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XIV. Flat in a mtb metallic glaJJ’es.

Mr. Marggraf, after having satisfied himself thatplatina perfectly resists the common unmetallic fluxes ofthe vitreous and saline kind, as related in the fourth sectionof this history, proceeded to try if the more active glass oflead would serve as a flux for it.

A glass of lead, prepared from four parts of the finestminium and one part of pure flint, was reduced into pow-der and pasted through a fine sieve, to separate any metallicgrains that might remain in it. Eight ounces of the pow-der were mixed with one ounce and a half, or 720 grains,of platina, and the mixture urged with a strong fire, ina close luted crucible, for two hours : a white or grey-ilh brittle regulus was obtained, covered with a yellowistascoria. The regulus was remelted with more of the fameglass of lead, and kept again two hours in fusion : it look-ed as before, had a like yellow scoria, and weighed 606grains, or about a sixth part less than the platina employ-ed. Kept in fusion two hours in a close crucible, it lostsix grains, or about a hundredth part. It was then beatenin pieces in an iron mortar, and mixed with an ounce ofcommon green glass in fine powder : the mixture beingkept melted for three hours in a covered crucible, thescoria proved turbid, inclining to greenish, and in someparts to bluish; the metal had lost thirty grains, or abouta twentieth ; it filed well, looked very white in the marksof the file, had some toughness, and did not very easilybreak under the hammer. It was again exposed to a strongfire for two hours in a close crucible, with half an ounceof calcined borax: the borax run through the crucible,but the metal did not perfectly melt, only baking into amass, of an unequal rough surface, porous, easy to break,in the fracture of a grey and white colour intermixed, in

weight