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from the nature of the aquæ regiæ made use of, as froman over-proportion of sal ammoniac in the aqua regia inwhich the gold is dissolved, for sal ammoniac, as we haveformerly seen, is of itself sufficient to precipitate a part ofthe platina. Though I could not perceive any separationen mixing the two solutions, yet on diluting the mixturewith water, and suffering it to stand for some days, a brightgold coloured pellicle was thrown up to the surface : thatthis, however, was owing to the action of the platina, Iwill not affirm ; for I have seen a like separation from di-luted solutions of gold alone. Another mixture of solu-tions of gold and platina was evaporated a little, so as todispose it to shoot: it yielded first fine red crystals, whichseemed to contain chiefly gold, with very little platina jand afterwards deep saffron coloured crystals, in whichthe platina apparently prevailed.

XII. Platina, Silver , and Acids.

Platina, digested in a solution of silver made in aqua-fortis, was not at all acted upon, as indeed might havebeen expected, the platina not being soluble in the aciditself by this treatment. A plate of silver, digested in so-lution of platina, was strongly attacked : a white calx set-tled upon the silver, and incrusted it all over, and the platewas so corroded as to become friable between the fingers,the liquor still continuing of a gold yellow colour. Thisexperiment is from Marggraf: it seems to shew, that silverabsorbs the marine acid from solution of platina, and thatthe platina remains dissolved in the nitrous acid, for if anyof the platina had precipitated we may presume that the calxwould not have been white. He found, however, that whenthe silver was previously dissolved, either in the nitrous orvitriolic acids, it then occasioned a precipitation of the pla-tina, for on mixing these solutions with solution of platina-a yellow precipitate fell.