[ $6$ ]

my experiments. The bead was dark coloured andrugged at top, white underneath, and retained a portionof the lead amounting to two or three parts in a hundred.He observes that the lead cannot, by common fire, beworked off clean from this metal, as it is from gold andsilver, on account of the platina not continuing fluid afterthe lead has been separated to a certain point; and judgesthat a sufficient heat for the complete separation of thetwo metals is not to be obtained by any other means thanby large burning glasses.

11. I have already observed, page 494, that platina di-vided by cementation with nitre, and afterwards purifiedby repeated sublimations of sal ammoniac, appeared no-wise different in cupellation from the common grains.Mr. Marggraf made trial of platina attenuated by solutionand precipitation. The orange coloured precipitate throwndown by fixt alcali from solution of platina in aqua regia,being well washed with hot water and ignited under amuffle, became brownish : nine parts of this matter weremelted with an ounce of pure granulated lead, and themixture exposed to the fire in a scorifying dish till a con-siderable part of the lead was scorified : the remainderworked in a cupel, left a rough bead, of a whitish greycolour, very brittle, perfectly like that obtained in the cu-pellation of crude platina : its weight was one grain. Theexperiment was repeated with a precipitate made with vo-latile alcali, and the event was the same. He tried alsothe powder which remained on distilling a solution of pla-tina to dryness ; this powder, calcined under a muffle, ac-quired a shining blackish colour, in which state thirty grainsof it were mixed with twenty times as much granulatedlead, and the mixture worked as above, first on a scorify-ing dish and afterwards in a cupel: the lcoriæ were of ablack-brown colour : the cupelled bead was brittle and. of

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