The modifications, to which particular bodies are subject, as to their respective effects, depend very greatly on the presence of other bodies, and frequently on the chemical action, which ensues throughout; so that, as we had occasion to observe, the _effect_ which one body would produce on the flame, maybe completely changed, modified, or varied by the presence of a second, third, or fourth substance. The art, therefore, of uniting various bodies, in kind, as well as in proportion, so as to produce a given effect, can be acquired only by a series of experiments. Zinc, as a metal, when finely divided, produces a peculiar effect; when mixed with other metals, and with certain salts, as sal ammoniac, another; and, when combined with some acids, as the carbonic in lapis calaminaris, a third effect; and these effects may be governed, as it appears, by the presence or absence of certain bodies. This fact will appear more striking, when we consider the various mixtures, and their respective properties. For the uses of zinc, see that article. _Sec. XLII. Of Zinc._ Zinc, commonly called spelter, is a metal, obtained from blende, or sulphuret of zinc, and calamine, or carbonate of zinc. The ore is first roasted, and then mixed with some carbonaceous flux, and submitted to the action of heat in close vessels. The metal is volatilized, and passes over, and is usually caught in water. It is then fused, and cast in moulds. Zinc possesses many remarkable properties, some of which are the following. It is of a brilliant white colour, with a shade of blue, and is composed of a number of thin plates, adhering together. Its specific gravity is more than six times that of water. It is brittle, but, when heated to 212 degrees, may be hammered out, or made into sheets. At 400° it becomes very brittle. Its tenacity is so feeble, that a wire of 1/10th of an inch in diameter, will support a weight of only 26 pounds. At 680° it melts, and above that temperature, evaporates. It soon oxidizes, and its lustre is therefore tarnished. At common temperatures, it soon decomposes water; and, when the vapour of water is passed over it at a high temperature, the decomposition is very rapid, the oxygen of the water being absorbed. Zinc is soon oxidized when melted and exposed to the air, forming a gray oxide. At a red heat, zinc inflames, and the product of combustion is the white oxide of zinc, or flowers. The oxide of zinc is reduced by mixing it with charcoal, and exposing the mixture to a strong heat in close vessels. Zinc will burn in chlorine gas, and forms a chloride of zinc. If the perchloride of mercury and zinc-filings be heated together, the same compound will result. This chloride melts at 212°, and rises, in the gaseous form, at a heat much below ignition. It was formerly called the _butter of zinc_, and muriate of zinc. With iodine, zinc forms a compound, called iodide of zinc.