All metals are simple bodies; that is to say, they cannot be made out of other substances, although two or more metals may be combined and be again separated, or they may be combined with numerous other substances, as oxygen, and also again separated. There are upwards of fifty metals known to chemists, yet but few are used to any extent in the arts or manufactures. All the metals in use for the very many purposes to which they are applied are not simple metals, but are what are called “alloys,” that is to say, compounds of two or more metals. The chief metals in use are-- IRON, MERCURY, COPPER, NICKEL, LEAD, GOLD, TIN, SILVER, ZINC, PLATINUM. But in the state of oxide many are used which are seldom seen in the metallic state, such are the earths and alkalies; and for colors, and several other purposes, many other preparations are in use. The chief alloys, or compound metals in use, are, brass, made of copper and zinc; pewter, made of lead and tin; bell metal and gun metal, made of copper and tin; and solder, which is a kind of pewter, and made of the same metals; the silvering for looking-glasses is made of mercury and tin; the gold and silver used for coin are not pure metals, but alloyed with two parts of silver or copper to every twenty-two of the pure metal, and this forms the “standard” gold or silver. The gold used by jewellers has often a much greater proportion of alloy--for this name is given both to a compound metal and the cheaper metal made to combine with the more precious. The object gained by thus alloying the coinage, is that of rendering the metals harder, so that they shall not suffer much loss in wearing; thus a small quantity of copper mixed with either gold or silver, renders them both harder, although itself softer than either. The combination of certain metals forming alloys, is often not exactly the mean of their respective qualities, for instance, a small quantity of silver is sometimes fused with cast steel for penknife blades, and although the silver is itself much softer than the steel, yet the combination is found to be both closer in the grain and harder; it is known as silver-steel in commerce. Bismuth, although itself not very fusible, increases the fusibility of other metals; a combination of 2 parts tin, 3 lead, and 5 bismuth, forms a metal fusible by boiling water. IRON. Illustration: NATIVE OXIDE OF IRON.