementioned ; these exhibitino the whole of 

 the platina dissolved by itself, those only a part of it. 



4. By Metalic Solutions. — All the metals, which precipitate gold from aqua- 

 regia, have been already shown to precipitate platina also. As gold is thrown 

 down by some metallic solutions, as well as by the metals in substance, particu- 

 larly those of mercury, and iron, it remains to apply these liquors as precipitants 

 for platina. 



1 . A saturated solution of mercury in aquafortis, which readily and totally 

 threw down gold in its metallic form, being added to a solution of platina, the 

 liquor became immediately turbid, and, on standing for a little time, nearly the 

 whole of the platina fell to the bottom. A solution of mercury in the marine 

 acid, or of corrosive sublimate, likewise precipitated platina, but less perfectly, 

 and with this difference, that the former precipitate was of a greyish brown co- 

 lour, the latter of a sparkling red. 2. Solutions of iron in the vitriolic acid, 

 or of common green vitriol in water, which totally threw down gold, happily 

 made no change in solutions of platina. Compositions of platina and gold being 

 dissolved in aqua- regis, the solutions diluted with about twice their quantity of 

 water, and a filtered solution of the vitriol gratlually added ; the mixtures in- 

 stantly grew turbid, and, on standing, deposited the gold in form of a purplish 

 grey calx, the whole of the platina remaining dissolved. It appeared, on nume- 

 rous repetitions of this experiment, that no part of the platina was precipitated 

 along with the gold, nor any of the gold kept suspended with the platina. 



