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spongy lump, which retained particles of the flux hereand there in its cavities, a mark that it had not flowed thin.

It appears upon the whole, that platina does melt witharsenic, but less perfectly than with other metals; andthat it would be very difficult, if not impossible, to bringit, on this foundation, to sufficient fusion for being pouredinto a mould.. All the arsenicated pieces are very brittle,internally of a greyiffi colour, and a loose granulated tex-ture. It is observable that though arsenic soon changes inthe air to a blackiffi hue, and when mixed with othermetals disposes most of them to change in like manner,the arsenicated platina, after lying in a dry room for sevenor eight years, continues nearly of the fame appearance asat first.

VI. Platina with Zinc.

For uniting zinc with platina, 1 first tried the methodin which zinc is commonly united with copper, and bywhich the zinc is at the fame time purified from suchother metallic bodies as are frequently blended with it;viz. exposing the platina to the fumes, extricated by fireand inflammable additions, from calamine, one of thepurer ores of zinc. But that these fumes might actthe more effectually on the platina, a little variation wasmade in the common manner of disposing the materials.

Four ounces of calamine in fine powder were mixedwith two ounces of powdered charcoal. Having oftenobserved that calamine, with this proportion of charcoal,acquires a kind of fluidity in the fire, so that the platinawould be apt to sink through it to the bottom; I madethe powder into a mass with a little thin tempered clay,and pressed it into the bottom of a crucible: above thismass, the crucible was lined all round with luting to aconsiderable thickness, so as to leave only a small passagein the middle for the fumes of the zinc to issue out; in

which.