Metal (Gr. ), a term including about 50 elementary substances which possess, either wholly or in part, certain well marked physical and chemical properties, of which the most universal and characteristic is lustre. The peculiar brilliancy and reflective power of the metals, which may be enhanced by polishing, results from their great opacity. The color of the metals is generally white with a grayish, bluish, or pinkish tint; copper and gold are the only exceptions. In extremely thin films some of the metals allow the passage of certain rays of light. Gold leaf transmits light of a faint greenish hue. Most of the metals have a high specific gravity, a property which was regarded as characteristic until the discovery of the alkaline metals, which are lighter than water. With the exception of arsenic, they may all be fused, the temperature required for fusion varying from 100° F. to the highest heat of the oxy-hydrogen blowpipe. Some of the metals may be volatilized. Mercury, the only liquid metal, is solidified at - 39° F. Arsenic when heated passes directly into vapor without fusion. Most of the metals possess a certain mobility of particles that allows of their being extended or otherwise altered in form.

The two nearly related properties of malleability and ductility, resulting from this, are not possessed by the metals in the same degree. A few of them, as antimony, arsenic, and bismuth, are decidedly brittle. Some assume a plastic condition before complete fusion, notably iron and platinum; on this property depends the operation of welding. The strength of the metals is very dissimilar, iron in the form of wire being about 26 times as tenacious as lead. They are all conductors of heat and electricity, although differing widely in this respect. The metals at present known, with the name of the discoverer and date of discovery of each, together with their atomic weights, are given in the following table:

With a few exceptions, the names and dates in the above list refer to the actual production of the metal. In many instances the metallic compounds were known and studied long before the metal itself was isolated. Some of the rarer metals have never been prepared in a pure form. Pelopium, formerly enumerated among the metals, has been shown to have no existence; and the existence of terbium is doubtful. The last four metals were discovered by means of the spectroscope. - The following tables exhibit the mutual relations of some of the more important metals in physical properties: