*

L 5 8 7 ] ^

one another, being rendered miscible by the interventionof nickel: that when this mixture is again melted withglass, the cobalt-regulus vitrefies first ; the nickel, moredifficultly calcinable or vitrescible, preserving its metallicform to the last. It may be presumed therefore that theoperations, which Marggrafs metal passed through, sepa-rated the true cobalt-regulus, and left only the nickel.

XI. Plat in a, Gold , and Aqua regia.

Into a saturated solution of platinamade in aqua regia,Mr. Marggraf put a plate of fine gold, and digested thewhole in a moderate warmth for some days : the gold wasnot in the least acted upon, and there was no precipitationof the platina, except that a little dark orange colouredcrystalline powder settled to the bottom, which the solu-tion of platina would have deposited by itself. The purergrains of platina were treated in the fame manner with asaturated solution of gold, and with the same event, theacid shewing no disposition to quit either of these metalsin order to attack the other, so that its affinity seems to beequal to both. I melted the two metals together, and di-gested the compound in aqua regia : the menstruum dis-solved them both, but the gold most readily; for the firstportion of the liquor having been insufficient to dissolvethe whole of the mass, and the rest being digested in freshaqua regia, the first solution was found to have the greatestproportion of gold, and the other of platina. When thequantity of gold was such, as to give any thing of a goldcolour to the mixture, the acid soon made the plates white,by eating out the gold first. I likewise mixed togethersolutions of the two metals, and did not observe any tur-bidness or precipitation to ensue, though Mr. Marggraffound, in his repetition of this experiment, a reddish orangecoloured precipitate : in this respect variations may happen

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