It is from the working of these mines that we are to date the introduction of iron in such abundance as to reduce its price, bring it into general use, and finally cause it to supersede wholly the alloys of copper. This ore is of extremely easy reduction, by processes of great simplicity, which furnish iron of excellent quality, and are, as we shall hereafter see, still in use. We cannot, indeed, infer with certainty, that these were the processes used by the ancients; but their simplicity is a strong argument in favour of their remote invention. Steel seems to have been known as different in qualities from iron, at a very remote period; that is to say, it was understood that there were varieties of iron, which when tempered, became hard, whilst others remained soft. The intentional preparation of it, as a different species, seems to have taken its rise among the Chalybes, a people of Asia Minor, and it was afterwards obtained from Noricum. We still find in the latter country, (Styria,) an ore that furnishes steel, by processes as simple as those by which the iron is obtained from the ore of Elba, and hence can form some tolerable guess at the mode in which the steel of the ancients was obtained. The third form in which we find iron as an article of commerce, namely, cast iron, is of far more recent origin. It has been traced to the banks of the Rhine, and it is certain that stove-plates were cast in Alsace in A. D. 1494. From this epoch, then, dates the great improvement in the preparation of iron, by which its price has been so far lessened, as to render it available for innumerable purposes, from which a small addition to its present cost would exclude it. * * * * * Iron, as may be inferred from what has been stated, is known in commerce in three distinct forms--wrought or bar iron, cast or pig iron, and steel. The received chemical theory on this subject is, that the former is metallic iron nearly in a pure state, and that the two latter are chemical compounds of iron and carbon. How far this is true will be examined in the sequel.