──────────────────────────────────────────────────────────────────────── CLASS IV.–METALLIC SUBSTANCES. ─────── OF METALS IN GENERAL. 225. METALS, in a perfect state, are easily distinguished from other minerals, by a peculiar brilliancy which pervades their whole substance, and which has the name of _metallic lustre_; by their complete opacity, and their great weight in proportion to that of other mineral substances. When taken from the earth they are found in one or other of the four following states: 1. In a native or metallic state, 2. Combined with sulphur, 3. In a state of oxide (21) 4. Combined with acid. Metals, when found in a state of combination with other substances, have the name of _ores_. They are in general deposited in veins (4), of various thickness, and at various depths in the earth. The mode of obtaining them is to penetrate from the surface of the earth to the vein, and there to follow it, in whatever direction it may lie. The hollow places thus formed are called _mines_, and the men employed in them are denominated _miners_. When the veins are at a great depth, or extend to any considerable distance beneath the surface of the earth, it is necessary, at intervals, to make openings, or _shafts_, to the surface, for the admission and circulation of the air; and also to draw off the water which collects at the bottom, by drains, pumps, or steam─engines, as the situation or circumstances require. After the metallic ores are drawn from the mine, they, in general, go through several processes before they are in a state fit for use. Some of them are first washed in running water, to clear them from earthy particles. They are then piled with combustible substances, and burnt or roasted, for the purpose of ridding them of the sulphur or arsenic with which they may happen to be combined, and which rises from them in a state of fume or smoke. Thus, having been freed from impurities, they undergo the operation of melting, in furnaces constructed according to the nature of the respective metals, or the uses to which they are to be subsequently applied. The knowledge of metals is a subject of great importance to mankind. Their use in trade is so frequent, and in the arts so various and so interesting, that few objects can be more worthy of attention than these. ──────────────────────────────────────────────────────────────────────── ORDER I.—MALLEABLE METALS; OR, SUCH AS ARE CAPABLE OF BEING FLATTENED OR ELONGATED BY THE HAMMER, WITHOUT TEARING OR BREAKING. ───────