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some os them contract like oily or resinous fluids in theircongelation, or like clay in drying ; others expand, likecongealing water, or like plaster when it sets.

Mr. Smeaton found, in a set of curious pyrometricalexperiments, of which an account is given in the 48thvolume of the Philosophical Transactions, that from theheat of boiling water to freezing, a rod of zinc shrunknear three times as much as one of regulus of anti-mony ; yet, when the two metals were melted, the regu-lus of antimony seemed to shrink in fixing considerablymore than the zinc. This difference is the more remark-able, as among all the metallic bodies that have beentried, regulus of antimony in its solid state contracts orexpands the least, and zinc the most, by equal augmen-tations or diminutions of heat; whence the excellenceof this last for metalline thermometers, and other instru-ments whose effect depends on their length varying ac-cording to the degree of heat.

An elegant phenomenon of the contraction of silverin fixing is often observed at the end of the process of cu-pellation. When the silver remains fine on the cupel, ifthe vessel be drawn forwards from the heat, that it maycool somewhat hastily, the surface of the metal suddenlyfixing and contracting, squeezes out some of the fluid partwithin, which issues in little jets through different partsof the solid crust, and sometimes spirts up to a considera-ble height, hardening in the air as it rises. M. Morel,refiner of the mint at Paris, made several experiments oftin's vegetation as it is called, of which an abstract is givenin the French Memoirs for 1727: to cool the metal themore hastily, he applied a wet cloth to the surface, andat the same time dipt the bottom of the cupel in cold wa-ter, by which means he obtained larger and more nume-rous jets, variously arranged : he observes, that the larger

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