IRON

IRON, on account of its abundance, working qualities, and tenacity, is probably the most useful and valuable of metals. According to Dr. Ure, "it is capable of being cast into moulds of any form, of being drawn into wire of any desired length or fineness, of being extended into plates or sheets, of being bent in every direction, of being sharpened, or hardened, or softened at pleasure. Iron accommodates itself to all our wants and desires, and even to our caprices; it is equally serviceable to the arts, the sciences, to agriculture, and war; the same ore furnishes the sword, the ploughshare, the scythe, the pruning-hook, the needle, the graver, the spring of a watch or of a carriage, the chisel, the chain, the anchor, the compass, the cannon, and the bomb. It is a medicine of much virtue, and the only metal friendly to the human frame." In its primitive position it is commingled with the earth's strata in bountiful profusion; it is found in various combinations and conditions in every formation, and it is a constituent element of both animals and vegetables.

In treating of the manufacture, properties, and production of this most important material, it will conduce to perspicuity to arrange the subject under five distinct heads, viz.—I. The History; II. The Ores and Fuel; III. The Manufacture; IV. The Strength and other Properties of Iron; V. The Statistics of the Iron trade.

Malleable iron appears to have been known from a remote antiquity. Its obvious utility and great superiority over the softer metals, then commonly used, combined with the expense of its reduction, caused it to be highly prized, though the extreme difficulty of working it by the rude methods then employed greatly restricted its application.¹ There are notices in Homer and Hesiod of the arts of reducing and forging iron, but cast-iron was then unknown, an imperfectly malleable iron being produced at once from the ores in the furnace. It is probable that the Greeks obtained most of their iron through the Phoenicians from the shores of the Black Sea, and from Laconia.

It would be interesting to trace the gradual advances which have been made in the reduction of iron from its discovery to the present time; to inquire into the circumstances which led to the successive changes in the processes, and into the principle on which those changes were founded; to examine into the differences in the products which from time to time ensued, and to notice the influence of these conditions on the extent and progress of the manufacture. Our knowledge of these changes, however, is scanty and imperfect, and we can only conjecture what was probably its early progress.

The furnaces which were first employed for smelting iron were probably similar to those now called air-bloomeries. They were probably simple conical structures, with small openings below for the admission of air, and a large one above for the escape of the products of combustion, and would be erected on high grounds in order that the wind might assist combustion. The fire being kindled, successive layers of ore and charcoal would be placed in it, and the heat regulated by opening or closing the apertures below.

The process of reduction would consist of the de-oxidation of the ore and the cementation of the metal by long continued heat. The temperature would never rise sufficiently high to fuse the ore, and the product would therefore be an imperfectly malleable iron, mixed with scoriae and unreduced oxide. It would then be brought under the hammer, and fashioned into a rude bloom, during which process it would be freed from the greater portion of the earthy impurities.

By such a process as this the Romans probably worked the iron ores of our own island; scoriae, the refuse of ancient bloomeries, occur in various localities, in some cases identified with that people by the coincident remains of altars dedicated to the god who presided over iron. Mungo Park saw a rude furnace of this kind used by the Africans, and, indeed, with some modifications, it is still retained in Spain, and along the coasts of the Mediterranean, where rich specular ores are worked.

The advantages of an artificial blast would soon become manifest, and a pair of bellows or a cylinder and piston would soon be applied to the simple construction mentioned above. Homer represents Hephaestus as throwing the materials from which the shield of Achilles was to be forged into a furnace urged by 20 pairs of bellows (πύσαι). The inhabitants of Madagascar smelt iron in much the same way, their blowing apparatus, however, consisting of hollow trunks of trees, with loosely fitting pistons.

The furnace corresponds to the blast-bloomery, and has by successive improvements developed into the blast furnace, now almost universally used, and into the Catalan forge, still employed in some districts. The application of the blast would offer considerable advantages; it would obviate the necessity of an elevated site, place the temperature more immediately under the direction of the smelter, and render the whole process more regular and certain. The method of reduction remained the same as before, but the product would differ considerably, for whenever the blast was sufficiently powerful, the iron would be fused, a partial carburation would take place, and the resulting metal would be a species of steel, utterly useless to the workmen of those days; hence, it seems necessary to infer, that a rude process of refining was invented, the metal being again heated with charcoal, and the blast directed over its surface, the carbon would be burnt out, and the iron become tough and malleable. The processes might perhaps form two successive stages of one operation, as at present practised with the Catalan forge.

The increasing demand for iron, and the progress of internal communication, would lead the smelter to increase the size and height of his bloomery, and this probably would lead to a very unexpected result. The greater length through which the ore had to descend would prolong its contact with the charcoal, and a higher state of carburation would ensue, the product being cast-iron—a compound till then perhaps unknown.

From the time that cast-iron became the product of the smelting furnace, the refining would be made a separate process, requiring a separate furnace and machinery. It would soon be found also that, as the furnace increased in height, the pressure of the superincumbent mass would render the materials so dense as to retard the ascent of the blast, and thus cause it to become soft and inefficient; hence the internal buttresses called boshes were

¹ This is shown by the epithet ωλιξυμενος (much-wrought), applied to it by Homer—Iliad, vi. 48.

The History. first introduced to support the weight of the charge, relieving the central parts from the pressure, and permitting the free ascent of the blast. Whilst the good quality of the iron and the regularity of the process were thus ensured, increase of quantity was the result of improvements in the blowing apparatus, which was now enlarged and worked by water-power. With these modifications, the furnace was the same essentially as the blast-furnace now employed, though not so large; indeed, until the introduction of coke at a much later period, the blast-furnace seldom exceeded 15 feet in height by 6 at the widest diameter. The more perfect operation of the blast furnace allowed the reduction of the heaps of scoria, which had been gradually accumulating during the period that the blast bloomeries had been in operation, and which contained 30 to 40 per cent of iron. A new species of property was thus created, extensive proprietorships of Danish and Roman cinders were formed; large deposits of scoria which for ages had lain concealed beneath forests of decayed oak, were dug up, and in Dean Forest it is computed that 20 furnaces, for a period of upwards of 300 years, were supplied chiefly with the bloomery cinders as a substitute for iron ore.

At what period the complete transformation of the blast-bloomery into the blast furnace was effected, it is impossible to say. It was probably in the early part of the 16th century, as we find that in the 17th the art of casting had arrived at a considerable degree of perfection, and in the reign of Elizabeth there was a considerable export trade of cast-iron ordnance to the Continent. In the forest of Dean are the remains of two blast-furnaces, which formerly belonged to the kings of England, but they have been out of blast since the commencement of the struggle between Charles I. and his Parliament. Calculating from the quantity of scoria accumulated in their immediate neighbourhood, which appear to have lain undisturbed for the last two centuries, Mr Mushet has attempted to deduce the period of their erection, which he conceives to have been about the year 1550, in the time of Edward VI.

Up to this period wood charcoal was the only material employed in smelting operations, but the wants of a constantly increasing population, not less than the great consumption of the blast furnaces themselves, created a scarcity of this essential material, and gave a check to the manufacture. To such an extent had the wood been destroyed, that the cutting down of timber for the use of the iron-works was prohibited by special enactments; and the forests of Sussex alone appear to have been exempt from the general decree of conservation. The number of furnaces in blast decreased three-fourths, and the annual production, which but a short time before is said to have been 180,000 tons, was in 1740 reduced to only 17,350 tons.

James I. granted patents to ironmasters in various parts of the kingdom for using pit-coal in the manufacture of iron. The obstacles to its introduction, however, were numerous, and not easily overcome. The comparatively incombustible nature of coke, and its feeble chemical affinities, rendered a more powerful blast and a longer subjection to the heat indispensable to its successful adoption. Ignorance of the causes of failure operated long and seriously, but all difficulties were at length surmounted. An enlargement of the height of the furnace prolonged the contact of the ore and coke, and at last the employment of the steam-engine and improved blowing apparatus rendered the blast much more powerful and regular, and gave that impetus to the manufacture which has caused Great Britain to take the first rank in this branch of industry.

The History. The first great improvement on the blowing apparatus was the substitution of large cylinders, with closely fitting pistons, for the bellows. The earliest of any magnitude were probably those erected by Smeaton at the Carron Iron-Works, in 1769.

In 1783-4, Mr Cort of Gosport introduced the processes of puddling and rolling, two of the most important inventions connected with the production of iron since the employment of the blast furnace. (See Addenda, A.)

About this time the steam-engine of James Watt came into use, and along with it commenced a new era in the history of the iron trade and every other branch of industry. Its immense power, economy, and convenience of application, brought it at once into general employment. It was soon applied to pumping, blowing, and rolling; it enabled the mines to be sunk to a greater depth; refractory ores to be reduced with facility, and the processes of rolling, forging, &c., to be effected with a rapidity previously unknown.

Of late years, Scotland has made considerable progress in the iron manufacture. The introduction of railway communication, and the invention of the hot-blast, have given a stimulus to the trade which has raised Glasgow into importance as an iron district, and few towns possess greater facilities for the sale of their produce, than this central depot of the mineral treasures of the country by which it is surrounded.

The hot-blast process, for which a patent was taken out by Mr Neilson in 1824, has effected an entire revolution in the iron industry of Great Britain, and forms the last era in the history of this material. This simple but effective invention has given such facilities for the reduction of refractory ores, that between three and four times the quantity of iron can be produced weekly, with an expenditure of little more than one-third the fuel; and, moreover, the coal does not require to be coked, or the ores to be calcined.

In conclusion, we may add that there appear to have been five distinct epochs in the history of the iron trade.

The first dating from the employment of an artificial blast to accelerate combustion.

The second marked by the employment of coke for reduction, about the year 1750.

The third dating from the introduction of the steam-engine, and on account of the facilities which that invention has given for raising the ores, pumping the mines, supplying the furnace with a copious and regular blast, and moving the powerful forge and rolling machinery, we may safely attribute this era to the genius of James Watt.

The fourth epoch is indicated by the introduction of the system of puddling and rolling, very soon after the employment of the steam-engine.

The fifth, and last—though not the least important epoch in the history of this manufacture—is marked by the application of the hot-blast—an invention which has increased the production of iron fourfold, and has enabled the ironmaster to smelt otherwise useless and unreducable ores; it has abolished the processes of coking and roasting, and has given facilities for a large and rapid production, far beyond the most sanguine anticipations of its inventor. Manufacturers taking advantage of so powerful an agent, have not hesitated to reduce improper materials, such as cinder-heaps and impure ores, and by unduly hastening the process, and attending to quantity more than to quality, have produced an inferior description of iron, that has brought the invention into unmerited obloquy.

II. The Ores.

The ores of iron are found in profuse abundance in every latitude, embedded in or stratified with every

The Ores. formation. They occur both crystallized, massive, and arenaceous, lying deep in strata of vast extent, filling veins and faults in other rocks, and scattered over the surface of the ground. Sometimes, but rarely, found native; usually as oxides, sulphurets, or carbonates, more or less mingled with other substances. Of these ores there are perhaps twenty varieties, many of which are, however, rare; others are combined with substances which unfit them for the manufacture of iron, so that the remainder may be classed under the following general heads: their composition, however, varies greatly:—

1. The magnetic oxides, in which the iron occurs, as $Fe\_3O\_4$ or $Fe\_2O\_3\; +\; FeO$. This is the purest ore which is worked, the best Swedish metal is manufactured from it. It is found in primitive rocks, and is widely diffused over the globe.

2. Specular iron ore, peroxide of iron, $Fe\_2O\_3$. This is rich and valuable ore, and has been worked from a remote antiquity in Elba and Spain. It is found chiefly in primary and transition rocks.

3. Red and brown haematites, hydrated peroxide of iron. These ores occur in botryoidal radiating masses, in Cumberland, Ireland, America, and other places.

4. Carbonate of iron. This ore occurs mixed with large quantities of argillaceous, carbonaceous, and silicious substances, forming the large deposits of clay-ironstone and blackbands, from which most of the iron of this country is obtained. These strata are generally found in close proximity to the coal measures.

All the above ores are more or less mixed with silica, alumina, oxide of manganese, &c., and it may not be uninteresting to glance at their geographical distribution in Europe and America.

This country possesses peculiar and remarkable advantages for the manufacture of iron. The ores are found in exhaustless abundance, usually interstratified with the coal for their reduction, and in close proximity to the mountain limestone, which is used as a flux. In few countries do these three essential materials occur in such abundance, or so near together as to give the necessary facilities for a large and profitable production.

The ores principally employed are the clay-ironstones and carbonates of blackbands, which are found interstratified with the coal fields of Ayrshire, Lanarkshire, Shropshire, South Wales, and other parts, and these vary in richness in different localities, according to position and the amount of silica clay and other foreign matter with which they are associated. The chemical composition of three varieties of the ore used in Lanarkshire is given by Dr. Colquhoun, as follows:—

The carbonic acid in the above ores may be partly combined with the lime as carbonate of lime, as well as with the peroxide of iron.

M. Berthier gives, according to Dr. Ure, the follow-

ing analyses of the English and Welsh ironstones of the The Ores. coal measures:—

Calculating the amount of carbonate of iron and metallic iron indicated by the above analyses, we have:—

The richness of the above ironstones would be about 33 per cent of iron. In the process of roasting, 28 per cent of the ore is dissipated.

Mr Mitchell gives also the following assays of clay-ironstone and blackband ore, as under:—

In North Lancashire and Cumberland, the red haematite ores are now extensively worked, and great quantities are yearly shipped from Whitehaven, Ulverstone, &c., to Staffordshire, South Wales, and Scotland, for mixing with the poorer argillaceous and blackband ores. In Cumberland and North Lancashire, no less than 546,998 tons were raised in 1854 for this purpose, and the greater portion was exported from those districts.

In addition to these exports, about 25 to 30,000 tons are smelted by the hot blast at Cleator, in the neighbourhood of Whitehaven. It produces a strong and ductile iron, considered highly valuable for mixing with the weaker irons. These ores have been carefully analysed, and contain:—

Or about 62 per cent of metallic iron.

In IRELAND there are vast deposits of iron ore of great richness, though as yet but little worked. Some of these, such as the ores worked at the Ariguan mines, and the Kidney ores of Balcarry Bay, yield as much as 70 per cent of iron. If these mines were worked more extensively, and if peat fuel were used in the smelting opera-

The Ores. tions, the iron would probably be of the very best quality, and might rival the famed Swedish charcoal metal. Of this there is now every reason to hope, as the establishment of railway communication, with almost every part of Ireland, will open out the immense peat bogs of that country, and facilitate the introduction of vegetable fuel for the reduction of the ores, and create a large and important addition to other branches of Irish industry. In a communication to the writer from Mr M'All, dated Scrabby, he states—"I have sent you samples of two kinds of iron ore, one is the red, the other the purple hæmatite. There are strata which are inexhaustible, and the ore can be raised and delivered at the furnace for less than a shilling a ton; the peat or vegetable carbon is equally cheap and abundant. Limestone of the purest quality is also close at hand, and can be delivered at the furnace at ninepence per ton. On account of the purity of these materials, iron of the greatest strength and ductility can be made, which, from its non-liability to corrode, would be admirably adapted for naval and marine purposes." Ireland is, therefore, according to Mr M'All and others, in a condition to supply large quantities of excellent iron.

The iron ores of France. France possesses an abundant supply of iron ore, but on account of the scarcity of coal, the manufacture has been greatly restricted in extent. The introduction of railway communication is, however, rapidly removing this difficulty, and the operations of smelting are greatly on the increase. The railroad has enabled the French iron-master to substitute coal for charcoal in the reduction of the iron ores, and in consequence an immense increase has taken place in the production of pig and manufactured iron. The ores are found in beds or strata in the Jura range; accumulated in kidney-shaped concretions in the fissures of the limestone; or dispersed over the surface of the ground, and but slightly covered with sand or clay.

They are found in the departments of the Yonne, the Meuse, and the Moselle, and indeed may be traced from the Pas de Calais on the north to the Jura on the south, indicating throughout an abundant and ample supply.

The present increased production of iron in France is chiefly due to the introduction of coal in smelting, but it may also be traced in some measure to the encouragement given by the Government to that branch of industry, and to the enterprise of such men as M. de Gallois and M. Dufrenoy, who have exerted themselves to extend its manufacture in that country. M. de Gallois resided in England for several years, immediately subsequent to the peace of 1815, and having obtained admission into the different iron-works here, he returned to France and established the works at St. Etienne, now probably the largest and most extensive in that country.¹ The production of crude pig-iron in France is now little short of 1,000,000 tons annually, but the demand for railways, rolling-stock, bridges, iron ships, girders, and other constructions is so great that large quantities of iron are still annually imported from this country.

The iron ores of Prussia. Valuable deposits of the blackband and clay carbonate ores are found interstratified with the great coal-field of Ruhr; and the bog-iron and hæmatite ores are found in considerable profusion in Rhenish Prussia and other parts. In Upper Silesia, on the Vistula and the Oder, large deposits of coal and iron are found in juxtaposition, and are worked to a considerable extent.

The consumption of iron is not so great as in France,

The Ores. though it is increasing rapidly, as may be seen from the returns recently given by the British Chargé d'Affairs at Berlin. These returns show that the amount of iron ore raised in Prussia has increased from 1,495,516 tons in 1853, to 2,144,509 tons in 1854; this has taken place in nearly all the producing districts, but chiefly on the Rhine, where the demand has increased from 719,684 to 1,068,656 tons; in Westphalia, from 146,320 to 330,014 tons; in Silesia, from 563,739 to 650,369 tons; in Lower Saxony and Thuringia, from 51,963 to 70,676 tons; in Prussian Brandenburg, from 8,084 to 12,731 tons; and in the Upper Zollverein from 6,736 to 12,063 tons.

In AUSTRIA, all the iron is smelted with charcoal or carbonised peat, and is in consequence of the finest quality; it may be applied to every description of manufacture, from the most ductile wire to the hardest steel. The production is, however, small. The ores are found in Hungary, Styria, Moravia, and Upper Silesia.

In BELGIUM, both coal and iron are found in equal abundance, and are worked at Charleroi, Liege, and at other places. The ores, which are chiefly hæmatite, are derived from the limestone at the base of the coal measures. (See Addenda, B.)

The superiority of the SWEDISH iron has long been acknowledged, and till recently it has been unrivalled. This arises not only from the purity of the ore—the magnetic oxide of iron—but in consequence of its being smelted with charcoal only. The quantity is, however, restricted, as the ironmasters are allowed by law only a certain number of trees per annum, in order that the forests may not be totally destroyed. Coal does not exist in either Sweden or Norway.

In 1844 some experimental researches were undertaken by Mr Fairbairn of Manchester, at the request of the Sublime Porte, in regard to the properties of iron made from the ores of Samukoff in Turkey. The ores were strongly magnetic, and contained, according to Damas and others, 62 to 64 per cent of iron. They consisted of:—

Some of these ores have been smelted with charcoal, and some very fine specimens of iron and steel produced. The manufacture is, however, in a languid state in Turkey, and although smelting furnaces, blowing apparatus, forges, rolling mills, &c., were prepared and sent out from this country, they are to a great extent useless among a people who have deeply rooted prejudices and habitual inactivity to overcome, and everything to learn in all those habits of industry which indicate the rising prosperity of an energetic and an active people.

Both the magnetic, hæmatite, and clay-ironstones abound in the United States. The magnetic ores of America worked in New England, New York, and New Jersey; the hæmatite in Pennsylvania, New York, New Jersey, and other localities; but the greater part of the manufacture must eventually establish itself in the valley of the Mississippi, west of the Alleghany range, where vast deposits of coal and iron exist, though at present but imperfectly known or developed. The ores in most of these districts are smelted with a mixture of charcoal and anthracite, and the usual limestone flux, and produce a very excellent quality of iron.

¹ The universal exhibition of last year (1855) fully justifies the remarks in reference to the great increase of the iron trade of France. Any person in the least conversant with the imperfect machinery and processes of the iron manufacture as it existed in France some years since, could not have been otherwise than struck with the improved character of those exemplified in the Paris Exhibition. In no country (probably not excepting even this) has so great progress been made in so short a time, in advancing from a state of comparative rudeness to one of considerable perfection, as in France.

In Nova Scotia some of the richest ores yet discovered occur in exhaustless abundance. The iron manufactured from them is of the very best quality, and is equal to the finest Swedish metal. The specular ore of the Acadian mines, Nova Scotia, is said by Dr. Ure to be a nearly pure peroxide of iron, containing 99 per cent of the peroxide, and about 70 per cent of iron. When smelted, 100 parts yield 75 of iron, the increase in weight being due to combined carbon. The red ore Dr. Ure states to be analogous to the kidney ore of Cumberland, and to contain:—

The Acadian ores are situated in the neighbourhood of large tracts of forests, capable of supplying almost any quantity of charcoal for the manufacture of the superior qualities of iron and steel. Several specimens of iron from these mines have been submitted to direct experiment, and the results prove its high powers of resistance to strain, ductility, and adaptation to all those processes by which the finest description of wire and steel are manufactured.

The difficulties which the Government have had to encounter, during the last two years, in obtaining a sufficiently strong metal for artillery, are likely to be removed by the use of the Acadian pig-iron. Large quantities have been purchased by the War Office, and experiments are now in progress, under the direction of Lieutenant-Colonel Wilmot, Inspector of Artillery, and of Mr. Fairbairn, which seem calculated to establish the superiority of this metal for casting every description of heavy ordnance.

There are also some very rich ores at the Nictau mines, as the following analyses by Dr. Jackson show. They contain impressions of Silurian tentaculites, spirifers, &c.—

As our limits are circumscribed, it will not be necessary to extend this section further; suffice it therefore to observe, that in all countries nature has, with a beneficent purpose, interlaid and interstratified the whole surface of the globe with this useful and indispensable material, and it would ill bespeak that high intelligence with which man is endowed if he did not avail himself of, and turn to good account, the immense stores of mineral treasures which are so profusely laid at his feet.

The enquiry into the properties and composition of the ores of iron, and the processes employed for their reduction and subsequent conversion into bars and plates, would be incomplete unless accompanied by descriptive analyses of the fuel by which they are fused. Indeed the results of the operations of smelting, puddling, &c., are

so intimately dependent on the quality of the fuel employed, as to render a knowledge of its constituents essential to the manufacture of good iron.

Charcoal was at first universally employed in the manufacture of iron, and on account of its purity compared with other kinds of fuel, and its strong chemical affinities and consequent high combustibility, it is of very superior value where it can be obtained in large quantities at a moderate cost. This, however, is rarely the case, and hence its use is restricted within very narrow limits in most countries. Charcoal is the result of several processes, in each of which the object is to increase the amount of fuel in a given bulk. The wood being cut into convenient lengths, and piled closely together, in a large heap, the interstices being filled with the smaller branches, and the whole covered with wet charcoal powder, is then set on fire. Care is taken that only sufficient air is admitted to consume the gaseous products of the wood, so as to maintain the high temperature without needlessly consuming the carbon. After the whole of the gaseous products have been separated, and the carbon and salts only are left, the access of air is prevented, and the heap allowed to cool.

Another and better process is to throw the wood into a large close oven or furnace, heated either by the combustion within it, or by a separate fire conducted in flues around it. By this process, not only is the yield greater and of better quality, from the slower progress of the operation, but the products of the distillation may be preserved and employed for a great variety of purposes. The following results of some experiments by Karsten, show the difference in yield of very rapid and very slow processes:—

These, on the average, give for the quick process 15.3, and for the slow 25.6, being in the ratio of 1 : 1.67, or 0.67 in favour of the quick process.

PEAT.—This material seems likely to come into use for smelting iron in countries such as Ireland, where neither coal nor wood are found in abundance. It is purer and less objectionable than coal, and if properly dried, compressed, and carbonized, would prove a very valuable fuel for the reduction of such ores as we have already described in the section on the iron ores of Ireland. It is carbonized in the same way as the charring of wood.

COKE.—Before the introduction of the hot-blast, this material was used to a very great extent in the manufacture of iron; it is prepared from coal in the same way that charcoal is prepared from wood, the operation being called the coking or desulphurizing process. The heaps do not require so careful a regulation of the admission of air as those of charcoal, on account of the comparatively incombustible character of the coke. Sometimes the heaps are made large, with perforated brick chimnies, to increase the draught through the mounds; at other times they are formed into smaller heaps, and the conversion takes place without the intervention of flues. The more usual and economical plan is, however, the employment of close ovens, by which process a great saving is effected, the yield being from 30 to 50 per cent in the one case,

The Fuel, and from 50 to 75 in the other, according to the nature and quality of the coal.

COAL.—The hot-blast has enabled the ironmasters to use raw coal in the blast furnaces, the great heat of the ascending current of the products of combustion coking it as it falls in the furnace. The sulphur, however, and other deleterious ingredients, do not appear to be so completely got rid of as when the coal is used in the

shape of coke; and it appears probable, that even with the hot blast, the separate process of coking might be advantageously used, on account of the greater purity of the iron produced.

The following tables, selected from various sources, give the composition of the different kinds of fuel, all of which are applicable to the reduction and fusion of the iron ores:—

According to Knapp, peat contains from 1 to 33 per cent its weight of ash. In coal we have the following from Mr Mushet's analyses:—

And again the analyses, from Overman, of the ash of coal, may be quoted, as shewing the constituents contained in the ashes derived from combustion:—

The following table of the heating power of various kinds of fuel, from Knapp's Chemical Technology, is not without interest; in practice, however, only a portion of the absolute heating power is made available:—

In concluding the observations on fuel, we may notice that the various kinds of coal are classed by mineralogists as the bituminous, and stone or anthracite coal. The first class is chiefly employed for the purpose of smelting, though, since the introduction of the hot-blast, anthracite is coming largely into use both in this country and America. Mr Crane of South Wales was the first who attempted the reduction of iron ores by anthracite, and Mr Budd, at his works at Yatalyfera, followed successfully in the same path. To these two gentlemen the public are indebted for having surmounted the obstacles to the employment of this fuel for smelting iron.

On the occasion of a visit to Mr Crane's works, nearly twenty years ago, the writer had an opportunity of inspecting some specimens of anthracite, which had passed through the furnace and been in contact with the minerals at the temperature of fusion for 48 hours, without having suffered decomposition, and were found to be charred to a depth of only three-fourths of an inch, the interior being of a perfectly shining and black colour, and quite unaffected by the heat of the furnace.

THE processes for the manufacture of iron, as we have already pointed out, are of two distinct kinds, those of cementation and those of smelting; the product of the former is imperfectly malleable iron, that of the latter, cast-iron, or iron combined with more or less carbon.

The first and older process is uncertain in its results, involves considerable expense, and as there are no efficient means of getting rid of the earthy impurities, it necessitates the employment of rich magnetic, specular, or hematite ores; on account of these defects, it is now seldom employed. The ores to be reduced by this process were heated with charcoal in open furnaces like the Catalan hearth, the fire being urged by a blast. The oxygen, water, and volatile substances were driven off, and the iron—carburized and partially fused—sunk to the bottom of the hearth. The blast was then directed downwards, so as to play over the surface of the iron, and oxidized the greater part of the combined carbon; during this operation the iron became tough and malleable, and fit for the hammer.

The annexed section (fig. 1) shows the disposition of the Catalan hearth during the process of reduction. The fuel and ore B, are piled over the hearth A, and ignited; the blast to urge the fire is applied at D, and the gaseous products of combustion pass off by the chimney C.

Mr Clay's process.

A similar process has lately been invented by Mr Clay, which appears to reduce the rich ores with great advantage, and to be free from the defects of the older process. Mr Clay mixes the ore with four-tenths of its

weight of coal, and grinds it so small that it will pass through a screen of one-eighth of an inch mesh; it is then put into the hopper A (fig. 2), from which it falls upon the preparatory bed B, at the side of the puddling furnace C. While in this position, the ore is heated, and

partly decomposed, and the coal coked. The charge is then drawn forward into the reverberatory furnace C, where it is fused by the heat of the gaseous products passing from a fire at D to the chimney F, and is puddled and balled in the ordinary way. The cinder produced contains 50 to 55 per cent of iron, is free from phosphorus, and is very suitable for smelting in the blast furnace. This process is said to produce puddled bars equal to those made by the four operations of calcining, smelting, refining, and puddling, under the old system, and appears to be peculiarly adapted for the reduction of those rich ores which cannot be smelted advantageously in the blast furnace, because the small quantity of slag which is formed does not protect the metal from the oxidizing effects of the blast.

The process of smelting in the blast furnace is now almost universally adopted for the reduction of iron ores, and for the cheapness and working qualities of the metal

The manufacture of iron produced, as well as for the rapidity of the manufacture, it is decidedly superior to all others.

Ores which contain much carbonic acid, water, or volatile matter, were at one time invariably subjected to a preparatory process of calcination, but, since the introduction of the hot-blast, they are now frequently employed in the raw state. The calcination is sometimes effected in the open air, by stacking the ore with coal, setting fire to it, and allowing it to burn out; but this method is liable to serious objection. It is impossible to keep the temperature uniform throughout the heap, and in consequence, while some portions are scarcely affected, others are fused together into large masses, which cannot be smelted without difficulty, even when broken up. Apart from the irregularity and uncertainty of the open air process, it appears to be more expensive than the calcination in kilns, when the admission of air is entirely under command. These ovens or kilns are usually built of masonry, and are placed, if possible, on a level with the charging platform of the smelting furnace. The argillaceous ores lose, during this process, 20 to 30 per cent; the carbonaceous, 30 to 40 per cent of their weight. (See Addenda, C.)

The blast furnace consists of a large mass of masonry, usually square at the base, from which the sides are carried up in a slightly slanting direction, so as to form, externally, a truncated pyramid. In the sides there are large arched recesses, in which are the openings into the furnace for the admission of the blast, and for running out the metal and cinder; at the top of the furnace is a cylindrical erection of brickwork, called the tunnel-head, for protecting the workmen from the heated gases rising from the furnace, and having one or more doors through which the charges of ore, fuel, and flux are thrown into the furnace. In front, protected by a roof, is the casting-house, where the metal is run from the furnace into moulds.

Fig. 3 is a vertical section, and fig. 4 a plan of one of the furnaces at the Dowlais Iron Works, which belong to the representatives of the late Sir J. Guest. Mr Truran, in a recently published and elaborate work on iron, has figured and described it. He states that

it is one of the largest class, 38 feet square at the base, diminishing upwards 3 inches for every vertical

foot, till it attains a height of 25 feet, where the square form ends with a moulded cap; above this, the form is circular, diminishing in diameter at a similar rate, and finishing at top with a plain moulded cornice, as a support for the charging platform. In the section and plan A is the hearth, 8 feet high and 8 feet in diameter. BB the boshes, rising to a height of 15 feet, and 18 feet wide at their greatest diameter. From the top of the boshes the body of the furnace contracts, in a barrel-shaped curve, so that at the charging platform D, at a height of 50 feet, it is only ten feet in diameter; E is the tunnel-head, with doors of iron, to admit the charges of ore and fuel; FFF the tuyere-houses, arched over and spread outwards, with the openings into the furnace for admitting the blast. G, the opening through which the iron is run from the furnace. The exterior is generally built of stone, and requires to be strongly bound with iron hoops, to prevent fracture from the expansion of the interior by the heat. The interior is lined with fire-brick set in fire-clay, a space of 2 or 3 inches being left between the two courses, to allow the expansion of the inner course. The hearth and boshes were usually constructed of refractory sandstone grit, or conglomerate, but fire-bricks are now chiefly used, and although they do not last so long, they are, in the end, more economical, and may be replaced whenever the furnace is blown out. The proper inclination of the boshes is a point of much importance, so that the materials, whilst smelting, may neither press too heavily downwards, nor yet be so retarded as to adhere in a half-liquid state to the brickwork, and cool there, thus forming what are known by the name of scaffolds, the removal of which is a source of great inconvenience.

Another form of furnace is occasionally used for the cupola smelting, called the cupola, and built much more slightly than the blast furnace. Its form is circular, and from the boshes upwards it is constructed of fire-brick, one, or sometimes two, courses in thickness. It is strongly bound together with wrought-iron hoops, and pillars of cast-iron, bolted at each end to imbedded rings of the same metal, rise through the foundation to the summit of the tuyere arches, giving considerable firmness and stability to the structure. Cheapness and facility of construction are much in its favour, and although objections have been made to the thinness of its sides, as permitting great loss of heat by radiation, it has met with very general adoption.

In addition to the cupola furnace, another of the same character has of late years been introduced. It consists

The manufacture of a truncated cone, composed entirely of boiler-plates rivetted together, as per annexed fig. 5. On the four

opposite sides recesses are cut to admit the tuyeres and the opening from the hearth into the casting-house. The interior of the furnace is lined with fire-brick and fire-clay in the usual way, and this plate furnace is not only perfectly secure, as regards the expansion and contraction, but it is found to be economical and to answer every purpose in common with the large stone and iron-bound furnaces.

Fig. 5 exhibits a plan and elevation of this description of furnace, the parts AAA being the tuyere-houses, and B for the discharge of the metal from the furnace.

The blast. The blast is usually created by a steam engine; a piston being attached to the extremity of the beam, working in a cylinder of large diameter, and forcing the air through proper valves into a large spherical reservoir, constructed of boiler-plate, whence its own elasticity causes it to flow in a regular unintermitting stream into the furnace. A cylindrical vessel, open at bottom, and immersed in a pit of water, has sometimes been used to regulate the pressure of the blast, but the water evaporated is detrimental to the working of the furnace. The nozzles by which the blast is directed into the furnace are made of cast or wrought-iron, and sometimes a current of water is conveyed round their extremities to keep them cool. The number of blow-pipe nozzles to each furnace varies at different works; the usual number is three, one for each of the tuyere houses, but sometimes six, eight, or twelve are employed; it, however, appears questionable whether this is not objectionable, as the density and penetrating power of the blast is considerably diminished by this system of diffusion. This, however, is a point which can only be decided by practice, and must be left to the

judgment of the smelter. The usual pressure of the blast as it enters the furnace is about $3\backslash frac\{1\}\{2\}$ lbs. per square inch, but in some cases it is as much as 5 lbs. per square inch. (See Addenda, D).

The communication between the ground and the tunnel-head is effected in various ways. In South Wales the furnaces are usually built on a declivity, which affords ready means of access from behind; sometimes an incline is constructed, or other contrivances, such as the balance and pneumatic lifts, are resorted to for the elevation of the materials.

The dimensions and form of the blast furnace vary greatly, according to the fashion of the district, and the notions of the builder. Yet so much does the quantity and quality of the iron depend upon the size of the furnace and strength of the blast, that we may venture to assert that the production varies in the ratio of the cubical contents of the furnace, and the volume of air admitted. Mr Truran gives the following particulars of the Dowlais Foundry iron furnace:—"The capacity is 275 cubic yards. It is blown with a blast of 5390 cubic feet of [cold] air per minute. The materials charged at the top consist of calcined argillaceous ore, coal, and limestone. The yield or consumption averages 48 cwts. of calcined ore, 50 cwts. of coal, and 17 cwts. of broken limestone, to 20 cwts. of crude iron obtained. The weekly make of iron is occasionally over 130 tons. The weekly product of cinder amounts to 250 tons. For the production of white iron for the forge, in furnaces of the same capacity as the foregoing, a larger volume of blast is employed, along with a different burden of materials. The blast averages 7370 feet per minute. The consumption of materials to one ton of iron averages 28 cwts. of calcined argillaceous ore, 10 cwts. of haematite, 10 cwts. of forge and finery cinders, 42 cwts. of coal, and 14 cwts. of limestone. With these materials the weekly produce amounts to 170 tons of crude iron, and 310 tons of cinder."

The action which takes place in the blast furnace is as follows:—The contents being raised to an intense heat by the combustion of the fuel, are brought into a softened state; the limestone parts with its carbonic acid, and combining with the earthy ingredients of the ironstone, forms, with them, a liquid slag, whilst the separated metallic particles, descending slowly through the furnace, are deoxidized and fused; in their passage they imbibe a portion of carbon, and at last settle down in the hearth, from whence they are run off into pigs about every twelve hours; the slag, being lighter, floats upon the surface of the liquid metal, and is constantly flowing out over a notch in the dam-plate, level with the top of the hearth. This slag indicates, by its appearance, the manner in which the furnace is working; thus, if the cinder is liquid, nearly transparent, or of a light greyish colour, and has a fracture like limestone, a favourable state of the furnace is indicated. Tints of blue, yellow, or green are caused by a portion of oxide of iron passing into the slag, and shew that the furnace is working cold. The worst appearance of the cinder is, however, a deep brown or black colour, the slag flowing in a broad hot rugged stream, and indicating that the supply of coke is not sufficient to deoxidize the whole of the iron.

During the process of smelting, the interior of the furnace requires to be very carefully watched. The stream of air constantly rushing in at the tuyeres, exerts a chilling agency on the melted matter directly opposed to it at its entrance. The consequence of this is the formation of rude perforated cones of indurated scoria, stretching from either side horizontally into the furnace, each one having its base directly over the embouchure of a blast-pipe. When these project only to a certain

The manufacture of iron. extent, they are favourable to the working of the furnace, as the blast is thrown right into the centre, and prevented from passing up the sides and burning the brickwork. Sometimes, however, when the furnace is driving cold and slow, these conduits of slag become so strong, and jut out so far as to meet in the middle, and thus cause a great obstruction to the entrance and ascent of the blast. When this happens, there is usually no remedy but to increase the burden, that is, to increase the quantity of moxe or ore to the charge. This causes an intense heat, the furnace is said to work hot, and the conduits of slag drop off from the sides. This, however, is followed by bad as well as good consequences; the brickwork is frequently melted, and, for a time, the iron produced is small in quantity, and of the worst quality. To bring the furnace again to its proper state, the burden must be reduced; the sides then become cool, new tubes of slag are formed, and the iron produced is good.

At the end of every twelve hours, more or less, the furnace is tapped, that is to say, the aperture in the dam-stone, which, at the commencement, had been stopped up with a mixture of loam and sand, is re-opened, and the metal contained in the hearth allowed to flow out into moulds, made in the sand of the cast-house floor, thus forming a cast or sough of pigs. When this operation ceases, the dam-stone is again secured, and the work proceeds as before. In this manner a furnace is kept continually going, night and day, and never ceases to work until repairs are necessary. Incessant action has even been thought necessary to the successful carrying on of an iron-work, but the example of perhaps the largest ironmaster in South Wales has shewn, contrary to general practice in that district, that smelting may be discontinued for at least one day in the week without any very serious derangement of operations.

Thus far we have confined our observations to the production of iron by the cold-blast process; we have now to consider the changes introduced by the employment of a heated blast.

In the year 1828, Mr J. Beaumont Neilson, a practical engineer at Glasgow, took out a patent for an "improved application of air to produce heat in fires, forges, and furnaces, where bellows or other blowing apparatus are required." Mr Neilson proposed to pass the current of air through suitably shaped vessels, where it was to be heated before it entered the furnace. In this simple substitution of a hot-blast, heated in a separate apparatus, for a cold-blast heated in the furnace itself, consists the whole invention.

Like most other improvements, the progress of this was at first slow. Retarded by practical difficulties, which beset all new processes in their first use—stopped every now and then by the prejudices of custom and ignorance, which cling with inveterate tenacity to maxims of established practice, and repel indiscriminately innovations which improve and those which modify without improving,—the invention was more than once on the point of being abandoned. A great part of the interest in its possible remuneration was transferred by the inventor to strangers, whose combined efforts and influence were necessary to insure its success. But though thus tardy in its first steps and feeble in its early efforts, the hot-blast process is now adopted at the greater number of the iron-works of Great Britain, and other parts of Europe and America.

It is perhaps not generally known that practical men, previous to Mr Neilson's invention, universally believed that the colder the blast the better was the quality and quantity of the iron produced; and this opinion appeared to be confirmed by the fact that the furnaces worked

better in winter than in summer. Acting on such views, the ironmaster actually resorted to artificial means of refrigeration, to reduce the temperature of the blast before it

entered the furnace. The fact of the improved action of the furnace in winter may perhaps be explained as a

consequence of the diminished amount of aqueous vapour contained in the atmosphere in cold weather; and the

opinion that the low temperature is the cause of the alleged increase of production has been shown to be wrong by the success of Mr Neilson's invention.

This simple invention affects only the transit of the air from the blowing cylinder to the furnace, an oven or

Fig. 9.—Plan.

stove being interposed, through which, in appropriately shaped vessels, the air is conducted, and in which it is heated to 600° or 800° Fahr., or to any other temperature adapted for the purpose of smelting.

The earliest and simplest plan by which the blast was heated is shown in the sketch, fig. 6 (p. 547). In

Fig. 11.

an oven of brickwork 0000, with a fire fed by the door D, a large cylindrical tube or receiver hh, made of rivetted boiler-plate, about 3 feet in diameter, and 8 or 10 feet long, was placed. The pipes, B and S, attached to the receiver hh at the opposite ends, communicated with the blowing-cylinder and smelting-furnace respectively. Lunular shaped partitions ppp, projecting from opposite sides on the interior of the receiver, caused the air pass-

ing through it to impinge alternately first on one side and then on the other, in order that the temperature might be uniformly and effectively communicated from the metal to the blast. By this means a moderate current of air has been heated up to 300° or 400° Fahr.

Figs. 7, 8, 9, and 10, show the apparatus first employed, Calder we believe, by Mr Dixon at Calder, and hence generally called the Calder pipes. As erected at the Butterley Iron-Works, Derbyshire, the apparatus consists of two parallel horizontal pipes LL, fig. 7, called technically the "lying pipes," one communicating with the cold-blast inlet pipe B, the other with the hot-blast outlet pipe S, fig. 9. Into sockets formed in these, the ends of the arched heating pipes hh fit tightly, as shown in fig. 7 and in fig. 10, upon a larger scale. The air, therefore, entering the inlet pipe B, figs. 8 and 9, passes over the transverse arched pipes hh, where it is exposed to the

Fig. 12.

Fig. 13.

action of a large surface of heated metal, and is delivered into the hot-blast pipe S, which conveys it at the required temperature into the blast furnace. The whole apparatus is enclosed in the oven or furnace 0000, as shown in the figs. 7, 8, and 9.

The figures of the transverse pipes vary considerably at different iron-works. Sometimes they rise up and form a large semicircular arch over the fire, 8 or 10

The manufacture of iron. feet perpendicularly, and are then connected by an arch at the top; sometimes they cross the fire in the form of a pointed arch, variously acuminated, or a single large tube is used, traversing the furnace in a long spiral direction. Their cross-section is as various as the form in which they are bent; pipes of circular, flattened

elliptical, rectangular, heart-shaped, and other sectional forms have been employed, in order to increase the heating surface in proportion to the volume of the blast. All these forms of apparatus, although admirably adapted for heating the air, are liable to fracture, from the unequal expansion of the metal.

One other form of apparatus, represented in the preceding figures, Nos. 11, 12, and 13, demands notice, on account of its great heating power. The cold air enters by the pipe M into one side of the lying pipe AA, which is divided down the centre by a partition or diaphragm, and then passes up one side of the heating pipes, which are also divided by partitions; it then turns round at the top, as shown at D (fig. 12), and descends in the direction of the arrows into the lying pipe AA on the other side to that which it entered. It is thence conveyed by the arched pipe E, fig. 13, into the second divided pipe BB, through another series of heating pipes, and ultimately escapes by the outlet pipe C, at a high temperature, to the smelting furnace. The diaphragm pipes are, however, not generally used.

The ordinary arrangement is exhibited in the drawing of one of the furnaces and heating apparatus of the Coltness Works, kindly furnished by Mr Hunter, the intelligent managing partner of that establishment. The drawings, figs. 14 and 15, represent a sectional elevation and plan of a very successful and regular working furnace, but the size and form, as already observed, require to be governed by the quality and nature of the materials that are to be used.

The more difficult the reduction of the ironstone the smaller must be the diameter of the hearth, so as to enable the blast to penetrate and circulate throughout the whole of its contents. In other conditions, where the ores are easily reduced, hearths of 9 feet diameter have been

introduced with great advantage, and that without detriment to the quality of the iron produced. The diameter of the body of the furnace is likewise regulated by the quality of the materials used, and in cases where the coal is not bituminous and the ore hard, a large diameter is found to work very irregularly; and the results have been, where furnaces have been erected 18 feet diameter, to have them reduced to only 6 feet.

The height of the furnace is also regulated by the nature of the materials and the strength of the blast by which they are reduced. Sometimes, when the coal is soft and crushes by the superincumbent pressure, it is bound or compressed to such an extent as to prevent the blast penetrating the mass, and causes an irregular working of the furnace; and, moreover, under these conditions, it makes what is called white or silvery iron.

The pressure of the blast requires also to be regulated to suit the materials, and, according to the workings at Coltness (shown in figs. 14 and 15), the pressure is about 4 lbs. on the square inch, and as much as 10,000 cubic feet of air is discharged into the furnace per minute. The temperature of the blast is 594° Fahr., and the area of the heating surface of the apparatus for raising that temperature is 3500 square feet.

The quantity of materials to make a ton of iron at these works varies in some relative proportion to their densities; but the following may be taken as a fair average of the consumption of fuel, ore, limestone, &c.:-

With the above charges the furnaces will produce from 168 to 170 tons per week, or 8,700 tons of good iron per annum.

Fig. 16 shews the general arrangement and the disposition of a hot-blast furnace, and the apparatus connected with it. J is the blowing cylinder, from which the air is forced into the receiver K, made of wrought-iron boiler plate; from this it passes by the pipe L into the heating oven, one of which is shown in section at M, and the pipe N conducts it, when heated, to the furnace. PPP are the tuyeres, FF the charging doors, E the tunnel-head.

With regard to the advantages and defects of the hot-blast process, much has been said on both sides, and the question does not appear by any means exactly settled. It is asserted, on the one hand, that iron reduced by the hot-blast loses much of its strength, whilst, on the other, it is contended that the quality of the iron is richer, more fluid, and better adapted for general purposes than that produced by the cold-blast. The advocates of the hot-blast say that the process has increased the production and diminished the consumption of coal three or four fold; and the upholders of the cold-blast maintain that the same effects may be produced, to almost the same extent, by a judicious proportion of the shape and size of the interior of the furnace, a denser blast, and greater attention on the part of the superintendent to the process.

On these points it appears to us that although the hot-blast has enabled the manufacturer to smelt inferior ores, cinder-heaps, and other improper materials, and to send into the market an inferior description of iron; this is no reason for its rejection, but rather an argument in its favour. It is true that when a strong rigid iron is required for such works as bridges or artillery, the somewhat uncertain character of hot-blast metal renders it objectionable, but this appears to be due rather to the carelessness or want of attention in the manufacture than to the use of heated air or defects in the process. On the other hand, the hot-blast, by maintaining a higher temperature in the furnace, ensures more effectually the combination of the carbon with the iron, and produces a fluid metal of good working qualities, generally superior to cold-blast iron, in cases where great strength is not required; and, moreover, we have yet to learn why even the strongest and most rigid iron cannot be made by this process. The comparative strength of hot and cold blast iron will, however, be given in another part of this article; for the present it is sufficient to observe that the results of the experiments are not unfavourable to the hot-blast

In 1830, the weekly produce of three furnaces, coke, and air at $300^\{\backslash circ\}$ Fahr. being used, was 162 tons 2 cwt.; and the average of coal to one ton of iron was reduced to 5 tons 3 cwt. 1 qr. In 1833, the weekly produce of four furnaces, raw coal, and air heated to $600^\{\backslash circ\}$ being used, was 245 tons; and the average of coal to one ton of iron was reduced to 2 tons, 5 cwt. 1 qr.

"On the whole then, the application of the hot-blast has caused the same fuel to reduce three times as much iron as before, and the same blast twice as much."

This decrease in the amount of fuel and blast required for the reduction of iron, Dr. Clark accounts for by shewing, that in an ordinary furnace, "2 cwt. of air a minute or 6 tons an hour are injected into the furnace." This he considers "a tremendous refrigeratory passing through the hottest part of the furnace," and to a great extent repressing the temperature which is necessary for the complete and rapid reduction of the iron.

Mr Truran considers that "writers on the hot-blast have greatly exaggerated the effects of this invention on the iron manufacture of this country. If we are to believe the majority of them, the great reductions which have been effected within the last 25 years, in the quantities of fuel and flux to smelt a given weight of iron, and the large increase of make from the furnaces, is entirely owing to the use of this invention. That the hot-blast, under certain circumstances, has effected a saving in the consumption of fuel, and also augmented the weekly make, we freely admit. But the saving of fuel, and increase of make due to its employment, is not generally one-fourth of the quantity which writers have asserted." Here Mr Truran is at issue with Dr Clark, and denies the cooling effect of a cold-blast. He attributes the effects of a heated-blast, "first, to the caloric thrown into the furnace along with the blast, enabling a corresponding quantity of coal to be withdrawn from the burden of materials, with a proportionate reduction in the volume of blast, the effects of which are seen in an augmentation of the make, but do not result in any saving of fuel; secondly, to the reduced volume of blast and large proportion of caloric which it carries into the furnace, causing a diminished consumption of fuel in the upper parts of the furnace." Although we do not agree with all Mr Truran's strictures on the hot-blast, the consumption of fuel in the throat is, nevertheless, a question well worthy of investigation. The combustion

iron, either as regards its resistance to a transverse strain, or its power to resist impact.

Dr. Clark, Professor of Chemistry in the University of Aberdeen, investigated the merits of the hot and cold-blast process in regard to the consumption of fuel, as early as 1854-5. He states, that after the hot-blast had been brought fully into operation at the Clyde Iron-Works, "during the first six months of the year 1833, one ton of cast-iron was made by means of 2 tons 5 1/4 cwt. of coal, which had not previously to be converted into coke; adding to this 8 cwt. of coal for heating, we have 2 tons 13 1/4 cwt. of coal required to make one ton of iron. In 1829, when the cold-blast was in operation, 8 tons 1 1/4 cwt. of coal had to be used. This being almost exactly three times as much, we have from the change of the cold-blast to the hot, combined with the use of coal instead of coke, three times as much now made from the same quantity of coal." Dr. Clark adds the following statistics of the Clyde Iron-Works:—

In 1829, the weekly produce of three furnaces, cold air and coke being used, was 110 tons 14 cwt.; and the average of coal to one ton of iron was 8 tons 1 cwt. 1 qr.

The manufacture of iron is of course largely increased by the narrow form of throat given to furnaces, which greatly increases the effect of the blast there, and accounts for the difficulty of using those kinds of coal, in the raw state, which splinter if rapidly heated. If Mr Truran's conjectures be correct, and it be found, that by increasing the area of the throat, raw coal and anthracite can be advantageously used with a cold-blast, the superiority of the hot-blast will not be so decidedly marked. This must, however, be determined by practice; as at present, certainly, it is well known that the anthracite and splint coal can be used most effectively and economically with the hot-blast.

We quote from one more authority on this subject. M. Dufrenoy, in his report to the Director-General of Mines in France, states, that upon heating the air proceeding from the blowing cylinder up to 612° Fahr., a considerable saving in fuel was effected by the use of raw coal instead of coke, and that this caused no derangement of the working of the furnace or deterioration of the iron produced. On the contrary, "the quality of the metal was improved, and a furnace which, when charged with coke, produced only about half No. 1 and half No. 2 pig-iron, gave a much larger proportion of No. 1 after the substitution of raw coal. Besides this, the quantity of limestone was considerably diminished." This last circumstance, according to M. Dufrenoy, is due to the increased temperature of the furnace, which fuses more readily the earthy matter and other impurities in combination with the ores.

To show the saving effected, M. Dufrenoy gives the quantities used in each of the experiments at the Clyde Iron-Works:—

In 1829, the combustion being produced by cold air, the consumption for one ton of iron was—

In 1831, the furnaces being blown with air heated to 450° Fahr.—

In July 1833, the temperature of the blast being raised to 612° Fahr., and the fusion effected by raw coal, the consumption per ton of iron was—

Since that time, the employment of a blast heated to 800° or 900° has still further increased the weekly production and saving of fuel.

Collection of the waste gases.

The Waste Gases.—From the description that we have given of the smelting operations, it is evident that a large volume of gaseous products are constantly escaping at the top of the blast-furnace. These are found to contain a large proportion of unconsumed inflammable gas, capable of developing heat, and in countries where fuel is expensive, it is of great importance that these should be applied to useful purposes, and not be wasted in the atmosphere. Various contrivances have been adopted for this purpose, and in some places, particularly on the Continent, they have been utilized with great economy.

To enable the waste gases to be collected and applied to raising steam, heating hot-blast stoves, &c., without detriment to the working of the blast-furnace, it is necessary to withdraw them at an elevation where they have completed their work, yet at such a distance from the mouth of the furnace that they may be extracted in a dry state, and before they come into contact with the atmosphere, so as to cause combustion. This may be effected, either by increasing the height of the blast-furnace, withdrawing a portion of the gases through

apertures in the side, or, if the furnace be not too large, by closing the top of the furnace with a moveable door. Fig. 17 shows the first plan; AA are the apertures through which the gases escape by the chamber BB into the pipe C, which conveys them to the place where they are burnt. The requisite pressure for causing the gases to escape at AA is obtained by heaping the charges of fuel and ore to some height above them. Fig. 18 shows

another contrivance for the same purpose; a casting AA in the shape of a truncated cone is fixed at the top of the furnace, the small diameter downwards; the aperture in the bottom of this is closed by another conical casting B, supported by a chain and counterpoise weight; this evidently shuts the mouth of the furnace, and the gases pass off by the pipe C. When a charge is to be thrown in, it is emptied into the cone hopper AA. When the charge is complete, the moveable cone B is lowered so as to enable the charge to pass between it and the edges of the hopper when it is again raised, and the operations of the furnace proceed as before.

In this country sufficient attention has not been paid to this economical practice, as compared with what has been done in other countries where fuel is expensive. It is no excuse that fuel is cheap, as in most cases the gases can be applied with economy, and their combustion tends to abate the serious nuisance of smoke.

The Conversion of Crude into Malleable Iron.

The conversion of the carburised crude iron, obtained from the blast furnace, into malleable or wrought iron is

The manufacture of iron, effected by several operations of an oxidising character, in which it is sought to separate, in the gaseous state, the carbon contained in the iron, by combining it with oxygen, whilst the other metals alloyed with the iron and the phosphorus pass into the slag.¹

Methods of conversion with charcoal and coke iron. In reference to subsequent operations, the iron produced in the smelting furnace may be divided into two kinds—that reduced by charcoal and that reduced by coke or raw coal. When charcoal iron has to be converted by charcoal, as in Sweden, it is decarburised in the charcoal refinery, with or without an intervening process. Where coal can be obtained, however, it is now usually converted by the process of puddling. Pig iron produced by coke or coal is converted into malleable iron either by decarburisation in the refinery or oxidising hearth, and subsequent puddling, or it is converted at once in the puddling furnace by the process of boiling, which is equally effective, and is now more generally practised.

Messrs Rushton & Eckersley's works. This last process, as the one most generally adopted in this country, deserves a special notice, and we are fortunate in having before us the particulars of the manner in which it is conducted by Messrs Rushton and Eckersley of Bolton, kindly furnished by Mr Rushton, the senior partner of the firm. This establishment is probably one of the most modern and complete of the kind in the kingdom; it is one that has spared no expense in the application of useful inventions, and has kept pace with every improvement that has taken place in the manufacture of bar and plate iron for the last fifteen years.

The machinery and appliances at these works consist of:—

• 6 Steam engines, of 180 total nominal HP.
• 2 Five-ton and 2 fifty-cwt. steam hammers.
• 3 Helve hammers.
• 1 Set of puddled iron rolls.
• 1 Set of boiler plate rolls.
• 1 Merchant train and balling mill.
• 16 Puddling furnaces.
• 14 Balling and scrap furnaces.

And other machinery, such as plate and bar shears, lathes, &c.

Mixing of hematite ore with iron to be converted. At Messrs Rushton and Eckersley's works, a small proportion of the Cumberland haematite ore is mixed with the crude pig iron to be converted, as it is found to assist in the process of boiling in the puddling furnace, and in other respects to facilitate the process and improve the quality of the iron.

Classification of various kinds of iron. The crude pig iron is assorted according to the degree and uniformity of its carburisation, and classed as Nos. 1, 2, 3, &c.; No. 1 being most highly carburised, No. 2 less so, and so on to No. 4, which contains much more oxygen than the others. The carbon combined with iron gives it fusibility and fluidity, but deprives it of ductility. To render it malleable and capable of being welded, it must be deprived as far as possible of all the extraneous substances which have been mixed with it in the blast furnace, more especially of the carbon. Prima facie, therefore, it would appear that the highly carburised pig iron is the most suitable for casting, whilst that containing least carbon is best adapted for conversion into malleable iron; hence, in the trade, the crude iron is divided into foundry and forge pigs.

Difficulties in the way of converting highly carburised iron. The pigs, however, in which carbon most predominates, and which, as a rule, have been most effectually separated from all other impurities during the process of smelting, are in many respects preferable for the manufacture of wrought iron; up to this time, however, great practical difficulties have attended the decarburisation of

iron containing so much carbon, and the white or forge iron is almost always preferred, measures having been taken for depriving it of the metals and earthy impurities not separated in the blast furnace.

With regard to the process of refining, we may observe, that the crude iron is melted in a hollow fire, and partially decarburised by the action of a blast of air forced over its surface by a fan or blowing engine. The carbon having a greater affinity for the oxygen than for the iron, combines with it, and passes off as gaseous carbonic oxide or carbonic acid. During this process, a portion of the silicon, &c., is fused out, and separated from the iron. It is obvious from the above that the iron to be refined, being placed in contact with fuel at a high temperature, is liable to be deteriorated by the admixture of sulphur and other impurities of the fuel; and as the iron is only partially exposed to the action of the blast, the operation is necessarily, under these circumstances, imperfect. From the refinery the metal is run out into large moulds, and is then broken up into what is technically distinguished as "plate metal."

The process of puddling succeeds that of refining; and in this operation the reverberatory furnace is employed, with the fire separated by a partition or bridge from the hearth, on which is placed the metal to be puddled. By this arrangement the flame is conducted over the surface of the metal, creating an intense heat, though the deleterious portions of the fuel cannot mix with the iron. In this furnace the iron is kept in a state of fusion, whilst the workman, called the "puddler," by means of a rake or rubble, agitates the metal so as to expose, as far as he is able, the whole of the charge to the action of the oxygen passing over it from the fire. By this means the carbon is oxidised, and the metal is gradually reduced to a tough, pasty condition, and subsequently to a granular form, somewhat resembling heaps of boiled rice with the grains greatly enlarged. In this condition of the furnace the cinder or earthy impurities yield to the intense heat, and flow off from the mass over the bottom in a highly fluid state.

The iron at this stage is comparatively pure, and quickly becomes capable of agglutination; the puddler then collects the metallic granules or particles with his rubble, and rolls them together, backwards and forwards, over the furnace bottom, into balls of convenient dimensions (about the size of thirteen-inch shells), when he removes them from the furnace to be subjected to the action of the hammer or mechanical pressure necessary to give to the iron homogeneity and fibre. These processes of refining and puddling have universally been employed till recently; but improvements have rendered it simpler, and the refining process is now very generally abolished.

Shortly after the employment of the puddling process, it was found advantageous to mix a portion of crude iron with the refined plate metal, the expense of the process of refining being saved upon the iron used in the crude state; and trusting to the decarburising effects of the puddling furnace, it was found that the refining process might be altogether dispensed with, if the crude iron containing a proportion of oxygen and very little carbon was employed. In this single process it is to be observed, that as all the carbon has to be got rid of in the puddling furnace, the evolution of gas is much more violent, the fluid iron boiling and bubbling energetically during the period of its disengagement, and hence the operation has acquired the popular name of the "boiling" process.

¹ See Mr. Blackwell's paper, On the Iron Industry of Great Britain, read before the Society of Arts.

In this operation the pig iron when melted is more fluid, on account of containing a greater proportion of carbon than the metal from the refinery, and requires more labour in stirring it about and submitting it to the action of the current of air; the process, moreover, is attended by a greater waste of iron than puddling either plate, or crude iron and plate mixed, but not so great a loss as in the two operations of refining and puddling. It must, however, be admitted that the superior fluidity of the iron in the boiling process has a more injurious action on the furnace. Notwithstanding these objections, the system of boiling without the intermediate process of refining has been gaining ground for the last ten years, and in many places has entirely superseded the use of the refinery; recent events have therefore led to the conclusion, that in a short time the refining process will have become a thing of the past.

Numerous attempts have been made to secure a more scientific and perfect decarburisation of the crude iron, but without success. One improvement, however, recently patented by Mr. James Nasmyth, gives promise of making the boiling process as nearly perfect as we may hope to see it. It has been in use for two years at the Bolton Iron Works, and from its constant employment in the puddling furnaces of that establishment, it has given direct proof of its utility, and is gradually extending itself among the large manufacturers as its advantages become known.

The invention consists of the introduction of a small quantity of steam at about 5 lbs. pressure per square inch, into the molten metal as soon as it is fused, as the oxygen of the steam has at that high temperature a greater affinity for carbon than for the hydrogen with which it is combined or for the iron, the carbon is rapidly oxidised off. The liberated hydrogen has no affinity for the iron, but unites with sulphur, phosphorus, arsenic, &c.—substances very injurious to the quality of the iron, if present even in minute quantities, and yet frequently found in the ores and fuel.

The mode of operating is as follows:—The steam is conveyed from the boiler to a vertical pipe fixed near the furnace door, having at its lower end a small tap or syphon, to let off the condensed steam, and prevent its being blown into the furnace. A cock with several jointed pieces of pipe are fastened to the flange of the vertical pipe, so as to form, as it were, jointed bracket pipes, somewhat similar to those of gas pipes, which

the tap or steam cock, cc the elbow-jointed tubes, CC the handle, and DD the steam tube or rabble, bent at the end, so as to inject the steam on the liquid metal GG. This apparatus is introduced into the furnace immediately the iron is melted, the puddler moving it slowly about in the molten iron, while the steam pours upon it through the bent end of the tube. In the course of from five to eight minutes the mass begins to thicken, the steam pipe is withdrawn, and the operation finished in the ordinary way with the common iron rabble. The time saved by this process in every operation or heat, as it is technically called, averages from ten to fifteen minutes, and that during the hottest and most laborious part of the operation.

By means of this apparatus, the highly carburized pig iron, which is the most free from impurities, is rendered malleable in one furnace operation, without the deteriorating adjuncts of the refining and puddling process as ordinarily practised; in this operation no deleterious substance can combine with the iron, whilst in the refinery process the mixture of the fuel and metal is liable to deteriorate the latter with sulphur, silicon, &c. This new process, it is affirmed, has a beneficial effect in purifying the iron with greater economy and rapidity than any other process with which we are acquainted.

Irrespective of the improvements just described, there is another which is extensively used on the Continent, denominated the Silesian gas furnace. For a drawing and explanation of this furnace we are indebted to Mr. Anderson, inspector of machinery at the arsenal, Woolwich. The following drawing, fig. 20, will explain the new Silesian furnaces which are used in the manufacture of iron in that country, in place of our reverberatory air furnaces, and are said, on good authority, to be a very great improvement, not only in regard to the entire prevention of smoke and the economy of fuel, but also in simplifying the wrought-iron manufacture, and enabling a less skilled class of workmen to manage the furnaces.

The chief feature is the gas generator, which may be described as a close brick chamber with an opening at the bottom for the admission of air from a fan, by means of which the gases are driven out of the chamber into the furnace amongst the iron to be heated. At the point where the gases enter the furnace, a series of tuyeres are provided for the admission of air from the same fan. The pipes that convey the air and the gas from the retort to the tuyeres are both provided with valves, in order that the attendant may modify the quantity from either source, so as to produce any intensity of flame the work may require, and also to produce perfect combustion, thus placing the entire action of the furnace under complete control. It is about eleven years since these furnaces were first introduced, and notwithstanding the prejudices that were naturally raised against them, they are said to be now extensively adopted in the Silesian district, and in great favour with both the master and the workmen.

In this description of furnace there appear to be three great advantages over the air furnace—

1st, The entire absence of smoke, in consequence of complete combustion.

2d, The saving of upwards of 33 per cent in fuel, from the whole of the gaseous products being made available, and there being no necessity for the flame to pass up the chimney to produce draught, as in the case of the reverberatory furnace, which requires an inordinate supply of fuel as compared with what is wanted to work the fan.

3d, The absolute control the attendant has over the

Fig. 19.

allow free motion in every direction, as in the annexed sketch, in which A, fig. 19, is the reverberatory furnace, a the vertical steam pipe communicating with the boiler,

The manufacture of iron, as regards the temperature and the simplicity with which it can be worked. Its operations in this respect are, according to those who have seen it at work, so perfect as to be as precise in its action as a machine.

From this description it would appear that the iron-masters of this country have not made themselves acquainted with these improvements, but having some knowledge of the efficiency and existence of this process,

we would earnestly recommend it to their attention, as an invention in more respects than one entitled to consideration.

On this new field of inquiry, he set out with the assumption that crude iron contains about 5 per cent. of carbon; that carbon cannot exist at a white heat in the presence of oxygen without uniting therewith, and producing combustion; that such combustion would proceed with a rapidity dependent on the amount of surface of carbon exposed; and, lastly, that the temperature which the metal would acquire would be also dependent on the rapidity with which the oxygen and carbon were made to combine, and consequently, that it was only necessary to bring the oxygen and carbon together in such a manner that a vast surface should be exposed to their mutual action, in order to produce a temperature hitherto unattainable in our largest furnaces. With a view of testing practically this theory, he constructed a cylindrical vessel of three feet in diameter, and five feet in height, somewhat like an ordinary cupola furnace, the interior of which was lined with fire-bricks, and at about two inches from the bottom of it he inserted five tuyere pipes, the nozzles of which were formed of well-burnt fire clay, the orifice of each tuyere being about three-eighths of an inch in diameter; they were put into the brick lining from the outside, so as to admit of their removal and renewal in a few minutes, when they were worn out. At one side of the vessel, about half way up from the bottom, there was a hole made for running in the crude metal, and in the opposite side was a taphole, stopped with leam, by means of which the iron was run out at the end of the process. In practice, this converting vessel may be made of any convenient size, but he prefers that it should not hold less than one or more than five tons of fluid iron at each charge. The vessel should be placed so near to the blast furnace as to allow the iron to flow along a gutter into it; a small blast cylinder is required, capable of compressing air to about 8 lbs. or 10 lbs. per square inch. A communication having been made between it and the tuyeres before mentioned, the converting vessel will be in a condition to commence work; it will, however, on the occasion of its first being used, after relining with fire-bricks, be necessary to make a fire in the interior with a few baskets of coke, so as to dry the brickwork

Since the above was written, an apparently new light has been thrown on the conversion of iron, by a paper read by Mr H. Bessemer at the last meeting of the British Association for the advancement of science, held at Cheltenham in August last (1856). In this paper the author announces to the world the discovery of an entirely new system of operations for the manufacture of malleable iron and steel. The crude metal is converted, by one simple process, directly as it comes from the blast furnace. We should detract from its clearness did we attempt to curtail the lucid description in which Mr Bessemer has recommended his invention to the manufacturers and the public; we therefore give the account in his own words:—

Mr Bessemer states that "for the last two years his attention has been almost exclusively directed to the manufacture of malleable iron and steel, in which, however, he had made but little progress until within the last eight or nine months. The constant pulling down and rebuilding of furnaces, and the toil of daily experiments with large charges of iron, had begun to exhaust his patience, but the numerous observations he had made during this very unpromising period, all tended to confirm an entirely new view of the subject, which at that time forced itself upon his attention, viz.—that he could produce a much more intense heat, without any furnace or fuel, than could be obtained by either of the modifications he had used, and consequently, that he should not only avoid the injurious action of mineral fuel on the iron under operation, but that he would, at the same time, avoid also the expense of the fuel. Some preliminary trials were made on from 10 lbs. to 20 lbs. of iron, and although the process was fraught with considerable difficulty, it exhibited such unmistakable signs of success, as to induce him at once to put up an apparatus capable of converting about 7 cwt. of crude pig iron into malleable iron in thirty minutes. With such masses of metal to operate on, the difficulties which beset the small labo-

and heat up the vessel for the first operation, after which the fire is to be carefully raked out at the tapping hole, which is again to be made good with loam. The vessel will then be in readiness to commence work, and may be so continued until the brick lining, in the course of time, is worn away, and a new lining is required. The tuyeres, as before stated, were situated nearly close to the bottom of the vessel, the fluid metal therefore rose some eighteen inches or two feet above them. It was therefore necessary, in order to prevent the metal from entering the tuyere holes, to turn on the blast before allowing the fluid crude iron to run into the vessel from the blast furnace. This having been done, and the fluid iron run in, a rapid boiling up of the metal was heard going on within the vessel, the iron being tossed violently about, and dashed from side to side, shaking the vessel by the force with which it moved. Flame, accompanied by a few bright sparks, immediately issued from the throat of the converting vessel. This state of things lasted for about fifteen or twenty minutes, during which time the oxygen in the atmospheric air combined with the carbon contained in the iron, producing carbonic acid gas, and at the same time evolving a powerful heat. Now as this heat is generated in the interior of, and is diffusive in innumerable fiery bubbles throughout the whole fluid mass, the vessel absorbs the greater part of it, and its temperature becomes immensely increased, and by the expiration of the fifteen or twenty minutes before named, that part of the carbon which appears mechanically mixed and diffused through the crude iron has been entirely consumed. The temperature, however, is so high that the chemically combined carbon now begins to separate from the metal, as is at once indicated by an immense increase in the volume of flame rushing out of the throat of the vessel. The metal in the vessel now rises several inches above its natural level, and a light frothy slag makes its appearance, and is thrown out in large foam-like masses. This violent eruption of cinder generally lasts about five or six minutes, when all further appearance of it ceases, a steady and powerful flame replacing the shower of sparks and cinders which always accompanies the boil. The rapid union of carbon and oxygen which thus takes place, adds still further to the temperature of the metal, while the diminished quantity of carbon present allows a part of the oxygen to combine with the iron which undergoes a combustion, and is converted into an oxide. At the excessive temperature that the metal has now acquired, the oxide, as soon as formed, undergoes fusion, and forms a powerful solvent of those earthy bases that are associated with the iron. The violent ebullition which is going on mixes most intimately the scoria and metal, every part of which is thus brought into contact with the fluid oxide, which will thus wash and cleanse the metal most thoroughly from the silica and other earthy bases, which are combined with the crude iron, while the sulphur and other volatile matters, which cling so tenaciously to iron at ordinary temperatures, are driven off, the sulphur combining with the oxygen, and forms sulphurous acid gas. The loss in weight of crude iron during its conversion into an ingot of malleable iron, was found, on a mean of four experiments, to be 12½ per cent, to which will have to be added the loss of metal in the finishing rolls. This will make the entire loss probably not less than 18 per cent instead of about 28 per cent which is the loss on the present system. A large portion of this metal is, however, recoverable by treating with carbonaceous gases the rich oxides thrown out of the furnace during the boil. These slags are found to contain innumerable small grains of metallic iron, which are mechanically held in suspension in the slags, and may be

easily recovered. It has already been stated that after the mass-
the boil has taken place, a steady and powerful flame ^{facture of}
succeeds, which continues without any change for about ^iron.
ten minutes, when it rapidly falls off. As soon as this
diminution of flame is apparent, the workman knows that
the process is completed, and that the crude iron has
been converted into pure malleable iron, which he will
form into ingots of any suitable size and shape, by simply
opening the tap hole of the converting vessel, and allow-
ing the fluid malleable iron to flow into the iron ingot
moulds placed there to receive it. The masses of iron
thus formed will be perfectly free from any admixture of
cinder oxide, or other extraneous matters, and will be
far more pure, and in a forwarder state of manufacture,
than a pile formed of ordinary puddle bars. And thus,
by a single process, requiring no manipulation or parti-
cular skill; and with only one workman, from three to
five tons of crude iron passes into the condition of several
piles of malleable iron, in from thirty to thirty-five min-
utes, with the expenditure of about one-third part the
blast now used in a finery furnace with an equal charge
of iron, and with the consumption of no other fuel than
is contained in the crude iron. To those who are best
acquainted with the nature of fluid iron, it may be a
matter of surprise that a blast of cold air forced into
melted crude iron is capable of raising its temperature
to such a degree as to retain it in a perfect state of fluid-
ity, after it has lost all its carbon, and is in the condi-
tion of malleable iron, which, in the highest heat of our
forges, only becomes a pasty mass. But such is the
excessive temperature that may be arrived at, with a
properly shaped converting vessel, and a judicious distri-
bution of the blast, that not only may the fluidity of the
metal be retained, but so much surplus heat can be
created as to remelt the crop ends, ingot, runners, and
other scrap, that is made throughout the process, and
thus bring them, without labour or fuel, into ingots of a
quality equal to the rest of the charge of new metal.
For this purpose, a small arched chamber is formed
immediately over the throat of the converting vessel,
somewhat like the tunnel-head of the blast furnace.
This chamber has two or more openings in the sides of
it, and its floor is made to slope downwards to the throat.
As soon as a charge of fluid malleable iron has been
drawn off from the converting vessel, the workman will
take the scrap intended to be worked into the next
charge, and proceed to introduce the several pieces into
the small chamber, piling them up round the opening of
the throat. When this is done, he will run in his charge
of crude metal, and again commence the process. By
the time the boil commences, the bar ends or other scrap
will have acquired a white heat, and by the time it is
over, most of them will have melted and run down into
the charge. Any pieces, however, that remain, may then
be pushed in by the workman, and by the time the pro-
cess is completed, they will all be melted and intimately
combined with the rest of the charge; so that all scrap
iron, whether cast or malleable, may thus be used up
without any loss or expense. As an example of the
power that iron has of generating heat in this process,
Mr Bessemer mentions that when trying how small a set
of tuyeres could be used, the size he had chosen proved
too small, and after blowing into the metal for one hour
and three-quarters, he could not get up heat enough with
them to bring on the boil. The experiment was there-
fore discontinued, during which time two-thirds of the
metal solidified, and the rest was run off. A larger
set of tuyere pipes were then put in, and a fresh charge
of fluid iron run into the vessel, which had the effect
of entirely remelting the former charge; and when

The manufacture of iron. the whole was tapped out it exhibited, as usual, that intense and dazzling brightness peculiar to the electric light.

"To persons conversant with the manufacture of iron, it will be at once apparent that the ingots of malleable metal which are produced by this process, will have no hard or steely parts, such as are found in puddled iron, requiring a great amount of rolling to blend them with the general mass, nor will such ingots require an excess of rolling to expel the cinder from the interior of the mass, since none can exist in the ingot, which is pure and perfectly homogeneous throughout, and hence requires only as much rolling as is necessary for the development of fibre; it therefore follows that instead of forming a merchant bar or rail by the union of a number of separate pieces welded together, it will be far more simple, and less expensive, to make several bars or rails from a single ingot; doubtless this would have been done long ago had not the whole process been limited by the size of the ball which the puddler could make.

"The facility which the new process affords, of making large masses, will enable the manufacturer to produce bars that, on the old mode of working, it was impossible to obtain; while, at the same time, it admits of the use of some powerful machinery, whereby a great deal of labour will be saved, and the process be greatly expedited. Mr Bessemer merely mentions this in passing, without entering into details, as the patents he has obtained for improvements in this branch of the manufacture are not yet specified. He next points out the perfectly homogeneous character of cast-steel—its freedom from sand cracks and flaws—and its greater cohesive force and elasticity, compared with the blister steel from which it is made, qualities which it derives solely from its fusion and formation into ingots—all of which properties malleable iron acquires in like manner, by its fusion and formation into ingots in the new process. Nor must it be forgotten that no amount of rolling will give to blistered steel (although formed of rolled bars) the same homogeneous character that cast-steel acquires, by a mere extension of the ingot to some ten or twelve times its original length.

"One of the most important facts connected with the new system of manufacturing malleable iron is, that all the iron so produced will be of the quality known as charcoal iron, not that any charcoal is used in its manufacture, but because the whole of the processes following the smelting of it are conducted entirely without contact with, or the use of any mineral fuel; the iron resulting therefrom will, in consequence, be perfectly free from those injurious properties which that description of fuel never fails to impart to iron that is brought under its influence. At the same time, this system of manufacturing malleable iron offers extraordinary facility for making large shafts, cranks, and other heavy masses; it will be obvious that any weight of metal that can be founded in ordinary cast-iron, by the means at present at our disposal, may also be founded in molten malleable iron, and be wrought into the forms and shapes required, provided that we increase the size and power of our machinery to the extent necessary to deal with such large masses of metal. A few minutes' reflection will shew the great anomaly presented by the scale on which the processes of iron-making are at present carried on. The little furnaces originally used for smelting ore have, from time to time, increased in size, until they have assumed colossal proportions, and are made to operate on 200 or 300 tons of material at a time, giving out 10 tons of fluid metal at a single run. The manufacturer has thus gone on

increasing the size of his smelting furnaces, adapting to their use the blast apparatus of the requisite proportions, and has by this means lessened the cost of production, in every way ensuring a cheapness and uniformity of production, that could never have been secured by a multiplicity of small furnaces. While the manufacturer has shewn himself fully alive to these advantages, he has still been under the necessity of leaving the succeeding operations to be carried out on a scale wholly at variance with the principles he has found so advantageous in the smelting department. It is true that, hitherto, no better method was known than the puddling process, in which from 4 cwt. to 5 cwt. of iron is all that can be operated upon at a time, and even this small quantity is divided into homeopathic doses of some 70 lbs. or 80 lbs., each of which is moulded and fashioned by human labour, carefully watched and tended in the furnace, and removed therefrom, one at a time, to be carefully manipulated and squeezed into form. The vast extent of the manufacture, and the gigantic scale on which the early stages of its progress is conducted, it is astonishing that no effort should have been made to raise the after processes somewhat nearer to a level commensurate with the preceding ones, and thus rescue the trade from the trammels which have so long surrounded it. Mr Bessemer then advertises to another important feature of the new process, the production of what he calls semi-steel. At the stage of the process immediately following the boil, the whole of the crude iron has passed into the condition of cast-steel of ordinary quality; by the continuation of the process the steel so produced gradually loses its small remaining portion of carbon, and passes successively from hard to soft steel, and from softened steel to steely iron, and eventually to very soft iron; hence, at a certain period of the process, any quality may be obtained; there is one in particular, which, by way of distinction, he calls semi-steel, being in hardness about midway between ordinary cast-steel and soft malleable iron. This metal possess the advantage of much greater tensile strength than soft iron; it is also more elastic, and does not readily take a permanent set, while it is much harder, and is not worn or indented so easily as soft iron. At the same time it is not so brittle or hard to work as ordinary cast-steel. These qualities render it eminently well adapted to purposes where lightness and strength are specially required, or where there is much wear, as in the case of railway bars, which, from their softness and lamellar texture, soon become destroyed. The cost of semi-steel will be a fraction less than iron, because the loss of metal that takes place by oxidation in the converting vessel is about 2½ per cent. less than it is with iron, but as it is a little more difficult to roll, its cost per ton may fairly be considered to be the same as iron, but as its tensile strength is some thirty or forty per cent greater than bar iron, it follows that for most purposes a much less weight of metal may be used, so that taken in that way the semi-steel will form a much cheaper metal than any we are at present acquainted with.

"In conclusion, Mr Bessemer observes that the facts he has discovered have not been elicited by mere laboratory experiments, but have been the result of operations on a scale nearly twice as great as is pursued in the largest iron-works, the experimental apparatus converting 7 cwt. in thirty minutes, while the ordinary puddling furnace makes only 4½ cwt. in two hours, which is made into six separate balls; while the ingots or blooms are smooth, even prisms ten inches square by thirty inches in length, weighing about as much as ten ordinary puddle balls." (See Addenda, E).

MACHINERY OF THE MANUFACTURE.

The mechanical operations connected with the manufacture of wrought-iron consist of shingling, hammering, rolling, &c., to which we may add the forging of "noses," that is, the forging of those peculiar forms so extensively in demand for steam-engines, railway carriages, and other works, which has lately become a large and important branch of trade.

In tracing the whole of the processes in the manufacture of wrought iron bars and plates, it will not be necessary to enlarge on those practices which have been superseded by more modern and improved machinery. Suffice it then to observe, that formerly the puddled balls were shingled or fashioned into oblong slabs or blooms by the blows of a heavy forge hammer; during this operation, the scoria and impurities which adhered to the balls were separated from the blooms by the force of impact, and then by a series of blows the iron was rendered malleable, dense, and compact. The blooms were then passed through a series of grooved iron rollers, which reduced them to the form of long, slender iron bars.

These were cut up and piled regularly together or fag-otted, and brought to a welding heat in the heating or balling furnace, when they were again passed several times through grooved rollers, and by this latter process were made into bars or plates ready for the shears.

In order to arrive at a clear conception of the mechanical operations employed in the manufacture of iron, it will be necessary to describe more at length the processes as at present practised, with the improved and powerful machinery now employed; and as much depends upon the application of the motive power, the steam-engine claims the first notice. Until of late years, the vertical steam-engine was invariably used for giving motion to the forge hammer and rolling mill, which were placed on one side of the fly-wheel and the crank on the other; but the high-pressure, non-condensing engine is found to be decidedly preferable, as the waste heat passing off with the products of combustion from the puddling and heating furnaces, is quite sufficient to raise the steam for working the rolls and one of Brown's bloom squeezers, as shown in the following drawing.

In this arrangement the cylinder A (figs. 21, 22, 23), is placed horizontally, and is supplied with steam from

Fig. 21.

boilers near the puddling furnaces. The piston and slides B, and connecting rod C, give motion to the crank shaft D, on which is fixed a heavy fly-wheel E. The puddling rolls F are driven direct from the end of the fly-wheel shaft, and the bloom squeezers H, by a train of spur wheels GG. Under the lower rolls of the squeezers a

Jacob's ladder or elevator I is fixed, for raising the block which has been deprived of its impurities, and reduced to an oblong shape by passing between the rollers of the squeezer. The block, on leaving the rollers, is carried in front of one of the projecting divisions of the ladder and thrown on to the platform in front of the rolls;

the workman then seizes it with a pair of tongs and forces it into the largest groove in the rolls; it is then passed in succession through the other grooves till it attains the required form of the bar.

The drawings of Brown's bloom squeezers, figs. 24, 25, and 26, will sufficiently explain how the heated ball of

puddled iron, K, thrown on the top, is gradually compressed between the revolving rollers as it descends and at last emerges at the bottom, where it is thrown on to the moveable "Jacob's ladder," by which it is elevated to the rolls, as already described. This machine effects a considerable saving of time; will do the work of 12 or 14 furnaces, and may be kept constantly going as a feeder to one or two pairs of rolls. There are two distinct forms of this machine, one as shown in fig. 24, where the bloom receives only two compressions; and the other, which is much more effective, where it is squeezed four times before it leaves the rolls and falls upon the Jacob's ladder, as exhibited in figs. 25, and 26.

There are two other machines for preparing the blooms Horizontal by compression. One is a table firmly embedded in masonry, as shown at AA, in fig. 27, with a ledge rising up from it to a height of about two feet, so as to form an open box. Within this is a revolving box C, of a similar character, much smaller than the last and placed eccentrically in regard to it. The ball or bloom D is placed between the innermost revolving box C and the outer case AA, where the space between them is greatest, and is carried round till it emerges at E, compressed and fit for the rolls.

Another instrument, fig. 28, used for the same purpose, The Alligator acts as a pair of pliers, and squeezes the iron between two flat blades AA. This machine is called the Alligator, and is probably more effective than the horizontal machine, but it requires an attendant to keep the bloom rolling about under the jaws AA, and is, in other respects, inferior to Brown's patent squeezer.

We have stated that the horizontal, non-condensing Advan- steam-engine, from its compact form and convenience of ages of handling, is admirably adapted for giving motion to the machinery of iron-works. For this object, it is superior to the beam-engine, as its speed can be regulated with the horizontal engine.

The manufacture of iron, to suit all the requirements of the manufacture, under the varied conditions of the pressure of the steam, and

the power required for rolling heavy plates and bars, or those of a lighter description. It is also much cheaper in its original cost, and all its parts being fixed upon a

large bed-plate, require a comparatively small amount of masonry to render it solid and secure.

carefully selected and mixed with Welsh No. 1 or No. 2, and Staffordshire No. 2. This latter descrip-

In regard to the manufacture of the rollers for the puddling, boiler-plate, and merchant train, the greatest care must be observed in the selection of the iron and the mode of casting. In Staffordshire there are roller-makers, but in general the manufacturer casts his own, and as much depends upon the metal, the strongest qualities are

tion of iron, when duly prepared, exhibits great tenacity, and is well adapted, either in the first or second melting, for such a purpose. In casting, the moulds are prepared in loam, and when dry are sunk vertically

into the pit to a depth of about 5 feet below the floor. The moulding box is surrounded by sand firmly consolidated by beaters, and a second mould or head is placed above it, which receives an additional quantity of iron to supply the space left by shrinking, and keep the roll under pressure until it solidifies, and thus secures a great uniformity and density in the roller. The metal is run into the mould direct from the air furnace by channels cut in the sand, and immediately the mould is filled, the workman agitates the metal with a rod, in order to consolidate the mass and get rid of any air or gas which may be confined in the metal. This stirring with iron rods is continued till the metal cools to a semi-fluid state, when it is covered up and allowed slowly to cool and crystallize. This slow rate of cooling is necessary to favour an uniform degree of contraction, as the exterior closes up like a series of hoops round the core of the casting, which is always the most porous and the last to cool. In every casting of this kind it is essential to avoid unequal contraction, and this cannot be accomplished unless time is given for the arrangement of the particles by a slow process of crystallization. Rollers for

The manufacture of boiler-plates and thin sheet-iron are difficult to cast sound on account of their large size. They are subjected to very great strain, and require to be cast from the most tenacious metals. The bearings or neck should be enlarged, or turned to the shape shown at AA, and the cylindrical part B should be slightly concave, because, when the

slab is first passed through the rollers, it comes in contact with a small portion only of the revolving surface. The central parts of the roller thus become highly heated, whilst their extremities are perfectly cool; the consequence is, that the expansion of the roller is greatest in the middle, and unless this be provided for by a concavity in the barrel, the plates become buckled, that is, both warped and uneven in thickness, and, consequently, imperfect and unfit for the purposes of boiler making. Bar rolls are generally cast in chill, and great care is required to prevent the chill penetrating too deep so as to injure the tenacity of the metal and render it brittle.

Different kinds of rolling mills used in the iron manufacture, and they vary considerably in their dimensions according to the work they have to perform.

The first, through which the puddled iron is passed, we have already described as puddling rolls. There are others for roughing down which vary from 4 to 5 feet long, and are about 18 inches diameter; those for merchant bars, about 2 feet 6 inches to 3 feet long and 18 inches in diameter, are in constant use. The boiler-plate and black sheet-iron rolls are generally of large dimensions; some of them for large plates are upwards of 6 feet long and 18 to 21 inches in diameter; these require a powerful engine and the momentum of a large fly-wheel to carry the plate through the rollers, and not unfrequently when thin wide plates have to be rolled, the two combined prove unequal to the task, and the result is, the plates cool and stick fast in the middle. The greatest care is necessary in rolling plates of this kind, as any neglect of the speed of the engine or the setting of the rolls results in the breakage of the latter, or bringing the former to a complete stand.

The speed of the different kinds of rolling mills varies according to the work they have to perform. Those for merchant bars make from 60 to 70 revolutions a minute, whilst those of large size for boiler-plates are reduced to 28 or 30. Others, such as the finishing and guide rollers, run at from 120 to 400 revolutions a minute. In Staffordshire, where some of the finer kinds of iron are prepared for the manufacture of wire, the rollers are generally made of cast-steel, and run at a high velocity; such is the ductility of this description of iron, that in passing through a succession of rollers, it will have elongated to 10 or 15 times its original length, and when completely finished, will have assumed the form of a strong wire $\backslash frac\{3\}\{8\}$ to $\backslash frac\{1\}\{4\}$ of an inch in diameter, and 40 to 50 feet in length.

A high temperature is an indispensable condition of success in rolling. The experience of the workman enables him to judge, from the appearance of the furnace, when the pile is at a welding heat, so that when compressed in the rolls the particles will unite. Sometimes it is necessary to give a fine polish or skin to the iron as it leaves the rolls, but this can only be done when the iron cools down to a dark-red colour, and by the practised eye of an intelligent workman.

The above operations would still be incomplete unless the ironmaster had means of cutting the bars and plates to any required size and shape. The machinery for this purpose has of late been brought to a high

degree of perfection, both in regard to power and precision.

The circular saw has been successfully applied for squaring and cutting the larger descriptions of bars, and does its work, particularly in railway bars, with almost mathematical precision. This machine consists of a cast-iron frame or bed AA, fig. 29, bolted down to a solid found-

Fig. 29.

dation, on the ends of which slide two frames BB to support the bar to be cut. The two circular saws or cutters CC are driven by straps passing over the pulleys DE, and rotate at the rate of 800 to 1000 revolutions per minute. The machine is set in motion by transferring the straps from the loose pulley D to the fast pulley E, and as soon as the required speed is attained, the frame BB is carried forward, and the bar FF along with it, by a lever G or eccentric motion, till the bar is cut through. The rate of cutting or pressure upon the saws may be regulated either by hand or weight; care must, however, be taken not to allow the saws to become too hot, and this is provided against by running them in a trough of water. By this process it is evident that the bar must always be cut square at the ends and correctly to the same length. (See Addenda, F).

A great variety of shears are used for cutting iron, bar and scrap iron shears. Some driven by cams or eccentrics, and some by connecting-rods and a crank on the revolving shaft. In large iron-works it is necessary to have two or three kinds, some for cutting up scrap iron and bars for piling, and others for boiler-plates. Of the first we may notice two, one shown in fig. 30, cuts on both sides at AA, and is driven

Fig. 30.

by a crank and connecting-rod B. This machine is chiefly used for cutting puddled bars from the puddling rolls, or any work required for shingling. The next machine, fig. 31, receives motion in the same manner, and also cuts on both sides, the cutters being fixed on the lever and moving with it. This is used for the same purpose as the last, and likewise for cutting scrap iron.

These machines are extensively used in the manufacture of iron, and before the introduction of the plate shears, they

Fig. 31.

were used, with some modifications, to cut boiler-plates, but the work was very imperfectly executed.

The demand for plates of large dimensions and greatly increased weight, such as those for the front and tube plates of locomotive and marine boilers, and those for

tubular and plate bridges, created great difficulties, not only in piling, heating, and rolling, but also in cutting the plates accurately to the required size. To meet these demands, and more particularly for the manufacture of the large plates employed in the cellular top of the Britannia and Conway tubular bridges, Messrs G. B. Thornycroft and Co. constructed a large shearing machine which cut upwards of 10 feet at one stroke. These shears have now come into general use, and are of great importance, on account of the accuracy with which they cut plates of large dimensions, square and even. Figs. 32 and 33 represent this machine; a a a is the standard and table on which the plate is fixed. This table slides forward at right angles to the shears or cutters AAA* A*. The top cutter descending by the action of three eccentrics c c c, which press upon the top of the frame B as it revolves, and force it down, and by one stroke, the knife AA cuts through the whole length of the plate, perfectly clean and straight. The plate is then reversed, the newly cut edge being held against the slopes, and the sliding frame again moved forward to the required width of the plate, when another stroke cuts the other side as before. The rapidity with which the plates are cut is another advantage of this machine, as great as the precision of its cut, and when the immense quantity of plates daily produced at Messrs Thornycroft and Co.'s works are considered, its importance becomes evident.

Fig. 32.—Elevation.

Fig. 33.—Side View.

At the Paris Universal Exhibition of last year (1855), a plate-cutting machine was exhibited, from the United States of America, which appears to effect the same operation as Messrs Thornycroft and Co.'s. It consists of a strong cast-iron frame, nine or ten feet wide, having inserted along its face a steel plate, on which the iron to be cut rests and is held firmly by a faller, which descends on the upper side of the plate. On the same side of the frame a revolving steel cutter, about nine inches in diameter, traverses the whole length of the frame, and in its passage cuts the plate, by compression, in a perfectly straight line, corresponding with the steel edge below. Cutting and shaving plates by a revolving disc has been long in use, but the traversing motion in this machine is certainly new, and its application very creditable to the ingenuity of the inventor. The travelling cutter, which requires great power when cutting thick plates, is driven by a strap over a pulley at one end of the machine, and looking at the work it has to perform and the complexity of its parts, we should consider it less effective and more liable to derangement than the simple and powerful machine of Messrs Thornycroft.

Having thus traced the processes for the conversion

of crude into malleable iron, and the machinery employed, it only remains to give a general summary of the whole. As regards the arrangement of large iron-works, the general principle should be for the machinery to be classed and fixed in the order of the different processes, so that the products of one machine should pass at once to the next, and, in fact, the crude iron should be received at one end, and having passed through all the processes, delivered at the other in the manufactured state.

The crude iron from the smelting furnace is either refined and puddled, or subjected to the boiling process, to get rid of the combined carbon and render the iron malleable; it is then shingled by the forge hammer, by the "alligator," by Brown's squeezer, or by the other machines which have been invented for this purpose. It is then at once passed through the puddling rolls, where it is reduced to the form of a flat bar, and is then cut into convenient lengths by the shears. These pieces are again piled or faggoted together into convenient heaps and re-heated in the furnace. As soon as a faggot thus prepared has been heated to the welding temperature, it is passed through the roughing rolls to reduce it to the form of a bar, and then through the finish-

Fig. 34.—Elevation.

ing rolls, where the required form and size is given to it, either round or square bars, &c. These are straightened and cut to the required sizes, and are then ready for delivery. In most large works all these operations are carried on simultaneously with the smelting process, and in some with extensive mining operations for procuring the coal, ore, and limestone required to supply a production of several thousand tons of manufactured iron per month.

THE FORGE.

The forging of iron has entered, of late years, so largely

into the constructive arts, that the manufactures, however perfect in the rolling-mill, would be very imperfect indeed without the forge. To the discussion of this part of the subject there are many inducements, and we cannot but wonder at the many devices, and the numerous contrivances which present themselves for the attainment of the operations of the forge. In effecting these objects, Mr Nasmyth's steam-hammer is evidently the most effective, and to that instrument we are indebted for the formation and welding of iron upon a scale previously unknown to the workers in that metal.

Mr Nasmyth took out his patent for this invention

The manu- in 1833; and from that time up to the present, it has
factory of iron. maintained its ground against every innovation, and has
performed an important duty in almost every well-regu-
lated work in Europe. It consists of an inverted cylin-

der D, figs. 34 and 35, through which the piston-rod E The manu-
passes, attached to the hammer-blade F by means of bars
and cross-key k, which press upon an elastic packing, to
soften the blow of the hammer, which in heavy forgings
factory of iron.

and heavy blows, operates severely upon the piston-rod. The hammer-block FF is guided in its vertical descent by two planed guides or projections, extending the length of the side-standards AA, between which the hammer-block slides. The attendant gives motion to the hammer by admitting steam from the boiler to act upon the under side of the piston, by moving the regulator I by the handle d. The length of stroke is regulated by increasing or diminishing the distance between the cam N and the valve lever O o, by turning the screws P and U by the bevil wheels q q. The lever O o operates by the cam N coming in contact with the roller o. As soon as this contact takes place, the further admission of steam is not only arrested, but its escape is at the same time effected, and the hammer, left unsupported, descends by its gravity upon the work on the anvil with an energy due to the height of the fall. From this description, it will be seen that the movement of the roller o causes the shoulder of the rod P to get under the point of the trigger catch U; the valve is by these means kept closed till the whole force of the blow is struck. The instant the operation is effected, the concussion of the hammer causes the latch X to knock off the point of the trigger from the shoulder on the valve-rod P, by means of the bent lever s r, and the instant this is accomplished, the valve is re-opened to admit the steam below the piston, by the pressure of steam on the upper side of the small piston in the cylinder M, forcing down the valve rod, which, in this respect, is the active agent for opening the valve.

To arrest the motion of the hammer, it is only necessary to shut the steam-valve; during the process of forging, it is, however, desirable to give time between the blows, to enable the workman to turn and shift his work on the anvil; and to effect this reduced motion, the trigger U is held back from the shoulder of the valve-rod P, by the handle y, which at the same instant opens the valve in the case J, and thus the action of the steam in the cylinder D retards the downward motion of the hammer. The result of these changes is an easy descent of the hammer, which vibrates up and down without touching the anvil, but ready for blows of any severity the instant the trigger is elevated above the shoulder of the valve lever P. From this description, it will appear evident that Mr Nasmuth's invention is one of the most important that has occurred in the art of forging iron. It has given an impetus to the manufacture, and affords facilities for the welding of large blocks of malleable iron that could not be accom-

plished by the tilt and helve hammers formerly in use; and we have only to instance the forging of the stern-posts and cutwaters of iron ships; the paddle-wheel and screw-shafts of our ocean steamers, some of them weighing upwards of 20 tons, to appreciate the value, as well as the intensity of action of the steam-hammer.

In addition to the machinery of the forge, the V anvil, the natural offspring of the steam-hammer, came into existence from the same fertile source. It is chiefly employed for forging round bars and shafts, and may be thus described, A being a section of the round bar or shaft to be forged, B the anvil-block, and C the hammer. From this, it is obvious that, in place of the old plan, where the work is forged upon flat surfaces, as shewn in the annexed figure, and where the blows are diverging,

the effect of the V anvil is a converging action, thus consolidating the mass, and enabling the forger to retain his work directly under the centre of the hammer. This is the more strikingly apparent, as the blows of the hammer upon a round shaft have the effect of causing the mass to assume the elliptical form, forcing out the sides as at AA in every successive blow, and this again, when turned, produces a spongy, porous centre, as shewn in fig. 38. This process is, however, more clearly exemplified in Ryder's forging machines, where all the anvils are of the V form, for the forging of spindles, round bars, and bolts.

The next important discovery in the art of forging, is that of Mr Ryder's machine, patented some years since, for forging small articles, which, on account of the rapidity and precision of its operations, demands a notice in passing. It consisted essentially of a series of small anvils about three inches square, supported from below by large screws passing through the frame of the machine. This screw was employed in order that the distance between the hammer and anvil might be accurately adjusted. Between the screw and the anvil, a stuffing of cork was introduced to deaden the effect of the blow. The hammers were arranged over the anvils, and slid up and down in the frame of the machine. The blow was effected by the revolution of an eccentric, acting

The manufacture of iron, by means of a cradle on the hammer-head, the hammer, however, being lifted again by a strong spiral spring. The hammers made about 700 strokes a-minute. At the side of the machine was a cutter or shears worked

by a long lever; with this the articles were cut to the required length as they were finished. Figs. 39 and 40 represents this machine as improved by Messrs Platt Brothers of Oldham. A A A A are the

Fig. 39.—Elevation of Ryder's Forging Machine.

anvils supported on a wedge B, instead of the screw, as in Ryder's. This substitution was made because the blows of the hammer tore off the threads of the screw, and the machine soon got out of order. The distance between the hammer and anvil is regulated by forcing forwards the wedge B by the rack and pinion C. The cork was then found insufficient as a stuffing, and an immensely strong spring D was substituted; this spring is formed of a band of steel 1½ inches broad, and ¾ inch thick, coiled in a close spiral 2 inches in diameter, and 6½ long; it answers its purpose admirably. The hammers are shown at HHHH, supported by springs, one of which

is seen in the section at E. The eccentrics GGGG, driven by the shaft FF, in their revolution force down the cradles KKKK, which in their turn act on the tops of the hammers, the springs (E) keep the hammer-head always in contact with the cradles KK. The shaft FF is driven by a strap on the pulley LL. It is evident that, by the revolution of the shaft, the eccentric forces down the hammer, and then allows the spring to lift it again; the rapidity of the strokes is only limited by the power of the spring E to keep the hammer in contact with the cradle; if the eccentric revolves too fast, a violent jerking motion is produced. In Mr Ryder's machine,

The manufacture of iron. 700 strokes a-minute was the maximum; but Messrs Platt Brothers, by increasing the strength of the spring, run as high as 1100. A pair of knife edges, worked by the machine itself, has also been substituted for the hand-

iron into the malleable state, it assuredly is not unreasonable to look forward to still greater improvements in the manipulations of the forge. The manufacture of iron.

shears. These perform the work more rapidly and accurately than before, and leave the workman more at liberty. Dies are let into the surfaces of the hammers and anvils, which shape the iron as required.

The rapidity with which this machine executes all kinds of intricate work is truly remarkable; for instance, a bar about $2\backslash frac\{1\}\{2\}\; \backslash times\; 2\backslash frac\{1\}\{2\}$ inches, will be reduced to $1\backslash frac\{1\}\{2\}\; \backslash times\; 10$ inches, and cut off in a minute. Set screws, bolts, spindles, and all kinds of small work are produced at the same rate. Its precision is very effective; the articles are almost as true as if turned in a lathe, and very accurate as to size and weight. Other machines, called "lifts," have been, and continue to be, used for forging a variety of forms and "uses;" but as these partake more or less of the principle employed in Ryder's machine, it will not be necessary to furnish further examples.

In conclusion, we may observe that the facilities afforded by the present age for the forging of malleable iron, are without a parallel in the history of that material. Every known resource has been adopted, and every contrivance and device has been employed to meet the demands of a large and an intricate trade; and looking at the present resources of the country, and the admirable mechanical contrivances for the conversion of crude

IV.—THE STRENGTH AND OTHER PROPERTIES OF IRON.

In this section we have to consider the tensile and transverse strengths and powers of resisting compression of cast and malleable iron, as determined by direct experiment upon specimens of the material; and also to examine whether, as has been alleged, the hot-blast process injures the tenacity of the metal.

CAST IRON.—The following tables give the results of experiments undertaken by Mr Hodgkinson and Mr Fairbairn at the request of the British Association, to determine the tensile and transverse strengths of cast-iron derived from the hot and cold blast. The castings for ascertaining the tensile strain were made very strong at the ends, with eyes for the bolts to which the shackles were attached; the middle part, where it was intended that the specimen should break, was cast of a cruciform + transverse section. The four largest castings were broken by the chain-testing machine belonging to the corporation of Liverpool, the others by Mr Fairbairn's lever.

TABLE I.—Results of the Experiments on the tensile strength of Cast-Iron.

From the same series of experiments we select the following tables, giving the results obtained in regard to the resistance opposed to compression by cast-iron. The specimens employed were cylinders and prisms of various dimensions, and having their faces turned accurately parallel to each other and perpendicular to the axis of the specimen. They were crushed by a lever between parallel steel discs.

TABLE II.—Weights required to crush cylinders, &c., of Carron Iron, No. 2, Hot-Blast.

The specimens of Carron iron in table IV. were prisms, whose base was $\backslash frac\{3\}\{4\}\; \backslash times\; \backslash frac\{3\}\{4\}\; =\; \backslash frac\{9\}\{16\}$ inch, and whose height varied from $\backslash frac\{1\}\{2\}$ inch to 1 inch. The other specimens were cylinders, whose diameter was about $\backslash frac\{1\}\{2\}$ inch, and height varied from $\backslash frac\{1\}\{2\}$ inch to 2 inches.

From the above experiments, Mr Hodgkinson concludes that "where the length is not more than about three times the diameter, the strength for a given base is pretty nearly the same." Fracture took place either by wedges sliding off, or by the top and bottom forming pyramids, and forcing out the sides; and the angle of the wedge is nearly constant, a mean of 21 cylinders being $55^\{\backslash circ\}\; 32\text{'}$.

From the same series of experiments we give the results obtained by Mr Fairbairn, in regard to the effects of time and temperature. The bars employed were cast to be 1 inch square, and 4 feet 6 inches long, and were loaded with permanent weights as under; the deflections being taken at various intervals during a period of fifteen months. Coed-talon hot and cold-blast iron was employed.

It has been assumed by most writers on the strength

of materials, that the elasticity of cast-iron remained the same to the extent of one-third the weight that would break it. This is, however, a mere assumption, as it has been found that the elasticity of cast-iron is injured with less than one-half that weight, and the question to be solved in the above experiments was, to what extent the material could be loaded without endangering its security; or how long it would continue to support weights, varying from one-half to one-tenth of the load that would produce fracture. These experiments were continued from six to seven years, and the results obtained were, that the bars which were loaded to within $\backslash frac\{1\}\{3\}$ of their breaking weight, would have continued to have borne the load, in the absence of any disturbing cause, ad infinitum; but the effect of change, either of the same or a lighter load led ultimately to fracture.

From these facts it is deduced, that so long as the molecules of the material are under strain (however severe that strain may be), they will arrange and accommodate themselves to the pressure, but with the slightest disturbance, whether produced from vibration or the increase or diminution of load, it becomes, under these influences, only a question of time when rupture ensues.

In the following experiments on the relative strengths of coed-talon hot and cold-blast iron to resist transverse strain at different temperatures, the results are reduced to those of bars 2 feet 3 inches between supports, and 1 inch square, as follows:—

From the above it will be seen "that a considerable failure of the strength took place after heating the No. 2 iron from $26^\{\backslash circ\}$ to $190^\{\backslash circ\}$. At $212^\{\backslash circ\}$, we have in the No. 3 a much greater weight sustained than by No. 2 at $190^\{\backslash circ\}$; and at $600^\{\backslash circ\}$ there appears, in both hot and cold-blast, the anomaly of increased strength as the temperature is increased."¹ The above results are, with one exception, in favour of the cold blast, as far as strength is concerned; and in favour of the hot blast, with one exception, as regards power of resisting impact.

The following table gives the results of Mr Fairbairn's experiments on the transverse strength of rectangular cast-iron bars, each bar being reduced to exactly one inch square.

"In the following abstract, the transverse strength, which may be taken as a criterion of the value of each iron, is obtained from the mean of the experiments first on the long bars, 4 feet 6 inches between the supports, and next on those of half the length, or 2 feet 3 inches between supports."

"All the other values are deduced from the 4 feet 6 inches bars."

¹ This probably arises from the greater ductility of the bars at an increased temperature.

* The irons with asterisks are taken from the experiments on hot and cold blast iron made by Mr Hodgkinson and Mr Fairbairn for the British Association for the Advancement of Science. See Seventh Report, vol. vi.

The modulus of elasticity was usually taken from the deflection caused by 112 lbs. on the 4 feet 6 inch bars. To find from the above the breaking weight in rectangular bars generally: calling $b$ and $d$ the breadth in inches, and $l$ the distance between the supports in feet; and putting 4.5 for 4 feet 6 inches, we have $\backslash frac\{4.5\; b\; d^2\; S\}\{l\}\; =$ breaking weight in lbs. The value of $S$ being taken from the table above.

For Example:—What weight would be necessary to break a bar of Lowmoor iron, 2 inches broad, 3 inches deep, and 6 feet between the supports? According to the rule given above we have $b=2$ inches, $d=3$ inches, $l=6$ feet, $S=472$, by the table. Then $\backslash frac\{4.5\; \backslash times\; 2\; \backslash times\; 3^2\; \backslash times\; 472\}\{6\}\; =\; 6372$ lbs.

† This iron was melted in the cupola, from coke entirely freed from sulphur, by Mr C. Calvert's process.

The manufacture of iron. With regard to the comparative strengths of hot and cold-blast iron, the following extracts from Mr Hodgkinson's report, read before the British Association, give the general results of his experiments:—

“Beginning with No. 1 iron, of which we have a specimen from the Buffery Iron-Works, a few miles from Birmingham, we find the cold-blast iron somewhat surpassing the hot-blast in all the following particulars: direct tensile strength, compressive strength, transverse strength, power to resist impact, modulus of elasticity or stiffness, specific gravity; whilst the only numerical advantage possessed by the hot-blast iron is, that it bends a little more than the cold-blast before it breaks.

“In the irons of the quality No. 2, the case seems in the same degree different; in these the advantages of the rival kinds seem to be more nearly balanced. They are still, however, rather in favour of the cold-blast.

“So far as my experiments have proceeded, the irons of No. 1 have been deteriorated by the hot-blast; those of No. 2 appear also to have been slightly injured by it, while the irons of No. 3 seem to have benefited by its mollifying powers. The Carron iron No. 3 hot-blast, resists both tension and compression with considerably more energy than that made with the cold-blast; and the No. 3 hot-blast iron from the Devon works, in Scotland, is one of the strongest cast irons I have seen, whilst that made by the cold-blast is comparatively weak, though its specific gravity is very high, and higher than in the hot. The extreme hardness of the cold-blast Devon iron above prevented many experiments that would otherwise have been made upon it, no tools being hard enough to form the specimens. The difference of strength in the Devon irons is peculiarly striking.

“From the evidence here brought forward, it is rendered exceedingly probable that the introduction of a heated blast in the manufacture of cast iron has injured the softer irons, whilst it has frequently mollified and improved those of a harder nature, and, considering the small deterioration that the irons of quality No. 2 have sustained, and the apparent benefit to those of No. 3, together with the great saving effected by the heated blast, there seems good reason for the process becoming as general as it has done.”

The following table gives a general summary of the results of Mr Fairbairn's experiments on the strength of iron after successive meltings. The iron used was Eglington No. 3 hot-blast, and was melted eighteen times, three bars being cast at each melting. These bars, which were about 1 inch square and 5 feet long, were placed upon supports 4 feet 6 apart, and broken by a transverse strain. Cubes, from the same irons, exactly 1 inch square, were then crushed between parallel steel bars, by a large wrought-iron lever.

In the following Table XIII., the results on transverse strain are reduced to those on bars exactly 1 inch square and 4 feet 6 inches between supports.

In the above results it will be observed that the maximum of strength, elasticity, &c., is only arrived at after the metal has undergone twelve successive meltings. It is probable that other metals and their alloys may follow the same law, but that is a question that has yet to be solved, probably by a series of experiments

The manufacture of iron requiring a considerable amount of time and labour to accomplish, but which we may venture to hope will be shortly forthcoming from the same author.

In the resistance of the different meltings from the same iron, to a force tending to crush them, we have the following results.

Nearly the whole of the specimens were fractured by wedges which split or slid off diagonally at an angle of from $52^\{\backslash circ\}$ to $58^\{\backslash circ\}$.

MALLEABLE IRON.—The greatly extended application of wrought iron to every variety of construction renders an investigation of its properties peculiarly interesting. It is now employed more extensively than cast iron; and, on account of its ductility and strength, nearly two thirds of the weight of material may in many cases be saved by its employment, while great lightness and durability are secured. Its superiority is especially evident in constructions where great stiffness is not required, but on the other hand any degree of rigidity may be obtained by the employment of a tubular or cellular structure, and this may be seen in the construction of wrought iron tubular bridges, beams, and iron shops. The material of malleable iron which is making such vast changes in the forms of construction, cannot but be interesting and important, and considering that the present is far from the limit of its application, we shall endeavour to give it that degree of attention which the importance of the subject demands.

From the forge and the rolling mill we derive two distinct qualities of iron, known as "red short" and "cold short." The former is the most ductile, and is a tough fibrous material which exhibits considerable strength when cold; the latter is more brittle, and has a highly crystalline fracture almost like cast-iron; but the fact is probably not generally known, that the brittle works as well and is as ductile under the hammer as the other when at a high temperature.

Mr Charles Hood, in a paper read some time ago before the Institute of Civil Engineers, went into the subject of the change in the internal structure of iron, independently of and subsequently to the processes of its manufacture. After adducing several instances of tough fibrous malleable iron becoming crystalline and brittle during their employment, he attributes these changes to the influence of percussion, heat, and magnetism, but questions whether either will produce the effect per se. Mr Hood continues, "The most common exemplification of the effect of heat

in crystallizing fibrous iron is, by breaking a wrought-iron furnace bar, which, whatever quality it was of in the first instance, will in a short time invariably be converted into crystallized iron, and by heating and rapidly cooling, by quenching with water a few times any piece of wrought iron, the same effect may be far more speedily produced. In these cases we have at least two of the above causes in operation—heat and magnetism. In every instance of heating iron to a very high temperature, it undergoes a change in its electric or magnetic condition; for at very high temperatures iron loses its magnetic powers, which return as it gradually cools to a lower temperature. In the case of quenching the iron with water, we have a still more decisive assistance from the electric and magnetic forces; for Sir Humphrey Davy long since pointed out that all cases of vaporization produced negative electricity in the bodies in contact with the vapour; a fact which has lately excited a good deal of attention in consequence of the discovery of large quantities of negative electricity in effluent steam." Mr Hood then proceeds to the subject of percussion. "In the manufacture of some descriptions of hammered iron, the bar is first rolled into shape, and then one-half the length of the bar is heated in a furnace, and immediately taken to the tilt hammer and hammered, and the other end of the bar is then heated and hammered in the same manner. In order to avoid any unevenness in the bar, or any difference in its colour where the two distinct operations have terminated, the workman frequently gives the bar a few blows with the hammer upon that part which he first operated upon. That part of the bar immediately becomes crystallized, and so extremely brittle that it will break to pieces by merely throwing it on the ground, though all the rest of the bar will exhibit the best and toughest quality imaginable. This change, therefore, has been produced by percussion (as the primary agent) when the bar is at a lower temperature than the welding heat. Here it must be observed that it is not the excess of hammering which produces the effect, but the absence of a sufficient degree of heat, at the time that the hammering takes place; and the evil may probably be all produced by four or five blows of the hammer if the bar happens to be of a small size. In this case we witness the combined effects of percussion, heat, and magnetism. When the bar is hammered at the proper temperature, no such crystallization takes place, because the bar is insensible to magnetism; but as soon as the bar becomes of that lower degree of temperature at which it can be affected by magnetism, the effect of the blows it receives is to produce magnetic induction, and that magnetic induction and consequent polarity of its particles, when assisted by further vibrations from additional percussion, produces a crystallized texture."

The crystallization of perfectly fibrous and ductile wrought-iron has long been a subject of dispute, and although we agree with most of Mr Hood's views, we are not altogether prepared to admit that the causes assigned are the only ones concerned in producing the change, or that more than one is necessary. On the occasion of the accident on the Versailles Railway some years since, the whole array of science and practice were brought to bear upon the elucidation of the cause. Undoubtedly the broken axle presented a crystalline fracture, but it has never been ascertained how far heat and magnetism were in operation as in the case of an axle, and more especially a crank-axle, the constant vibration caused by irregularities in the way and the weight of the engine appears to be quite sufficient to occasion the breakage without aid from the other forces. Undoubtedly in almost all cases of the sudden fracture of axles or

The manufacture of wrought-iron bars, during employment, the fracture presents a crystalline structure, but we believe that any molecular disturbance, such as impact, can effect this, the only question being, how long will the material sustain the action before it breaks.

This question has been attempted to be decided by direct experiment under the direction of the Commission on Railway Structures. It was found that with cast-iron bars subjected to long continued impacts, "when the blow was powerful enough to bend the bars through one-half of their ultimate deflection (that is to say, the deflection which corresponds to their fracture by dead pressure), no bar was able to stand 4000 of such blows in succession. But all the bars (when sound) resisted the effects of 4000 blows, each bending them through one-third of their ultimate deflection. These results were confirmed by experiments with a revolving cam which deflected the bars.

"In wrought-iron bars no very perceptible effect was produced by 10,000 successive deflections by means of a revolving cam, each deflection being due to half the weight which, when applied statically, produced a large permanent flexure." These results agree with those obtained by Mr Fairbairn in regard to the effects of time on loaded bars of cast-iron, already given.

Arago and Wollaston have paid considerable attention to this subject, the latter having been the first to point out that native iron is disposed to break in octahedra and tetrahedra, or combinations of these forms. The law which leads to fracture in wrought-iron from changes in the molecular structure operates with more or less intensity in other bodies; repeated disturbances, in turn destroying the cohesive force of the material by which they are held together. A French writer of eminence, Arago, appears to consider the crystallization of wrought-iron to be due to the joint action of time and vibration, but we think with Mr Hood that time and its duration depends entirely upon the intensity of the disturbing forces, and, moreover, that the time of fracture is retarded or accelerated in a given ratio to the intensity with which these forces are applied.

From the above statements we may safely deduce the fact, that it is essential to the use of this material to consider the purposes to which it is applied, the forms to which it may be subjected, and the conditions under which it may be placed, in order to arrive at just conclusions as to the proportions, in order to afford to the structure (whatever that may be), ample security in its powers of resistance to strain.

On the subject of the strength of wrought-iron, we have before us the researches of Mr Fairbairn, in a paper entitled, "An Inquiry into the Strength of wrought-iron plates and their rivetted joints, as applied to Shipbuilding and Vessels exposed to severe strains."¹ In that communication it is shewn, from direct experiments, that in plates of rolled iron there is no material difference between those torn asunder in the direction of the fibre, and those torn asunder across the fibre. This uniformity of resistance arises probably from the way in which the plates are manufactured, which is generally out of flat bars, cut and piled upon each other, as at A, one-half transversely and the other half longitudinally in the line

of the pile. From this it will be seen that in preparing the bloom or shingle for the rollers, the fibre is equally divided, and the only superiority that can possibly be attained is in the rolling which draws the shingle rather more in the direction of the length of the plate than its breadth.

In the following table we have the results of the experiments. The manufacture of iron.

Or as 22.5, 23.0, equal to about $\backslash frac\{1\}\{3\}$ in favour of those torn across the fibre.

From the above it is satisfactory to know, so far as regards uniformity in the strength of plates, that the liability to rupture is as great when drawn in one direction as in the other; and it is not improbable, that the same properties would be exhibited, and the same resistance maintained, if the plates were drawn in any particular direction obliquely across the fibrous or laminated structure.

From the same author we select the results of a series of experiments on the tensile strength of SC bars of different lengths, and about 1$\backslash frac\{1\}\{2\}$ in diameter. The following tables gives the strains required for each of four successive breakages of the same pieces of iron. These experiments are highly interesting, as they not only confirm those made upon plates, but they indicate a progressive increase of strength, notwithstanding the elongation and the reduced sectional area of the bars. These facts are of considerable value, as they distinctly shew that a severe tensile strain is not seriously injurious to the bearing powers of wrought-iron, even when carried to the extent of or increased four times repeated, as was done in these experiments. In practice it may not be prudent to test bars and chains to their utmost limit of resistance; it is nevertheless satisfactory to know that in cases of emergency those limits may be approached without incurring serious risk of injury to the ultimate strength of the material.

The following abstract gives the results of the experiments:—

"As all these experiments were made upon the same description of iron, it may be fairly inferred that the length of a bar does not in any way affect its strength."

Reduction of the above Table.

¹ Philosophical Transactions, part ii., 1850, p. 677.

"Here it appears that the rate of elongation of bars of wrought-iron increases with the decrease of their length; thus while a bar of 120 inches had an elongation of .216 inch per unit of its length, a bar of ten inches has an elongation of .42 inch per unit of its length, or nearly double what it is in the former case. The relation between the length of and its maximum elongation per unit, may be approximately expressed by the following formula, viz.—

where $L$ represents the length of the bar, and $l$ the elongation per unit of the length of the bar."

The above results are not without value, as they exhibit the ductility of wrought-iron at a low temperature, as also the greatly increased strength it exhibits with a reduced sectional area under severe strain.

On the transverse strength of wrought-iron it will not be necessary to enlarge, as we have numerous examples before us in the experiments undertaken to determine the strength and form of the Britannia and Conway Tubular Bridges.¹ In these experiments will be found an entirely new description of form and construction, which have emanated from them, and which have led to a new era in the history of bridges, and the application of wrought iron to other purposes besides those in connection with buildings, and its greatly extended application to the useful arts. For further information on this subject we refer the reader to Mr Fairbairn's² and Professor Hodgkinson's works, in both of which will be found data sufficient to establish the great superiority of malleable over cast iron, or any other material, either as regards strength or economy in its application.

On the resistance of wrought-iron plates to a force tending to burst them, Rondelet has shown that it requires a force of 70,000 lbs. per square inch to produce fracture, and Mr Fairbairn's experiments proved that a wrought-iron plate of one-quarter of an inch thick resisted a pressure from a ball 3 inches in diameter, equal to that required to rupture a 3 inch oak plank.

At the request of the British Association, Dr. Thomson of Glasgow examined the chemical constitution of hot-blast iron, and he gives the following as the result of his inquiry:—

"(1.) The specific gravity of hot-blast iron is greater than that of cold-blast."

"The following are the specific gravities of eight specimens of cold-blast iron:

"The specific gravity of the Muirkirk iron is considerably less than of that smelted at Carron and the Clyde Iron-Works; the mean of the eight specimens is 6.7034.

"It has been hitherto supposed that the difference between cast-iron and malleable iron consists in the presence of carbon in the former, and its absence from the latter; in other words, that cast-iron is a carburet of iron. But in all the specimens of cast-iron which we analysed we constantly found several other ingredients besides iron and carbon. Manganese is pretty generally present in minute quantity, though in one specimen it amounted to no less a quantity than 7 per cent.; its average amount is 2 per cent. Silicon is never wanting, though its amount is exceedingly variable, the average quantity is about 1½ per cent.; some specimens contained 3½ per cent. of it, while others contain less than a half per cent. Aluminum is very rarely altogether absent, though its amount is more variable than that of silicon. Its average amount is 2 per cent.; sometimes it exceeds 4½ per cent., and sometimes it is not quite 1-5000th part of the weight of the iron.

"Calcium and magnesium are sometimes present, but very rarely. The mass and the quantity does not much exceed 1.5th per cent. In a specimen of men of cast-iron which I got from Mr Nelson, and which he had iron smelted from pyrites, there was a trace of copper, showing that the pyrites employed was not quite free from copper; and in a specimen from the Clyde Iron-Works there was a trace of sulphur. The following table exhibits the composition of six different specimens of cast-iron, No. 1, analyzed in my laboratory, either by myself or by Mr. John Tennent.

"The constant constituents of cold-blast cast-iron, No. 1, are iron, manganese, carbon, silicon, and aluminum. The occasional constituents are copper, sulphur, calcium, and magnesium. These occur so rarely, and in such minute quantity, that we may overlook them altogether.

"The constant constituents occur in the following mean atomic proportions:

"(2.) I examined only one specimen of cast-iron, No. 2. It was an old specimen, said to have come from Sweden, but I have no evidence of the correctness of this statement. Its specific gravity was 7.1633 higher than any specimens of cold-blast iron, No. 1. Its constituents were,

"The presence of sulphur in this specimen leads to the suspicion that it is not a Swedish specimen; for as the Swedish ore is magnetic iron, and the fuel charcoal, the presence of sulphur in the iron is very unlikely."

"In this specimen, the atoms of iron and manganese are to those of carbon, silicon, and aluminum, in the proportion of 4½ to one, instead of 3½ to one, as in cast-iron No. 1.

"The atoms of carbon, silicon, and aluminum, approach the proportions of 7, 2, and 1, so that in cast-iron, No. 2, judging from one specimen, there is a greater proportion of carbon, compared with the silicon and aluminum, than in cast-iron, No. 1.

"Mr. Tennent analysed a specimen of hot-blast iron, No. 2, from Gartsherry. Its specific gravity was 6.9156, and its constituents,

So that it resembles cast-iron, No. 1, in the proportion of its constituents. The carbon is almost the same as in cold-blast iron, No. 2, but the proportion of aluminum is four times as great, while the silicon is little more than half as much. The atomic ratios are, carbon, 4; silicon, 0.67; aluminum, 2.28.

"3. Five specimens of hot-blast cast-iron, No. 1, were analysed. Two of these were from Carron, and three from the Clyde Iron-Works, where the hot-blast originally began; and where, of course, it has been longest in use. The specific gravity of these specimens was found to be as follows:

¹ See Mr Fairbairn's and Mr Edwin Clark's works on the Conway and Britannia Tubular Bridges.

² "On the application of cast and wrought iron to building purposes," and "Useful Information for Engineers."

³ I have been told by Mr Mushet that the Swedes add sulphur to their iron No. 2.

"It appears from this, that the hot-blast increases the specific gravity of cast-iron by about 1.22d part. It approaches nearer the specific gravity of cast-iron, No. 2, smelted by cold air, than to that of No. 1.

The following table exhibits the constituents of these four specimens:—

The mean of these analyses gives us,

Or, in the proportion of 64 atoms of iron and manganese to 1 atom of carbon, silicon, and aluminum. In the cold-blast cast-iron we have,

"Thus it appears, that when iron is smelted by the hot-blast its specific gravity is increased, and it contains a greater proportion of iron, and a smaller proportion of carbon, silicon, and aluminum, than when smelted by the cold-blast.

V. THE STATISTICS OF THE IRON TRADE.

This article has already extended so much beyond the limits of our inquiry, that we must confine ourselves to an exceedingly brief notice of the statistics of this important manufacture. In 1740 the iron trade suffered a sudden check from a falling off in the supply of charcoal, coal or coke not having been employed at that time for smelting. The annual production seems to have decreased from 180,000 to about 17,350 tons per annum. This comparatively small quantity was smelted in the following counties, viz.—

Soon afterwards the difficulties in the way of using coal were overcome, and the manufacture extended rapidly. The number of charcoal furnaces decreased, but the quantity produced by each was considerably increased. The following table shows the state of the trade in 1788:—

In the same year were erected and blowing in Scotland the following furnaces:—

About the year 1796 it was contemplated by Mr Pitt to add to the revenue by a tax on coal. This met with a powerful opposition on the part of the manufacturers and consumers, especially those in the iron trade. A committee was appointed, witnesses were examined, and the measure abandoned as unwise and impracticable. The following table exhibits an abstract of the facts collected, and shows the rapid progress of the iron trade in the eight preceding years:—

The following table shows the comparative make of pig iron in 1820 and 1827:—

From that time to the present the manufacture has steadily increased. The following table gives the state of the trade in 1854; the particulars are extracted from the Mining Records, published under the direction of Mr R. Hunt, in connection with the Museum of Practical Geology, London. The importance which Scotland has assumed in reference to the iron manufacture is especially worthy of notice.

In connection with the above, we insert the following table from Mr Kenyon Blackwell's paper on the Iron Industry of Great Britain, read before the Society of Arts. It gives the estimated production of crude iron in the various countries.

In referring to the above, it will be seen that Great Britain produces as much crude iron as all other countries

put together; and a great portion of that iron being converted into bars and plates, indicates a large and important article of production. An article of immense value to the country—of great demand at home and abroad—and justly entitled not only to improvements and economy in its manufacture, but to the generous support of a liberal and an enlightened Government.

(W. F.)

ADDENDA.

(A) Mr Cort's inventions.—It would be a difficult task to enumerate all the services rendered by Mr Cort to the iron industry of this country, or sufficiently to express our sympathies with the descendants and relatives of a man to whose mechanical inventions we owe so much of our national greatness. It is, perhaps, not generally known that Mr Henry Cort expended a fortune of upwards of £20,000 in perfecting his inventions for puddling iron, and rolling it into bars and plates; that he was robbed of the fruit of his discoveries by the villany of officials in a high department of the Government, and that he was ultimately left to starve by the apathy and selfishness of an ungrateful country. When these facts are known, and it has been ascertained that Mr Henry Cort's inventions have conferred an amount of wealth upon the country equivalent to six hundred millions sterling, and have given maintenance and employment to six hundred thousand of the working population of our land for the last three or four generations, we are surely justified in referring to services of such vast importance, and in advocating the principle that substantial proofs of the nation's gratitude should be afforded to rescue from penury and want the descendants of such a benefactor.

(B) The Ores of Belgium.—A species of bog ore is also used, which is said to be found near the surface, and is washed to free it from impurities.

(C) The Calcination of the Ores.—We are informed that the black and clay bands are all calcined in Scotland, even for the hot-blast process, the coaly matter in the black bands being sufficient to effect the calcination without other fuel. The carbonaceous ores lose as much as 40 to 50 per cent. of their weight in the process.

(D) The blast.—The Scotch iron smelters allege that the diffusive power of the blast is increased rather than diminished by increasing the number of blowpipe nozzles, and give as a reason for the use of so many that they can be so much more easily repaired, the stoppage of one not materially affecting the working of the furnace.

(E) Mr Bessemer's process.—Such is the discovery which Mr Bessemer has communicated to the world, but having reason to believe that the products of this new process of conversion have not been sufficiently tested, we deem it essential to reserve our opinion on this important question until further experiments have proved the efficiency of the process. We are the more convinced of the propriety of exercising precaution from the fact that experiments have been made by competent authorities, in which it has been ascertained that the ingots derived from Mr Bessemer's process are not malleable, but highly refined metal, deprived of its carbon, but still requiring to be puddled to fit it for the hammer or the rolls. Should this be the case, the saving effected will not be so great as at first anticipated, and, moreover, it has been asserted by practical men that the heat produced is so intense, as not only to deprive the metal of its carbon, but to injure the tenacity of the iron. Should these statements be correct, it will seriously detract from the merits of a discovery, which at first sight promised the commencement of a new era in the manufacture of iron. It is, however, due to Mr Bessemer to wait for further developments, which may lead to important results before coming to any conclusion as to the merits of his invention. We trust, however, that the practical difficulties which appear to surround the process will ultimately be overcome by a series of well conducted experiments, calculated to determine the full value of the invention.

(F) We are informed that the circular saw for cutting railway bars is frequently driven by the Eolipile or Hero's engine, by which a speed of 2000 revolutions a minute may be attained.

(W. F.)