3.--_Report of the minority of the Select Committee on certain memorials to reduce the duty on imported iron._
4.--_Remarks of the majority of the Select Committee on the blacksmiths" pet.i.tion in reply to the arguments of the minority._
5.--_Manuel de la Metallurgie de fer par_ C. I. B. KARSTEN, _traduit de l"Allemand, par_ F. I. CULMAN, _seconde edition, entierement refondue, &c._ 3 vols. 8vo. pp. 504, 496, & 488.
Mme. Thirl: 1830: Metz.
6.--_Voyage Metallurgique en Angleterre, par_ MM. DUFRENOY _et_ ELIE DE BEAUMONT. 1 vol. 8vo. pp. 572. Bachelier: Paris: 1827.
The discussion contained in the pet.i.tions and legislative reports which we have prefixed to this article, is one of the most powerful interest, not merely to those concerned in the manufacture of iron, and the articles of commerce of which it is the material, but to the whole community. Iron, if the cheapest and most abundant, is intrinsically the most valuable of the metals. It may supersede, and gradually has, in its applications, superseded the greater part of the rest, and has taken the place of wood and stone in a great variety of mechanical structures; it is indispensable in the modern arts of the attack and defence of nations; and its possession is the distinctive difference between civilized man and the savage. Well was it said to Croesus exhibiting his golden treasures, that he who possessed more iron, would speedily make himself master of them, and the truth of the maxim was even more powerfully verified, when the acc.u.mulated riches of the Aztecs and Incas were acquired at the cost of a few pounds of Toledo steel.
When we compare the state of manners and arts of the Mexicans and Peruvians with that of their Spanish conquerors, we are almost compelled to admit, that the possession of iron was perhaps the only real superiority in civilization which the latter possessed. Gunpowder played but a small part in the contests where handfuls of men routed myriads; the courage of the Indian warrior is not less firm than that of the descendant of the Goths.
The sciences and arts which are now the boast of European civilization, were then but awakening from a slumber of ages; in the latter, the workmanship of Europe was in many instances inferior to that of the new world, and in the former, to take as an instance that which occupies the highest place, astronomy, the civil year of the Mexicans was intercalated and restored to the solar, by a process more perfect than that we even now employ; and the latter was not introduced into Europe until half a century after the throne of Montezuma fell. The b.l.o.o.d.y human sacrifices which excited to such a degree the abhorrence of the conquerors, were not greater marks of savage cruelty, than were their own _auto da fes_, and the tortures inflicted on Guatemozin. Yet if not superior in bravery, in the arts, the sciences, and the more distinctive attribute of civilization, humanity, the possession of iron was sufficient to ensure the triumph of the Spaniards.
Of all the metallurgic arts, that by which iron is prepared from its ores, demands the greatest degree of practical skill, and is the most difficult to bring to perfection. Although ages have elapsed since it first became an object of human industry, its manipulation and preparation are yet receiving improvements, while those of the other ancient metals appear hardly susceptible of modification or advancement.
Copper and its alloys, tin, lead, and mercury, were as well and as cheaply prepared by the ancients as by the moderns; and the reduction of the precious metals has received no important change, since the process of amalgamation was first applied to them,--while the preparation of iron is daily improving under our eyes, and its cost diminishing. It may even be doubted whether the iron we first find mentioned in history, was an artificial product, and not obtained from the rare ma.s.ses in which it is found existing in the native state, and which are supposed to be of meteoric origin.
The original use of iron is ascribed in the sacred writings to Tubal Cain, who lived before the flood;--but we have no proof that he did not employ a native iron of this description. Be this as it may, the united testimony of antiquity exhibits to us an alloy of copper used for the purposes to which we apply iron, and the latter metal as comparatively scarce, and of high value. The qualities of iron were known and appreciated, but the art of preparing it was not understood. The reason is obvious; those ores of iron which have an external metallic aspect, are difficult of fusion and reduction, those which are more readily converted, are dull, earthy in their appearance, and unlikely to attract attention,--while gold and silver manifest in their native state their brilliant characters, and the ores of copper and lead exhibit a higher degree of l.u.s.tre than the metals themselves.
If, then, history does not show us the ancient nations employing iron for their arms and instruments, it is because they were unable to prepare it. Even in the middle ages, we find copper in use for arms, because the nations that employed it, could not conquer the difficulties that attend the preparation of iron.
The books of Moses, however, show that iron was known at that era to the Egyptians, and the distinction he draws between it and bra.s.s, seems in favour of our view of the origin of that which was then employed. The stones of the promised land were to be iron, but bra.s.s was to be dug from the hills. Twelve hundred years before Christ, if we receive the testimony of Homer, who, if he be rejected as an historian, must still be admitted as a faithful painter of manners. The Greeks used an alloy of copper for their arms, but were unacquainted with iron, which they estimated of much higher value.
Autar Peleides thechen solon autochoonon, hon prin men riptaske mega sthenos eetionos.
Alla etoi ton epephne podarchos dios Achilleus, Ton d aget enneessi sun alloisin chteatessin.
Ste d orthos chai muthon en Argeioisin eeipen.
Ornusth, hoi chai toutou aethlou peiresesthe!
&c. Iliad, Book XXIII, 1. 826.
From this pa.s.sage and the following lines, we learn the two-fold fact: 1. That a ma.s.s of iron of no greater weight than could be used as a quoit, by a man of great strength, was esteemed of sufficient value to be cited as an important article in the spoil of a prince: 2. That its use was confined to agricultural purposes, and not applied in war. Hence the more valuable form steel, and its tempering, were unknown.
Five hundred years later, Lycurgus attempted to introduce the use of iron, as money, into Sparta. The reasons usually cited for this act, do not seem to apply; and we ought not to accuse that lawgiver of the want of knowledge in political economy that is usually ascribed to him, in endeavouring to give a base material a conventional value to which it was not ent.i.tled. The iron was still, probably, more costly than bra.s.s, and the error of Lycurgus did not lie in ascribing to it a value beyond its actual cost, but in depriving it of the property of convertibility to useful purposes, which was necessary to maintain its price.
In the construction of the temple by Solomon, 130 years before the aera 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 aera. 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 Noric.u.m. 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 ma.s.ses, it is necessary to form them of bundles of smaller bars, a process known under the name of f.a.ggoting.
Iron contains in its ores many impurities of different natures, according to circ.u.mstances, and is in its preparation exposed to several others; by these its quality is frequently much affected. Its valuable ores all contain the iron in the state of oxide. The oxygen, it is generally believed, is not wholly separated even in the best malleable iron, but enough still remains to impair in some degree its good qualities. In its manufacture it is exposed to the action of carbon, with which it is capable of combining. Much iron appears to contain some of the combinations of this sort, existing in the form of hard particles, technically known by the name of _pins_.
Of inflammable bodies, sulphur and phosphorus are frequently contained in the ores of iron; and when pit coal is used in the manufacture, the former substance is present, and may influence the product. The union of sulphur, in very small quant.i.ties, with the iron, creates the defect called red short, although it is probably not the only substance that produces the same fault; but when it is caused by sulphur, all the good properties of the iron are impaired, which is not always the case when it arises from other impurities. The defect of breaking when cold, has been attributed to the presence of phosphorus by high authority. There are, however, ores in this country, containing a phosphate of lime, which yield iron of excellent quality.
A mixture of sulphur and carbon deprives iron of its property of welding, and in the highest proportion gives the opposite defects of being both red and cold short.
Ores of iron contain the earths, silex, alumina, lime, and magnesia.
With the bases of these earths the metal is capable of forming alloys; those of the three first are often thus combined. Silicium has been discovered combined with iron to the extent of 3-1/2 per cent. It has been found to render this metal harder, more brittle, and more similar in structure to steel; so small a quant.i.ty as 1/2 per cent. has been sufficient to render it liable to break when cold; and it appears probable, that by far the greater part of the cold short irons owe this fault to the presence of silex, rather than to that of phosphorus. Iron obtained from the ores by means of coal, is, under circ.u.mstances of equality in other respects, more likely to be combined with silicium than when made with charcoal. Karsten infers that a combination with aluminum produces similar defects, and denies the a.s.sertion of Faraday, that the good qualities of a steel brought from India are due to an alloy with this earthy base. A combination with the metallic base of lime, lessens the property that iron possesses of being welded, but does not render it more liable to fracture, either under the hammer or when cold.
Of the metals proper:--
Copper renders iron red short.
Lead combines with iron with great difficulty, so that its presence in the ores can hardly be considered dangerous, but when the combination is formed, the iron is both liable to break when red-hot and when cold.
A very small quant.i.ty of tin destroys the strength of iron in a great degree when cold, but still leaves it fit to be forged.
Wrought iron does not appear to unite with zinc, but its presence in the ores is injurious to the manufacture, for a reason that will be hereafter stated.
Antimony renders iron cold short, the alloy is harder and more fusible, and approaches in character to cast iron.
a.r.s.enic produces a great waste in the manufacture of iron, and when alloyed with it, injures or destroys its capability of being welded.
Ores which contain t.i.tanium, according to universal experience in this country, give an iron inclining to the defect of red short, but possessing the highest degree of tenacity. Such are several of the ores of the northern part of New-Jersey, and of Orange County, New-York.
Manganese in small quant.i.ties renders iron harder, but injures none of its good qualities. Many of our ores contain manganese, but when carefully manufactured the iron appears to contain but an insensible trace of this _metal_.
Nickel unites with iron in all proportions, and gives a soft and tenacious alloy; no good property of the iron appears to be injured by it. United with steel it gives an alloy of excellent quality. Nickel is rare among the ores of iron that are not of meteoric origin. But native malleable iron is occasionally found in large ma.s.ses alloyed with this metal, and its extrinsic source has been fully ascertained. The ma.s.ses are sometimes of very great size; we have already expressed our opinion that the iron that first came into use was derived from this source, and had been employed for ages before the processes for preparing it from its more abundant ores were discovered.
Cast iron is distinguished into two varieties, which are obviously distinct in character, the grey and the white; a mixture of the two forms that which is called mottled. It is generally believed, and usually stated in the books, that both of these are combinations of iron with carbon, and that their difference in appearance and quality grows out of the difference in the proportions in which the two substances exist; that the grey iron contains the greatest dose of carbon, and the white the least. There is, as will be seen, good reason to question the latter part of this statement.
The grey iron requires the greatest degree of heat for its fusion, is more fluid when melted, is softest, best fitted for castings which require to be turned or filed, and for those that must be thin; the white iron is very hard and brittle; the greatest degree of strength and tenacity is due to the mixture, or mottled iron, and to that variety of mottled in which the grey rather predominates.
The different varieties are readily convertible, for the grey iron when melted and suddenly cooled becomes white, when cooled more slowly is mottled, and when carefully preserved from rapid loss of heat, retains its colour. On the other hand, experiments on a small scale have shown, that white cast iron, subjected to a heat equal to that at which the grey melts, and allowed to cool slowly, becomes grey. Hence their difference can hardly be ascribed to chemical const.i.tution. Neither can the presence of a greater or less quant.i.ty of oxygen, as is sometimes supposed, produce the difference, for under circ.u.mstances in all other respects similar, except the rate at which they are cooled, iron of the three different varieties may be produced, We therefore feel warranted in rejecting the usual theory, particularly as the reception of it has rather impeded than advanced the manufacture of iron.
The theory of Karsten is far more consistent with the facts, and is directly applicable to the practical purposes of the iron master. We shall endeavour to give a succinct exposition of this theory, introducing all that is necessary for its full explanation.
The ores of iron, which are all oxides, are reduced by exposing them to the action of carbonaceous matter, at a high temperature. The carbon first separates the oxygen from the ore, which becomes metallic, but as it has for the carbon a high affinity, that substance tends to combine with it. The iron combined with carbon is rendered far more fusible than it is when pure, and thus readily melts; when the heat of the furnace is little more than is sufficient for effecting this fusion, the two substances are uniformly mixed, and probably form a compound a.n.a.logous to a metallic alloy; this is the white cast iron. When the compound is exposed to a heat higher than is sufficient to melt it, a separation appears again to take place, the carbon tending to a.s.sume in part the form of plumbago, the iron to retain no more of carbon than is sufficient to keep it liquid at the new temperature, and thus pa.s.ses from the state of cast iron to that of steel, and finally approaches to that of malleable iron. If the cooling take place slowly, the carbon, obeying its own law of crystallization, arranges itself in thin plates, and the iron, consolidating afterwards, fills up all the interstices with grains or imperfect crystals; and thus the ma.s.s a.s.sumes a dark grey colour, partly owing to the natural colour of the iron, but in a greater degree to the plumbago. When the cooling is rapid, the carbon still disseminated throughout the ma.s.s, does not crystallize separately, but the two substances again form an uniform compound.
Thus, according to the theory, there is no essential difference in the proportion of carbon between grey and white cast iron, but the former is a mechanical mixture of crystals of carbon, nearly pure, with iron containing a less proportion of carbon than the white, while the white iron is a h.o.m.ogeneous alloy of carbon and iron.
Upon this theory may be explained all the facts which have been found wholly irreconcilable with the other.
1. The more intense the heat of the furnace, the deeper the colour, and consequently the higher quality of the cast iron.