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fires, so strong as almost instantly to melt off a piece ofthe end of the forged iron rod with which the fuel was attimes stirred down. The platina still came out unmelted,and unaltered in its form; except that there were some-times a few globular drops like those mentioned in thepreceding article.

VII. Platina exposed, to a burning glass.

After all these fruitless attempts for the melting ofplatina, no other resource remains, for determining itsfusibility or non-fusibility, than the action of large burningglasses or concaves; a trial which I have often regrettedthat I could not in this country find means of exposing itto. What has earnestly been wished for by all those,whom profit, curiosity, or science, have interested in thesekinds of pursuits, Mr. Macquer and Mr. Baume haveendeavoured to supply.

They used a concave of plate glass, well silvered, twentytwo inches in diameter, and of twenty-eight inches focus.Before they proceeded to try its effects on platina, theyexposed to its action several other bodies, that some judge-ment might be formed of its force.

Black flint, powdered to prevent its crackling and flyingabout, and secured in a large piece of charcoal, bubbledup, and run into a transparent glass in less than half aminute. Hessian crucibles, and glasshouse pots, vitrefiedcompletely in three or four seconds. Forged iron smoked,melted, boiled, and changed into a vitrescent scoria, assoon as it was exposed to the focus. The gypsum ofMontmartre, when the flat sides of the plates or leaves,of which it is composed, were presented to the glass, didnot shew the least disposition to melt; but on presenting atransverse section of it, or the edges of the plates, it meltedin an instant, with a hissing noise, into a brownish-yellow

matter.