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to enquire more satisfactorily into so curious a fact by arepetition of the experiment. The substance, by whichthe apparent degradation was produced, was a powderof unknown composition, communicated to Mr. Boyleby a stranger, and its quantity not sufficient for morethan a single trial. There was so very little of it, thathe could scarce see the colour of it, save that, as faras could be judged, it was of a darkish red : the quantitywas estimated at an eighth or a tenth part of a grain.The gold had been formerly English coin, and to be sureof its goodness, he caused it to be, by one whom heusually employed, cupelled with lead, and afterwardsquarted with refined silver and purged aqua fortis. Twodrams of this gold, thus purified, were weighed out,and put into a new crucible first carefully nealed, andthe gold being brought into fusion, without addition,he put into the well-melted metal the little parcel ofpowder with his own hand, continuing the sire about aquarter of an hour, that the powder might have time todiffuse itself every way into the metal: the well-meltedgold was then poured out into another crucible, whichhad been gradually heated to prevent its cracking.- Butthough, from the first fusion of the metal to the pouringout, it had turned in the crucible like ordinary gold,save that once, as the assistant observed, it looked for twoor three minutes almost like an opal : yet when the mat-ter was grown cold, though it appeared on the balancethat it had not lost any thing of its weight ■, yet, insteadof fine gold, there was a lump of metal of a dirty colour,and as it were overcast with a thin coat almost like halfvitrefied litharge : to one side of the crucible there stucka little globule of metal, that looked not at all yellowish,but like coarse silver ; and the bottom of the cruciblewas overlaid with a vitrefied substance, whereof part was

of