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XIV.. Precipitate of platina exposed to a burning ddHtave*Mr. Macquer and Mr. Baume, after examining theaction of a burning concave on crude platina, as alreadymentioned in page 466, exposed the red precipitate os pla-tina made by alcalies, to the focus of the fame burningmirrour. " It immediately begun to boil, and diminishedconsiderably in volume : there arose at the fame time a veryabundant and very thick fume, smelling strongly os aquaregia, and which appeared so luminous and so white inthe neighbourhood of the focus, that we could not decidewhether it was not a true flame: the precipitate at the sametime lost its red colour, to resume that which is natural toplatina, and it now had the appearance of metalline lace.Being continued in the focus, the white fume smelling ofaqua regia was succeeded by another fume or flame lesscopious, whose colour inclined to violet. A little timeafter, there was formed, in the hottest part of the focus, abutton of smooth brilliant matter perfectly melted, andthen the vapours ceased. Examining this button after itwas grown cold, we found it to be a vitrescent opake mat-ter, of a hyacinth colour on the surface, internally blackishand pretty compact. We dare not affirm that this was atrue vitrification of the platina in virtue of the saline mat-ters which were joined to it in the precipitate: the experi-ment ought to be repeated with pure platina, and with aburning glass or concave stronger than that we used." In-deed as the platina resumed its metallic aspect, it shouldseem to have been disengaged from the salts, before thetime that the vitrification begun; and perhaps a button ofblackish vitreous matter, formed in the middle of the focus,may be easily enough accounted for from the ferrugineouscalx, which the precipitate cannot be supposed to havebeen free from: see the experiments of the relation of pla-tina