In the construction of the temple by Solomon, 130 years before the æra of Lycurgus, iron was employed in great abundance; and, from the cost lavished upon that building, we are almost warranted in considering it as still bearing a high value, even in that country, so far in the advance of Greece in the arts of civilized life.
Herodotus ascribes the discovery of the art of welding iron to Glaucus of Chio, 430 years before the Christian æra. But, before this period, the Greeks had carried the art of working it into Italy, Spain, and Africa; and the famous mines of Elba, that are still worked, were probably opened 700 years before Christ.
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.
When wrought iron is nearly pure, it has, when in bars of not less than an inch square, or plates not less than half an inch in thickness, a granular structure. From the appearance of these grains, an estimate may be had of its quality; grains without any determinate form, neither presenting, when broken, crystalline faces, nor arranging themselves in plates; and which, in the fracture of the bar, exhibit points, and even filaments, manifesting the resistance they have opposed, are marks of the best quality. If, when broken, a crystalline character is exhibited, the quality is bad, and will, according to a disposition difficult to describe in words, either break under the hammer when heated, or be subject to rupture when cold. These two opposite defects are, in the language of our manufacturers, called red and cold short, or shear. The former fault unfits it for being easily worked; the latter destroys its most important usefulness. When the manufacture has been badly conducted, crystals will appear mingled with tenacious grains, and a want of uniform consistence will render it unfit for being cut and worked by the file. Iron of the latter character may, notwithstanding, possess great tenacity.
In still smaller bars, good iron, in breaking, exhibits filaments like those shown by a piece of green wood when broken across; this is technically called nerve; and as it does not show itself in larger bars, it has been supposed that it is the result of the process of drawing out the bars. This is partially true, although the iron that presents a crystalline structure will not acquire nerve, however frequently hammered. To obtain nerve in larger masses, it is necessary to form them of bundles of smaller bars, a process known under the name of faggoting.