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when red hot they fly in pieces: they bear a good polish,and do not seem at all tarnished in keeping ten years; ofthe mixture of equal quantities in particular, the poliihedpart continues very brilliant. No.7. has tarnished a little,but seemingly not so much as pure copper.

Platina appears therefore from these experiments toharden copper, to dilute its colour, and diminish its dis-position to tarnish; in small proportions, to improve itshardness, without much injuring either the colour or mal-leability; and in larger proportions, to injure the mallea-bility less than it does that of any of the other ductile me-tals, except gold and perhaps silver. Platina and copperseem to form valuable compositions, of which I doubt notbut the workman may avail himself.

In a letter from Spain to a person in London, a trans-lation of which has been communicated to me, there is anaccount of an experiment on platina and copper, which,though imperfectly related, may deserve to be mentionedhere. The author first tried platina with an equal weightof silver, and found them to melt together .... he after-wards melted it with copper, which united perfectly well;but whether it was the platina itself, or the mixture withsilver, that was melted with the copper, is not clear fromthe words, though it seems to have been the former. Themixture with copper," on trying to hammer it, flew aboutlike glass; but having melted it over again with a strongerfire for some time, and thrown in a little saltpetre, mer-cury-sublimate, and other corrosives, it became malleable,and was then made into rings, which were worn for a goodwhile without soiling the fingers, and preserved alwaysthe same colour and lustre as those called in Spanishtombagos, which consist of two parts of copper and oneof gold."

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*A mixture