Αυταρ Πηλειδης θηχεν σολον αυτοχοωνον,Ον πριν μεν ριεπτασε μεγα σφενος Ηεβιωνος.Αλλα ητοι τον επεφνε ποδαρχος διος Αχιλλευς,Τον δ αγετ εννηεσσι συν αλλοισιν χτεατεσσιν.Στη δ ορθος χαι μυθον εν Αργειοισιν εειπεν.Ορνυσθ, οι χαι τουτου α εθλου πειρησησθε!
&c. Iliad, Book XXIII, 1. 826.
From this passage and the following lines, we learn the two-fold fact: 1. That a mass 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 entitled. The iron was still, probably, more costly than brass, 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 æra of Lycurgus, iron was employed in great abundance; and, from the cost lavished upon that building, we arealmost 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 ofnot 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.
Iron contains in its ores many impurities of different natures, according to circumstances, 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 ofpins.
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 quantities, 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 quantity 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 circumstances 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 assertion 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 quantity 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.
Arsenic 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 titanium, 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 severalof the ores of the northern part of New-Jersey, and of Orange County, New-York.
Manganese in small quantities 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 thismetal.
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 masses alloyed with this metal, and its extrinsic source has been fully ascertained. The masses 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 constitution. Neither can the presence of a greater or less quantity of oxygen, as is sometimes supposed, produce the difference, for under circumstances 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, particularlyas 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 analogous 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 assume 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 passes 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 mass assumes 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 mass, 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 homogeneous 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.
2. The changes that take place from grey to white cast iron, merely by difference in the rate of cooling.
3. The reconversion of the white variety into grey, by simply heating it above its melting temperature, and allowing it to cool gradually.
4. The formation of imperfect crystals of plumbago (kish) on the surface of grey iron.
5. The approach to malleability of the grey iron, which is utterly irreconcilable with its being a homogeneous compound, more charged with carbon than the white.
The basis of white cast iron, appears to be a definite chemical compound, of two atoms of iron to one of carbon, and is therefore analogous in its chemical constitution to carburet of hydrogen and carburet of sulphur, but like all metallic alloys it is capable of containing an excess of one of the substances in a state of mixture during fusion, and which does not separate on rapid cooling. The iron alone is found in excess in this substance.
Steel appears to contain but half the quantity of carbon in its chemical proportions that white cast iron does, but, like it, is susceptible of a variety of mixtures; if the proportion of carbon amount to three per cent., it loses the property of malleability, if the proportion fall as low as one per cent. it can no longer be tempered, and is identical with the harder varieties of bar-iron. As the carburets of iron, whether in the form of pig or of steel, may be considered as alloys, if they be presented to other metals, the results must necessarily be different from what occurs when pure iron is exposed to the same substance. The union that may take place in the one instance may not occur in the other. It may often happen, that when the iron is pure, a true chemical combination will occur, while in the other case, no more than a mechanical mixture can be effected. For the same reason, the consequence may be totally different when the third substance is presented to the iron when first deoxidated, in the presence merely of an excess of carbon, and when the combination with that substance has actually occurred.
If reduced at the same time with the iron, the other metals will unite with it more readily than with the carburet, and they may afterwards prevent its union with carbon, for there are few, if any metals, besides iron, which have any affinity for carbon.
Cast iron may contain the bases of the earths that form a part of its ores. Of these, silicium is the most usual, and there is probably no cast iron that does not contain a portion of it. It appears to render this form of the metal harder and less suitable for the purposes of the moulder, but is separated almost wholly when it is converted into wrought iron.
We have seen a parcel of pig iron that was marked with a species of white efflorescence, ascertained on examination to be silica; this was rejected for its hardness by the founder, but on being manufactured by the process of puddling, gave bar iron of good quality.
From what has just been stated, it appears that the other metals more generally exist in cast iron, in a state of alloy with pure iron, which is intimately mixed with the carburet. Thus as a general rule, the pig which contains them, will be morelikely to be grey in colour than that which does not, but it may, notwithstanding, be injured in quality. The exact effect of such alloys upon cast iron, does not appear to have been fully examined.
The ores whence iron is obtained, are all oxides, with the exception of a carbonate whence steel is in a few places obtained directly. They contain, in combination with the iron, or forming parts of a heterogeneous aggregate, a variety of earthy substances. In the reduction of these ores, two objects are to be accomplished, the separation of the oxygen, and the fusion of the earthy mass. Carbon, in some one of its native or artificial forms, is used to effect the former purpose, upon the same principle that it is applied to the other metallic oxides. Thus a furnace in which a fire of carbonaceous matter is kept up and urged to the highest possible degree of intensity by blowing machines, is necessary. When the earths are pure, even the highest heat of furnaces is incapable of fusing them, and although the oxides of the ancient metals, and among the rest, the oxide of iron, increase the fusibility of one of the earths; still, if but one earth be present, it is only in a few cases that the simple ore will furnish the means of its own fusion. We are therefore compelled to make use of the property possessed by the earths, of rendering each other more fusible.
Silica is the earth to which we have referred, as being susceptible of fusion when mixed with the oxide of iron. Silica, also, when mixed with the other earths, renders them more fusible than is its own mixture with oxide of iron. Hence it may be stated as a general rule, that ores which do not contain silica, cannot be decomposed without the addition of that earth. The most of our American ores contain silex in sufficient abundance; hence it is usual to add to them, in the process of reduction, carbonate of lime, which is calledflux. Did not the ore contain silica, this would not produce its effect, and a due admixture of the three earths, silica, alumina, and lime, appears to be necessary to cause the most advantageous results.
The remarks of Karsten on this head are new and worthy of attention.
"It is upon the choice and the just proportion of the flux, that the profit of the manufacturer in a great degree depends. Employed in too greatquantitiesthey fail in the important purpose of giving to the scoriæ a proper consistence. It is very difficult to fix their proportions exactly, and, in truth, these ought to vary with the manner in which the furnace works; but a proportion determined for a state of the furnace when the temperature is neither too high nor too low, is usually adopted."Chemists and metallurgists, have endeavoured to determine the degree of fusibility of the earths when mixed with each other; but their researches have shed but little light upon the management of blast furnaces. We are, in spite ofthem, still compelled to have recourse to experience. Far, however, be it from me to depreciate the attempts of Achurd, Bergman, Chaptal, Cramer, &c.; they are valuable at least, in pointing out the road that is to be pursued in the experiments."It follows, in general terms, from these experiments, that lime, silica, alumina, and magnesia, are infusible when not mixed with each other; that no mixture of earths is fusible without the presence of silica; that the fusion of the oxides of iron cannot take place by the addition of any simple earth other than silica; that ternary mixtures are more fusible than binary; that quaternary mixtures vitrify even more readily, and that the oxide of manganese promptly determines the liquefaction of all the earths."The theory of the vitrification of oxides, aided by trials on a small scale, points out the kind of earthy mixture which ought to be employed, but it cannot fix the exact proportion of the different earths that ought to be adopted; nor does it teach the means of replacing an earth by its chemical equivalent, as, for instance lime, by magnesia. The solution of the question will depend rather upon the properties of the silicates of lime and magnesia at high temperatures, than upon the action of these silicates upon iron. It is hardly probable that the iron obtained from all ores, could be equally good, even if the most proper fluxes could be added to these ores. Those who have maintained this opinion, have erroneously imagined that the reduction of the ore could always be effected under the same circumstances, which would not be the case, even if these fluxes were ascertained and made use of."
"It is upon the choice and the just proportion of the flux, that the profit of the manufacturer in a great degree depends. Employed in too greatquantitiesthey fail in the important purpose of giving to the scoriæ a proper consistence. It is very difficult to fix their proportions exactly, and, in truth, these ought to vary with the manner in which the furnace works; but a proportion determined for a state of the furnace when the temperature is neither too high nor too low, is usually adopted.
"Chemists and metallurgists, have endeavoured to determine the degree of fusibility of the earths when mixed with each other; but their researches have shed but little light upon the management of blast furnaces. We are, in spite ofthem, still compelled to have recourse to experience. Far, however, be it from me to depreciate the attempts of Achurd, Bergman, Chaptal, Cramer, &c.; they are valuable at least, in pointing out the road that is to be pursued in the experiments.
"It follows, in general terms, from these experiments, that lime, silica, alumina, and magnesia, are infusible when not mixed with each other; that no mixture of earths is fusible without the presence of silica; that the fusion of the oxides of iron cannot take place by the addition of any simple earth other than silica; that ternary mixtures are more fusible than binary; that quaternary mixtures vitrify even more readily, and that the oxide of manganese promptly determines the liquefaction of all the earths.
"The theory of the vitrification of oxides, aided by trials on a small scale, points out the kind of earthy mixture which ought to be employed, but it cannot fix the exact proportion of the different earths that ought to be adopted; nor does it teach the means of replacing an earth by its chemical equivalent, as, for instance lime, by magnesia. The solution of the question will depend rather upon the properties of the silicates of lime and magnesia at high temperatures, than upon the action of these silicates upon iron. It is hardly probable that the iron obtained from all ores, could be equally good, even if the most proper fluxes could be added to these ores. Those who have maintained this opinion, have erroneously imagined that the reduction of the ore could always be effected under the same circumstances, which would not be the case, even if these fluxes were ascertained and made use of."
Most of the ores of iron require, before they are subjected to the process of reduction, a preparatory operation called roasting. Thisconsistsin exposing them to a comparatively low heat. The more important use of this process is to render the mass more susceptible of mechanical division, but it also serves in many cases to separate the sulphur and arsenic that may exist in the ore. There are some ores, as, for instance, those of a number of mines in Morris and Sussex counties, New-Jersey, which are so free from impurities, and which yield so readily to the mechanical means employed for separating them, that this process is wholly unnecessary; but such ores are rare, and the process of roasting must, generally speaking, be performed.
The mechanical division, which exposes a larger surface to the action of heat and of the chemical agents, is called stumping; this is usually performed by appropriate machinery, but was in the infancy of the art effected by hand.
The reduction of rich ores of iron, such as are almost wholly made up of its oxides, and contain but little earthy matter, may be performed in a common smith's forge. The reduction in this case takes place immediately in the blast of the bellows, where the intensely heated ore is in contact with the burning charcoal; and if a carburet be formed, it is immediately decomposed, and pure iron is the result. Such is probably the more ancient of all the processes for obtaining malleable iron, and it is still used to a certain extent even at the present day. The hearth in which the operation is at present performed, differs from the forge of a common smith only in its greater size, and in the increased power of its bellows. A cavity is prepared, in which a charcoal lire is lighted, and to which the nozzle ortuyereofthe bellows is directed; ore in minute fragments is thrown upon the ignited fuel, fresh coal and ore are added from time to time, and the latter being reduced to the malleable state descends, as the charcoal burns away, to the bottom of the cavity. Here the successive portions, still kept hot by the fuel above them, agglutinate, and form a porous mass, containing in its cavities a black vitreous substance, which is composed of the earthy matter rendered fusible by the metallic oxide. This porous mass is called theLoup.
It would be unsafe to subject the loup immediately to the action of heavy hammers of iron. It is, therefore, after being withdrawn from the fire, beaten with wooden mallets, to bring its parts into closer contact, and press out the vitreous matter. While this is performed, it cools so much as to require to be again heated, which is done in the same fire. Indeed, the same forge is used in all the successive heats that the iron in this process requires.
After the loup has been again heated, it may be subjected to the hammer. This unquestionably was anciently one moved by hand; but now, in all manufactories of this character, a heavy mass of case hardened iron is employed for the purpose; this is lifted by machinery impelled by a water wheel, and permitted to fall upon the loup. The loup is again heated, and again beaten into an irregular octangular prism, called the cingle; this, after a third heat, is formed into a rectangular block, called a bloom; and the whole, or a proper proportion of this is drawn into a bar, at three successive heats; the middle being beaten out first, and the two ends in succession. Thus, in addition to the heat employed in the original reduction, the iron must be at least six times reheated before it becomes a finished marketable bar.
In this manner the ore of Elba is still manufactured in Catalonia and Tuscany, and there can be little doubt that it is identical with the original rude process, by which the iron of that most ancient of known mines was prepared to be an object of commerce. The processes in these two districts differ from each other in some minute particulars, and are known on the continent of Europe as the processesà la Catalaneandà l'Italienne. This method is known in the United States by the name ofblooming.
Bloomeries are frequent in the United States, being found in many parts of the primitive country, where the magnetic ore of iron is abundant. The iron manufactured by blooming is, generally speaking, remarkable for its nerve, being strong and tenacious in the highest degree, unless the ore be in fault. It is not, however, homogeneous, being liable to contain what are called pins, or grains that have the hardness and consistence of steel.
Blooming is comparatively an expensive process. It requires, indeed, little original capital, but the product in proportion to the capital employed is but small. It is wholly impracticable with poor ores, and demands a great length of time and expenditure of fuel, unless the ore be very fusible. Another objection to it is common to a process we shall hereafter describe, that of refining, and lies in the numerous successive heats, which the small extent of fire, and the slow process of hammering render necessary, before the bar is finished. It has been attempted in New-Jersey to lessen the expense attending these heats, by performing them in reverberatory furnaces. A saving of fuel to a small amount would probably thus be effected, but the number of heats would still remain the same. A more important and useful improvement has superseded the last; the process of rolling, which will be hereafter described, has been introduced, and by means of it a bar may be drawn out at a single heat, and at far less expense of manual labour. Such establishments exist at Dover and Rockaway, New-Jersey, which receive the iron completely reduced from the neighbouring forges, and fashion it into bars.
A forge fire, and, consequently, the process of blooming, is insufficient to convert poor ores, or those that contain much earthy matter, into iron. Treated in this way, those ores, if fusible at all, would become a mass of slag, as the earth would require, at the temperature of a forge fire, the whole, or the greater part of the metallic oxide for its fusion.
Iron being introduced, and its valuable applications known, it became necessary, in those countries that do not afford rich ores, to discover a method by which the poorer might be reduced. This could only be effected by giving such a degree of heat, as would render the earthy matter capable of melting, at a less expense of metal. To increase the mass of fuel, by increasing the depth of the cavity, and actually forming it of walls, thus enabling it to contain a greater quantity, would be obvious means of attaining this end. The ore must be added in smaller proportions, and, being longer in contact with the heated charcoal, would become carbureted; the carbon must therefore be finally burned away, before malleable iron could be attained. A rude but efficient process of this sort, is described by Gmelin as in use among the Tartars; an analogous method, whose use has been superseded by iron imported from Europe, was found among the nations of Guinea; and Mungo Park saw a more perfect application of the same principle at Camalia, on the Gambia. Furnaces of similar character, but more skilfully constructed, are still used in some parts of Germany, and are calledstuckoffen.
As a carburet, or actual cast-iron, must be formed in theseprocesses, and, as the separation of carbon at the bottom of a deep cylinder, and where the metal would probably be covered by a vitreous liquid, is difficult, the iron might sometimes resist the efforts made to render it malleable, and run from the furnace in a liquid form. It might therefore have readily occurred, that it would be less costly to finish the process in a forge. Thestuckoffenwere therefore converted intoflossoffen, or melting furnaces, whence the liquid carburet was withdrawn, and afterwards converted into bar iron. Such was probably the cause that led to the original discovery of cast iron, a discovery that cannot be traced further back than the end of the fifteenth century.
The uses of cast iron for purposes to which wrought iron is inapplicable, and the readiness withwhichit is fashioned, by pouring it into moulds, led to the increase of the size of theflossoffen, and in the power of the blowing apparatus, which has caused the introduction of the blast furnace. This forms the basis of the methods by which iron in all its forms is chiefly prepared at the present day, and is hence worthy of particular consideration.
The difference between the blast furnace proper, and the ancient fires from which it gradually took its rise, consists wholly in its superior height, and in the greater power of the blowing machines, by which its combustion is supplied with air.
This increase of height adds to the mass of the contained combustible,—additional air is therefore required for effecting its complete inflammation, and the joint effect is, that a much higher temperature is generated. By this, the earthy matters either contained in the ores, forming portions of the combustible, or added asfluxes, are rendered fusible at a less expense of oxide of iron; the carburet formed, becomes more fluid, and the product is more likely to assume the character of grey pig-iron.
Charcoal, as in the other processes, was the fuel originally employed, and is still principally used in most countries. But coal deprived of its volatile parts, and charred or converted into coke, has been substituted in some regions, as will hereafter be stated. Each of these combustibles requires a furnace of appropriate character, and demands a difference in the mode of management.
A blast-furnace is a hollow chamber enveloped, generally speaking, in a mass of masonry, of the form of a truncated pyramid. The chamber is composed essentially of three parts; the upper has the figure of a truncated cone, whose greatest base is lowest: this may be called the body of the furnace; the middle portion has also the figure of a truncated cone, whose greater base is uppermost, and is common to it and the upper portion: this contraction is called theboshesof the furnace; the lower position is called the hearth, and is usually enclosed on three sides by walls of refractory substances, on the fourth it isbounded by two stones, one serving as a lintel, which is called the tymp, the other resting on the foundation, and known by the name of thedam. Such at least is the shape of the blast furnaces in common use, and which will suffice for our present purpose.
The blast is introduced into the hearth, at a small distance above the level of the upper edge of the dam, and is now generally performed by means of twotuyeres; in the more ancient furnaces, there was but one. The furnace being completely dried, a fire is lighted in the hearth, and fuel gradually added, until the whole is filled to thetrundle head, which is the open and lesser base of the truncated cone that forms the body of the furnace. The blast may then be applied, slowly and gently at first, and increasing gradually, until it reach its maximum of intensity. As the blast proceeds, the charcoal gradually burns, and descends; its place is supplied at top by fresh fuel, by ore, and by the earthy matter used as a flux. This is styledchargingthe furnaces. The earlier charges often contain no ore, but are wholly composed of charcoal and flux, and, in all cases, the proportion of ore and flux is at first small, and is gradually augmented. The charges are made as often as the mixed mass in the furnace descends sufficiently low to admit the quantity that is chosen as the proper amount. The charcoal is thrown in first, and the ore and flux are spread and mixed upon its surface. The principles which govern the amount of the charge, are as follows:—
"The volume of the charges depends upon the capacity of the furnace. If they be too large, they cool the upper part of the furnace, which will cause great inconveniences, particularly if zinc exist in the ore. On the other hand, small charges of charcoal will be cut or displaced by the ore, which will occasion a descent by sudden falls, in an oblique direction, or in a confused manner. It follows that the volume of the charge, although proportioned to the volume of the furnace, must be augmented: when the charcoal is light and susceptible of being displaced; and with the friability, the weight, and the shape of the fragments of the ore.""The heat, considered in any given horizontal section of the furnace, will be intense in proportion to the thickness of the layer of charcoal that reaches it. It follows, that the fusible ore requires smaller charges of charcoal than one that is more refractory. If the beds of charcoal and mineral are too thick, the upper part of the furnace will not be sufficiently heated. Hence it is obvious, that there must be a maximum and minimum charge for every different dimension of furnace, and for every different species of ore and fuel."Karsten.
"The volume of the charges depends upon the capacity of the furnace. If they be too large, they cool the upper part of the furnace, which will cause great inconveniences, particularly if zinc exist in the ore. On the other hand, small charges of charcoal will be cut or displaced by the ore, which will occasion a descent by sudden falls, in an oblique direction, or in a confused manner. It follows that the volume of the charge, although proportioned to the volume of the furnace, must be augmented: when the charcoal is light and susceptible of being displaced; and with the friability, the weight, and the shape of the fragments of the ore."
"The heat, considered in any given horizontal section of the furnace, will be intense in proportion to the thickness of the layer of charcoal that reaches it. It follows, that the fusible ore requires smaller charges of charcoal than one that is more refractory. If the beds of charcoal and mineral are too thick, the upper part of the furnace will not be sufficiently heated. Hence it is obvious, that there must be a maximum and minimum charge for every different dimension of furnace, and for every different species of ore and fuel."Karsten.
The charge of charcoal being determined upon such principles, it is added by measure, and always in equal quantities, while the proportion of ore and flux is made to vary, not only by a gradual increase at the beginning of the operation, but according to the working of the furnace. The manner in which the furnace is working can be inferred, even before its products are ascertained, by the appearance of the flame at the trundle-head, and at the tymp, by the manner in which the charge descends,and more surely still, by the appearance of the scoriæ. By a strict attention to these circumstances the proportion of the charge of ore may be regulated. A fortnight usually elapses from the time of the first charge until it reaches a regular state of working, and variations will occur even after that period, in consequence of the greater or less moisture of the combustible and minerals, the continual wearing away of the sides of the furnace, the variations in the state of the atmosphere, and in the play of the blowing machines, the greater or less attention of the workmen, and numerous other accidental circumstances.
The mode of proceeding when coke is the fuel employed, rests upon the same principles, but the dimensions of furnace that are best suited to the different combustibles are different. As a general principle, the height of furnaces must depend upon the force of the blast and the density of the fuel. If the fuel be dense, and the blowing machine weak, the furnace must not have a great height; and even if the blast can be made strong, too high a furnace is disadvantageous for light charcoal. Coke, on the other hand, may be used in furnaces of greater height than any species of charcoal, provided the blast be of sufficient power. So long as the imperfect bellows were used in blowing, the height of the furnace was limited wholly by their action. More powerful apparatus in the form of cylinders, analogous in form and arrangement to those of steam-engines, and like them, either single or double acting, have now been introduced; the intensity of the blast is in them only limited by the moving power, which is applied to them, and when this is the steam engine, it may be said, that no limit can arise from the want of blast. We may, therefore, at the present day, regulate the height of furnaces by the nature of the fuel that is consumed in them.
The greater part of the furnaces in our country still retain the ancient and imperfect form of bellows, hence their height is restricted to the limits of from eighteen to twenty-four feet, and rarely or never reaches thirty. But when the apparatus is such as to supply a proper quantity of air, it has been found that even with light and porous charcoal, such as is given by white pine, the height ought not to be less than thirty feet, and when hard woods are used should be as great as thirty-six feet. Furnaces of even forty feet have been found to answer an excellent purpose, where the charcoal was prepared from oak. When coke is used, furnaces have been made as high as fifty, or even as seventy feet; but experience in England has shown, that from forty-five to forty-eight feet is the proper limit. This height is not at present exceeded in that country, even when the furnace has the greatest dimensions in other respects, and has been found efficacious, even when the vast quantity of eighteen tons has been furnished daily by a single furnace.
The force of the blast will depend upon the nature of the fuel, the volume of air, the quantity of mixed material the furnace holds; and thus furnaces in which coke is used, will require the most powerful blast, whether we have regard to the volume or the intensity. The latter may be measured by a column of mercury adapted in a syphon tube to the air pipes, exactly as the gauge is adapted to the pipes of the steam engine.
The reduction and liquefaction of the metal take place progressively, as the charges descend in the furnace. The separation of the oxygen is due to the presence of carbonaceous matter at high temperatures, begins at the surface of the pieces of ore, and proceeds gradually inwards; the earthy parts of the ore, of the fuel employed, and the flux, unite and melt; they are thus separated, and being sooner fused than the metal, make their way through the charcoal, and descend first to the hearth. The reduced metal, continuing in contact with the burning carbon, acquires a greater or less portion of that substance, becomes fusible, melts, and follows the liquified earths. Dropping into the hearth that already contains the liquid vitrified earths, it passes by its superior gravity to the bottom, and is protected by them from the blast. Even at the bottom of the hearth, the heat is sufficient to retain the carbureted metal in a liquid state, and this is permitted gradually to accumulate, until it rises nearly to the level of the dam.
It now becomes necessary to withdraw orcastthe metal. This is done by forcing a way through a channel left beneath the dam in the masonry of the hearth, and closed with clay; the inner portion of this is baked hard, and requires to be broken through with a steel point. As soon as the passage is opened, the metal runs out, and is received in a long trench formed in the sand floor of the moulding house, to which are adapted a number of less trenches, at right angles, each containing about one hundred weight of metal. The metal in the longer trench is also broken into pieces of the same size, and the ingots thus formed are calledpigs, whence the term for this variety,pig iron.
From one to three days will elapse from the time of the first charge until the furnace can be tapped, and pigs cast. From that time the casting succeeds with tolerable regularity, according to the working of the furnace, and at intervals depending upon the volume of the charge, and the capacity of the hearth.
It appears probable that the fusion of the iron is effected always by a direct chemical union of that metal with carbon, in the proportion of two atoms of the former to one of the latter. This constitutes, as we have seen, the white variety of pig iron. But as it continues, generally speaking, in the furnace, long after its fusion takes place, it acquires a temperature higher thanits proper melting point, and a tendency to separation takes place, the iron retaining in combination no more of the carbon than is necessary to maintain it in a fluid state at the increased temperature. Thus the grey variety of pig iron is formed; and on casting it, the carbon, in a form similar to that of plumbago, is disseminated throughout the mass, or forms on its surface the efflorescence that is called kish, and which is always a sign of a high quality in the iron it accompanies.
In conformity with this theory, we find that a high temperature in the furnace always produces grey cast iron; and that a low temperature, from whatever cause it may arise, renders the iron more or less inclining to white. So also if the metal be not exposed to the heat for a sufficient length of time, it becomes white.
Karsten classes these several causes of whiteness in the product, in the following order:—
"In conformity with the observations that have hitherto been made, white cast iron is obtained:"1. By the use of ores that are too easily fusible, or which is the same thing, by an excess of flux, by a want of density in the charcoal, and by too strong a blast, even when the working of the furnace is regular."2. By a surcharge of ore, which deranges the action of the furnace, and produces impure cinder, containing uncombined iron."3. By boshes of too rapid a slope, and a blast of too great a velocity; and this may occur even where the cinder is pure."4. By too low a temperature, even when the cinder is pure, and the furnace works regularly."5. By a derangement in the action of the furnace, arising not from a surcharge of ore, but from an irregularity in the descent of the charge."6. By the substances contained in the body of the furnace exercising too great a pressure upon those beneath; the heat in this case, concentrated in the hearth, cannot reach the boshes, and the upper part of the furnace; the working may be regular, the cinder and flame may in this case give no sign of derangement."7. By too great a breadth in the furnace."8. When coke is used, it may arise from too great a quantity of ashes, or of fossil charcoal, (anthracite,) being contained in it. The presence of these will keep down the heat of the furnace. An excess of ashes may be remedied, by using the ore and flux in proper proportions to fuse them, but a diminution in the charge must be made; the cinder becomes viscid, and likely to obstruct the descent of the charges."9. By an accidental cooling, arising from humidity, and other similar causes."
"In conformity with the observations that have hitherto been made, white cast iron is obtained:
"1. By the use of ores that are too easily fusible, or which is the same thing, by an excess of flux, by a want of density in the charcoal, and by too strong a blast, even when the working of the furnace is regular.
"2. By a surcharge of ore, which deranges the action of the furnace, and produces impure cinder, containing uncombined iron.
"3. By boshes of too rapid a slope, and a blast of too great a velocity; and this may occur even where the cinder is pure.
"4. By too low a temperature, even when the cinder is pure, and the furnace works regularly.
"5. By a derangement in the action of the furnace, arising not from a surcharge of ore, but from an irregularity in the descent of the charge.
"6. By the substances contained in the body of the furnace exercising too great a pressure upon those beneath; the heat in this case, concentrated in the hearth, cannot reach the boshes, and the upper part of the furnace; the working may be regular, the cinder and flame may in this case give no sign of derangement.
"7. By too great a breadth in the furnace.
"8. When coke is used, it may arise from too great a quantity of ashes, or of fossil charcoal, (anthracite,) being contained in it. The presence of these will keep down the heat of the furnace. An excess of ashes may be remedied, by using the ore and flux in proper proportions to fuse them, but a diminution in the charge must be made; the cinder becomes viscid, and likely to obstruct the descent of the charges.
"9. By an accidental cooling, arising from humidity, and other similar causes."
Among the last may be reckoned the presence of zinc in the ore. This metal, although volatile, is not separated at the temperature given in the process of roasting, nor does it sublime in the upper and cooler parts of the furnace. But, as the ore descends, it passes into the state of vapour, and requires for its conversion, great quantities of heat that becomes latent. It hence cools the lower part of the furnace far more rapidly than even wet coal, or moist ores. The cooling thus caused, may not be effected until the melted metal reach the hearth, and may therecause it to become solid. Thus the solid mass called a salamander, may, in some cases, be formed; and thus may be explained the fact, that ores of iron that contain the more easily fusible metal zinc, are more liable to interrupt the action of the furnace in this manner, than others. The volatilized zinc rises to the upper part of the furnace, where the heat is often insufficient to retain it in the state of vapour, and is then deposited on the sides. In this position, it will also disturb the action of the furnace.
Coke being more dense than charcoal, will, in its combustion, furnish a more intense heat;—hence it is hardly possible to obtain by a charcoal fire, iron of as deep a colour as may be procured by the use of the former fuel. It will also resist the pressure of far greater weights than charcoal, and hence the proportion of ore may be much greater when it is used; containing more and less fusible earthy matters than charcoal, it requires a greater quantity of flux.
In the manufacture of cast iron then, coke gives iron better suited for small castings, for those which require turning or filing, and yields a far greater quantity from a furnace. Hence arises the very great superiority which Great Britain has, until recently, possessed over most other countries, in those fabrics in which these qualities are valuable; and hence it has been found until lately, in this country, hardly possible to manufacture fine machinery that requires workmanship after it is cast, without the aid of the higher qualities of Scotch iron, which, in these qualities, exceeds even the English. Recently, however, iron fully equal to the best Scotch, but like it wanting in tenacity, has been manufactured at the Bennington furnace in Vermont:—so also at the Greenwood furnace in Orange county, N. Y., and at West Point, iron approaching to the Scotch in softness, but very superior in strength, has been produced. In these cases, the height of the furnace has been carried up to the limits we have before laid down, and powerful blowing cylinders substituted for the ancient bellows.
When the pig iron is to be used for re-casting, every effort ought to be used to obtain it of the deepest possible colour. This, as may be seen from what has been already stated, will be effected by keeping the furnace at the highest possible temperature, and exposing the metal to it a sufficient length of time. In effecting this, however, certain defects may arise:—thus a longer exposure to a high heat, will cause the reduction of other oxides that may be present, as of manganese and the metallic bases of the earths; and the iron in becoming more soft, and approaching in fact more nearly to the form of the pure metal, will combine and form alloys with these bases. In this way, it will, as has been stated, become cold short; and to this may beattributed the want of strength in the greater part, if not all, of the British iron. The use of coke as a fuel, tends to increase this defect, in consequence of the great quantity of earthy matter it contains.
When the ores are pure, cast iron manufactured by charcoal, is not liable to such a fault. Hence the cast iron of Sweden and the United States, manufactured from the magnetic iron, or, in some cases in this country, from rich hæmatites, has very superior tenacity, insomuch that these two nations have alone been able to use this material in the construction of field pieces. When white iron is obtained from a furnace, it may have two different qualities. The first arises from a mere defect of heat, where all other circumstances are favourable, and the ore is completely reduced. The second arises when the reduction is not complete, and the separation of the earths and other oxides has not been fully effected. Of all the varieties of cast iron, this latter is by far the worst. It is indeed more easily converted into wrought iron than the other species, but the product is always of very inferior quality; it is rarely or never produced by furnaces fed with charcoal, but may be obtained by accident or design in those where coke is used, by a surcharge of ore, or by too great a proportion of flux, and sometimes cannot be avoided in warm and moist weather, where the air is rarefied and charged with vapour.
The grey iron obtained by the use of each of the different kinds of fuel, has its own peculiar advantages; that made with coke possessing, as a general rule, when melted, a higher degree of fluidity which adapts it for more delicate castings; being softer and better suited for fitting; while that manufactured with charcoal, possesses a greater degree of strength. One solitary instance has been quoted, in which a manufacturer of great intelligence has obtained by the use of charcoal, from a very pure ore, a union of both these valuable properties, and another, in which iron as soft as that made with coke, has been produced by means of charcoal.
In spite of this apparent balance in the properties of the two fuels, the introduction of coke into the art of reducing iron has been attended with the most important advantages. These lie in the superior economy of the process, and in the enormous quantity of the product. The manufacture of iron by charcoal is limited, by the growth of the forests, which replace themselves only at distant periods, by the large space they occupy, and the consequent labour of transportation; by the cost of cutting the wood and preparing the coal; and finally, even when the fuel can be obtained in abundance, and at small cost, the burden of the furnace, and the heat obtained in a given space are less than when coke is used, and the quantity of metal yieldedis in consequence comparatively small. The coke furnaces of Great Britain, have therefore supplied cast iron in such abundance and at such diminished prices as to have brought it into use for a great variety of purposes, to which, until recently, it was hardly considered applicable.
In England, as in other countries, charcoal was the only fuel at first used; and after bloomeries had been in vogue for centuries, the blast furnace was introduced from the shores of the Rhine. For many years the growth of the forests proved sufficient to supply the demand, but at length the increase of population caused them to be encroached upon by cultivation; the growth of the manufacture was first prevented, and finally, almost extinguished.
The method by charcoal appears to have reached its acme of prosperity, at the close of the reign of the First James, when the furnaces of the kingdom yielded 180,000 tons of pig iron. About this period, Dudley first proposed the use of pit coal; but the time had not yet arrived in which it was absolutely necessary to seek for a new process, in consequence of the failure of the old one.
In 1745, or in the course of one hundred and thirty years, the forests had been so far encroached upon, that the product of the furnaces had fallen to 17,000 tons per annum, and in 1788, the quantity made with charcoal had dwindled as low as 13,000 tons. At this epoch, coke was introduced into blast furnaces, and in eight years the whole quantity produced by both methods had mounted up to 150,000 tons, or increased more than tenfold.
At nearly the lowest ebb of the British manufacture, the art of preparing iron was introduced into her then provinces, the present United States; and in 1737 it was attempted to obtain permission to introduce the product into England. The attempt failed, and in 1750 an act was passed to protect the exportation of English iron to America, and to prevent the establishment of forges. Had the other policy prevailed, England would probably have seen her manufacture of iron transferred to the United States, and with great immediate advantage both to herself and her then most valuable colony; but she would probably have seen herself at the present day degraded from her high stand in the scale of nations, to the secondary place in which the extent of her territory would keep her, were it not for the superiority of her manufacturing industry, of which iron is the basis. The quantity of iron now produced in England, exceeds that furnished by the rest of the world united, and does not fall short of 800,000 tons. It has a value even in its raw state of near four millions sterling, and is of far greater intrinsic worth, in consequenceof the spur which its abundance gives to every other branch of industry.
Bar iron is at the present day principally manufactured from the pig. The process originally used for this purpose is called refining. The fire in which it is performed is a forge, similar in form and character to that employed in blooming. In blooming, the iron must be reduced, combines with carbon, and is subsequently decarbureted; while in the refining, the latter part of the operation alone remains. In this last process, while the carbon is burning away, the metallic bases of the earths are then oxidated, combine with oxide of iron, and form a vitreous substance. Hence, when it is carefully conducted, by far the greater part of the impurities contained in the cast iron may be removed. Refined iron, if made from ore of equal purity, is not inferior in tenacity to bloomed, and is superior in other respects, being more homogeneous, free from pins, and more easily treated by the smith. As a general rule, it is also less costly, that is to say, the same quantity of charcoal and workmanship will furnish a greater quantity of refined iron. It requires, however, a much greater capital, and the labour of transporting the coal from the greater distances which the increased consumption of a single blast furnace and several refineries will demand, may swell the cost of that article. A bloomery fire does not require more than 2000 acres of woodland, while a blast furnace will use the charcoal of 5000. Thus it happens, that it may be more advantageous to spread a number of bloomeries over a given district of country, than to unite a blast furnace and an equal number of refineries in a single place. The celebrated iron of Sweden and Russia is refined, and our country furnishes iron prepared in the same manner not inferior in quality. The principle objection to the process is the great expense of the fuel employed, in the successive heats to which the iron must be exposed in drawing it into bars, after the processes of conversion and the separation of impurities have been effected.
As charcoal became scarce in England, it was attempted to employ coke in lieu of it, in the refineries. This, however, constantly failed, in consequence of the great intensity of the heat, by which the pig was melted suddenly instead of being exposed to the blast, long enough to burn away the carbon. Reverberatory furnaces were next tried, and with partial success, but a combined process has finally been introduced which has been successful and which is called, from a part of the operation, the method ofpuddling.
The manufacture of wrought iron, by means of bituminous coal, is executed at three successive processes, and is facilitated by very great improvements in the machinery. Where hammers are still used, they are much increased in weight, anddriven with greater velocity; but by far the greater part of the operation of drawing the bars is effected by means of rollers. The plan of these is in some measure borrowed from the slitting mill, in which bar iron is reduced into rods and thin rolls for various uses. These rollers are in sets, composed each of two of equal diameter, lying in a horizontal position, and placed one vertically above the other. Grooves corresponding to each other are cut in the two rollers, between which the heated iron is drawn by their revolution, and forced to assume a section that just fills up the two grooves. By passing in succession through grooves gradually decreasing in size, any form or magnitude may be given to the bars; and the operation is so rapid, that the bar may be drawn from the loup at a single heat.
The first operation to which the pig iron is subjected, consists in melting it in a fire called a finery, similar in form and character to the bloomeries and refineries of which we have spoken, but in which the fuel is coke. The melted metal is drawn off by tapping the furnace from beneath, and is cast into thin plates. In this way it assumes the characters of the white cast iron, which has been described as formed, when the reduction of the metal is complete, a form that cannot be given when the blast furnace in which it is made is supplied with coke. The rapidity of the cooling is increased, by throwing water on the surface of the plates. It thus appears, that this operation is adopted in order to bring the cast iron into a slate that it may often assume when manufactured by charcoal, and which cannot be given to it by coke. In conformity with this view of the subject, it has been found, that when wrought iron is manufactured by puddling, from American pig prepared by charcoal, this preliminary operation is unnecessary.
The fine metal, obtained in the manner we have described, is next broken into pieces, and subjected to heat in a reverberatory furnace. A rapid heat is given at first to liquefy the iron, and is then diminished by means of dampers; the melted mass is violently stirred to expose it to the action of air and heat, by which the carbon is burnt away, and a part of the oxides of iron and the earthy bases combined andvitrified; as the carbon is separated, the metal gradually loses its liquidity, and finally dries, or assumes the consistence of sand: this shows that the carbon is separated, and the iron has assumed its malleable nature. The addition of water aids the oxidation of the several substances, and facilitates the process. The heat is again increased, and the metal collected under it, and rolled together into parcels suited to the action of the drawing machinery, and to the size of the bar that is to be made; these are pressed together, and a partial union takes place among their particles. When they have attained a white heat, they are withdrawn in succession.In some cases, where the number of puddling furnaces is great, they are immediately carried to the rollers and drawn down. But where quality is more regarded than quantity, they are first subjected to the action of the hammer, and finally rolled. The latter process has the advantage of separating more completely the vitrefied oxides, than can be done by rolling alone, but it will often require a second heat, which is given in a forge fire called thechaffery. When rollers are used alone, a minute and half is sufficient to form the bar; and a power of thirty houses will roll two hundred tons per week.
The iron in this state is still of very inferior quality, although its external appearance may be good. It is, notwithstanding, sometimes thrown into the market, and this has given rise to the impression that prevails in this country of the bad quality of English rolled iron. It may, however, be used in some cases, where it need not be fashioned by forging; thus, where it requires no more than to be cut into lengths, or where the original bars will answer the purpose, its cheapness may recommend it. Iron for rail-roads is of this quality; and the punching of holes, by which it may be fastened down, is effected by a simple addition of steel teeth, at proper distances, to the last groove through which it is passed. In this form, ready to lay down, rail-road iron may be shipped from England at the low price of 7l.10s.sterling per ton; and a similar quality in the simple bar may probably be afforded at about 7l.We have never heard of its being sold so low as is stated in the evidence before the Committee of Congress, say 5l.5s.There was, however, a period, when an excess of production, caused by a competition between the manufacturers of Wales and Staffordshire, entailed ruin on many of them, and their articles were sold far below the price of production. The price which we have stated is lower than that which has recently been paid in England for rail-road iron, and is that of some shipped from Liverpool, 1st March, 1831, when a considerable fall had taken place.
In order to render the iron which has undergone this process merchantable, it is subjected to the third of the operations which we have enumerated. For this purpose, the bars are made from three to four inches in breadth, and half an inch in thickness. These are cut into lengths, proportioned to the weight of the bar of finished iron that is to be made, and piled together by fours, in a reverberatory furnace, similar in character to the puddling furnace. Here they are exposed to a white heat, by which the four pieces of each pile are made to adhere; they are then withdrawn, and subjected to rollers similar to those used after the puddling process, but of more careful workmanship. The cost of finishing bar iron in this way, when the pig is made by the manufacturer himself, as ascertained upon thespot by Dufrênoy and de Beaumont, is, in Wales, 8l.15s., in Staffordshire, 9l.12s.The cost of making pig iron in Wales is 4l.7s., or about half that of the finished bar iron, and in Staffordshire 5l2s.
The iron prepared by the three processes of which we have spoken, although merchantable, and suited for various common purposes, is still far from good. We give the characters by which it is distinguished, from the work of Karsten:—
"The iron prepared in the English manner, appears dense and exempt from cracks and flaws. But this goodness is only apparent; the uniform pressure to which the bars are subjected at every point, masks their defects. If a piece of this kind be taken, that in its fracture appears dense and homogeneous, and it be heated in order to be drawn out under a common forge hammer, it dilates and exhibits numerous flaws, that sometimes increase to such a degree, that the bar will fall to pieces under the hammer. It is probable that the cause of this phenomenon is due to the scoriæ, which, in this mode of working, remain mixed in the mass."
The translator adds:—
"It is not however true, that the English method of itself, injures the quality of iron,—experience has proved the contrary: it appears that soft irons lose their harshness in this operation, and become better for many uses."
It may therefore be inferred, that, when the English method is applied to pig iron, that would produce a good wrought metal by the process with charcoal, it will produce one that is equally good by means of coal, but that the latter is capable of hiding the apparent defects of even the worst iron.
The inferiority of the puddled iron is well understood in England, and therefore when it is to be used for chain cables and anchors, it is again heated, and rolled a third time, its price will be then raised to 10l.10s.Another quality still superior, is made by uniting scraps of the better qualities that we have mentioned, into loups in the puddling furnace, drawing it in the puddle rolls, balling or piling, and again rolling. Its cost will thus be raised to 12l.Even this is yet inferior to Swedes and Russia iron, which sell in the English market from 13l.to 15l.sterling per ton. For particular purposes in the fabrication of machinery, charcoal is still used in England, in manufacturing a very small quantity of iron, but of very superior quality; this, we have recently understood from good authority, is sold as high as 22l.per ton.
Thus it appears that the manufactories of England produce five different descriptions of wrought iron, four of which bear a lower price, and are therefore inferior in quality to those of Sweden and Russia, and, consequently, to the best American iron. No more than one of these, and that the lowest in quality, is usually shipped to this country, and it was the influx of this cheap and almost worthless material, which in 1816 and '17, completely prostrated the American manufacture. Under a protectingduty, it has again revived, but has not reached its former level. New capital has been invested in it under this protection, and it would be a breach of faith suddenly to withdraw it. Still sound policy would dictate that this protection should not be perpetual, provided it can be incontestably proved that it bears so hard upon other branches of industry, as to injure the country through them to a greater extent, than the benefit it derives from the manufacture of iron. But this is far from being the case. The manifest and habitual policy of our government, is to derive its revenue indirectly through the custom house, instead of seeking it in direct taxation. When these duties descend to a level with the minimum expenditure, they cannot be considered burthensome, because they in fact replace revenues that must be drawn from other sources. If, for instance, the iron employed in a specific object, appear to cost more than in some other country, that object may yet be afforded cheaper with us, in consequence of its maker being free from other burthens, which the repeal of the duty on iron, would throw upon him as a necessary substitute. If then our furnaces and forges, when a sufficient capital shall be invested in them under a protecting duty, can afford iron as cheap as it can be imported from other countries, under a minimum of duty, it cannot in truth be said, that this raw material will enhance the price of the articles manufactured from it. Let us see whether there be any reasonable prospect that we shall have iron produced in our own country, which will compete with foreign iron of equal quality, paying a duty of 25 per centum. If this be the case, the profits arising from the present protection, must, in a few years, call forth such production as will reduce the price to a proper level.
The best grey pig iron of American manufacture, superior in strength, and equal in all other respects to the Scotch, is now sold in the New York market at $45 per ton. Goodgreyiron of the usual character, is worth $35 per ton, and there is no question that forge pig could be obtained by the manufacturer of bar iron, for $25. If it were even to cost $30, it is still cheaper than Staffordshire iron, far less fit for the purpose, can be imported. The Muirkirk iron, so valuable for the casting of machinery, used to cost to import it, at the present rate of duty, $55 and $56. The Bennington furnace commenced the competition with it at this rate, but has been compelled, after driving the Scotch iron from the market, to sell at $45, which is as low as the foreign could be imported at a minimum duty.
Taking the cost of forge pig at $25, the price of converting into bars by charcoal, would be, according to the Philadelphia memorial, $18, and the ton of wrought iron ought to cost no more than $43. We however believe that this cost is far underrated, and that even by the aid of rollers in a part of the process,iron of the best quality could not be produced under $50. This is as cheap as merchantable English puddled iron can be imported, paying 25 per cent. duty. But, even if the pig cost $35, and the wrought iron, $60, it is still cheaper than the English iron, worth in that market 10l.10s.can be imported; and the latter is the cheapest which can be obtained in that country, suitable for the manufacture of anchors and chain-cables. At the present moment, however, iron cannot be produced so cheaply, for the forges and furnaces may be considered as in a great measure new, and undergoing all the difficulties of new establishments. Capital above all is wanting, from a want of confidence in the success of the enterprize, growing out of a fear of the repeal of the duty, and the recollection of the former catastrophe; and even credit, so essential where capital is deficient, is at a low ebb. Hence, if profit be made, it rather centers in the capitalist who makes the advances, than in the maker. Thus we have known iron in the bloom, sold at $45 per ton; and, when finished for the market by rolling, bring $100. The latter price, however, could not long be maintained, and has descended to $75 and $80, which still leaves the greater part of the profit to the capitalist.
But we are of opinion, that the manufacture of iron by charcoal is not that to which our country should look for its final supply. It is at best a precarious resource, and its production must diminish with the advance of agriculture, and the consequent demand, while every increase in the price of land must raise the cost. It is then to a total change in the seat and mode of manufacture, that we are to be hereafter beholden for the supply of this first necessary of civilized life. A change will first take place in the sites of the two branches; pig iron will continue to be manufactured by charcoal, and the bar converted by coal. For this the great coal field of Pennsylvania will afford the earliest facilities. No doubt can be entertained that the more freely burning varieties of anthracite will work well in the puddling furnace, as they have been successfully employed in the rolling and slitting of bar iron. When the same species of coal is mixed with charcoal in the blast furnace, it produces excellent forge pig, and thus the two species of fuel may be advantageously united, although the coal alone will not answer the purpose. The value of this coal in the mine and the cost of raising it, is as yet less than that of bituminous coal in any part of Europe, and thus we cannot avoid concluding that when it shall be brought into use, our manufacturers might compete with the English even if unprotected by duty. Our fields of bituminous coal are yet too distant from dense population, and too far removed from easy communication, to be looked to at present, but unless modes be invented by which the anthracite coal can be used without mixture in theblast furnace, these will become the ultimate seats of the manufacturing industry of the United States.
But for reducing the price of iron, by competition within our country, to a level with that of other countries, capital is required, and to divert it to this purpose, the capitalist must feel assured that he shall derive a certain profit from its investment, and that he shall be subjected to no fluctuations in price and still more in demand, from a vacillating course in the government. The establishment of works so perfect as to compete in their manipulations with the English, is a serious business, and till they be established in numbers, we must be dependent on foreign countries for no small proportion of the important article of iron that we consume. A forge for manufacturing puddled iron cannot be profitable unless its machinery be kept in regular employ, for the cost of that will be the same in all cases. This constant employment cannot be given by fewer than eighteen reverberatory furnaces, and the first cost of the works will not be less than $100,000, of which the machinery alone costs $50,000. To supply an establishment of this magnitude with pig, would employ three blast furnaces working with coke, or six with charcoal, the cost of which would reach at least $120,000. The value of the manufactured article would not fall short of a million of dollars, and would require to carry it on a floating capital of not less than $250,000. Thus it appears that a system of works for the manufacture of iron, which should compete to advantage with those of England, would find employment for a capital of half a million of dollars, even with the advantage of credit, and the ready conversion of its securities into cash through the banks. So long, then, as the policy of our government is unsettled, we can hardly expect that so vast an operation can be undertaken either by individual or by corporate funds. A division of the business has been indeed attempted; there is more than one puddling forge in the United States that relies upon the purchase of pig for its supply. These unquestionably do a fair and profitable business, but do not act to the same advantage as they would were the two branches of the manufacture united. The chief difficulty under which they labour is, that they must consult, in their location, convenience in the supply of the raw material, and must therefore neglect what would in the abstract be the most important consideration, the supply of fuel. Thus, at least one of the puddling forges of which we have spoken, is compelled to use imported fuel, and none are situated where alone the nation could derive essential benefit from them, immediately over a rich bed of coal.