VOL. L.] PHILOSOPHICAL TRANSACTIONS. 103 



guishable. 4. Many other experiments were made of the precipitations and 

 precipitates of gold and platina, by alkalies, both of the fixed and volatile kind. 

 The most remarkable effects were, that volatile alkalies added to both solutions, 

 in quantity just sufficient to saturate the acid, precipitated gold entirely, but 

 platina only in part, so much of it remaining suspended as to give the same 

 colour to the liquor as when fixed alkalies were made use of: that, on adding a 

 larger quantity of the spirit after the precipitation of the gold, the liquor became 

 yellow, a part of the metal being taken up again ; and that the platina was more 

 copiously redissolved, the liquor becoming of a deep brownish red: that the 

 washed precipitates of both metals, whether made by volatile or fixed alkalies, 

 proved soluble, by moderate digestion, in spirit of salt; those of platina much 

 more difficultly and sparingly than those of gold. 



3. By Iriflammable Liquors. — 1. Inflammable spirits, which revive gold from 

 its solutions in form of yellow films, have no such effect on solutions of platina. 

 This experiment affords not only a criterion for distinguishing with certainty 

 whether gold has been debased by platina, but likewise an infallible means of 

 recovering it perfectly pure from any admixture of that mineral. If the com- 

 pound be dissolved in aqua-regis, the solution mingled with twice its quantity or 

 more of the spirit, and the mixture suffered to stand for some days in a glass 

 slightly covered ; the whole of the gold arises to the surface, leaving the whole 

 of the platina dissolved. The golden pellicles may be collected, by pouring the 

 matter into a filter just large enough to contain it. The dissolved platina passes 

 through, leaving the gold on the paper, which is to be washed with fresh parcels 

 of water till the liquor runs colourless. The paper is then to be carefully squeezed 

 together, and burnt in a crucible previously lined with vitrified borax, when fully 

 sunk down, a little fresh borax is to be injected, and the fire raised to melt the 

 gold. The use of lining the crucible with borax is to prevent any moleculae of 

 the gold from lodging in its cavities. — This process is attended with one inconve 

 nience, the slowness of the separation of the gold from the solution ; this may 

 be in some measure expedited by employing a spirit, which has been distilled 

 from vegetables, that give over an essential oil. 2. As essential oils take up gold 

 from aqua-regis, and keep it dissolved for a time on 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 

 line yellow colour, and, on standing for a few hours, threw off great part of its 



