METALS. The great characteristio of these well known substances Is their lustrous appearance; it is indeed so constant an accompaniment of them ea to afford, under the name of metallic lustre, a standard of deacriptlon for the appearance of other bodies.
Metals, In the common acceptation of the term, are either compound or simple. Bram, bronze, britannia metal, 8:c., are examples of compound metals; that is, they are composed of two or more simple metals. Compound metals are, however, always distinguished as ALLOTS, and hence the word metal Ls correctly, though not invariably, applied only to the simple or elemental metals.
The metals or metallic elements are considerably greater in number than the non-metallic elementary bodies, or metalloids. Including one or two concerning whose metallic character there is n little doubt, the whole number is about forty-nine. Very few of them occur naturally in the free or uncoinhinel state, being generally associated with non metallic elements, constituting errs. Some of them are obtained with such difficulty that they are very rarely met with, existing only in the cabinets of the endows, or perhaps exclusively tnet with iu the labora tories of the chemists who succeeded in isolating them. Several of them, however, FOCil as gold, silver, copper, iron, lead, tin, and mercury, have been known from the moat remote ages, and nearly nil the re t are well known to chemists.
The phyaical characters of the metals, including colour, relative lustre, ductility, malleability, tenacity, relative brittleness. hardness, elasticity, sonorousness, structure, power of conducting heat and elec tricity, melting point, and volatility, have already been described under METALS, in the NATFRAL HISTORY DIVISION of thiaCyclopiedia. Their condition and distribution in nature is also there dwelt upon, and the action of metalloids upon them cursorily noticed. The methods of separating them from each other have been given in the present division of the work, under CHEM tem, ANALYSIS ; and it now, therefore, may remains to detail the varieties methode of classification that con venience or analogy has induced chemists and physicists to adopt.
The special characters of the metals ; their farther relation to, and action upon, one another ; the action of metalloids, acids, tke , upon them individually ; and the formation, properties, use, &c., of their compounds, will be found described under their respective names, with the exception of iron, which we shall now proceed to describe.
Iron (Fe). In combination with other bodies, iron is perhaps more widely diffused than any of the metals. It is found in the ashes of nearly all plants, is a constant constituent of the blood of the vertebrate animals, and although only a few of its ores are economically made use of, they are more numerous than those of any other of the heavy metals. Paw, in NAT. HIST. DIV.] The range of affinities of iron is so great that it is very rarely met with in the uncombined state, and it is only with considerable difficulty that it can be artificially obtained in an absolutely pure condition. The process recommended by Berzelius for preparing chemically pure iron consists in heating filings of the best bar iron with pure oxide of iron under a layer of powdered green glass in a Hessian crucible : the whole being subjected to the highest tempe rature of a smith's forge, the filings are deprived of their carbon and silicon by the oxide, and fusing together collect at the bottom of the crucible in a button possessing silver-like lustre and whiteness. Iron thus prepared has a specific gravity of 7.8439, and is very tough and much softer than the ordinary metal. Another method of procuring perfectly pure iron is by passing a current of hydrogen gas over pure peroxide of iron, heated carefully to redness : if the temperature is too low the resulting product inflames spontaneously on coming in contact with the air, but when prepared at a higher temperature may be kept unaltered ; in this state it is sometimes used in medicine, under the name of Qucrennes iron, Per reduit, or Pelvis fern.