Of the smelting of iron-ores

—We shall describe, in the first place, the methods practised in Great Britain, and shall afterwards consider those pursued in other countries, in the treatment of their peculiar ores. Iron is divided into three kinds, according to the different metallic states in which it may be obtained; and these are called crude or cast iron ; steel ; and bar or malleable iron. These states are determined e entially by the different proportions of charcoal or carbon held in chemical combination; cast iron containing more than steel, and steel more than malleable iron; which last, indeed, ought to be the pure metal, a point of perfection, however, rarely if ever attained. It is impo ible to a ign the limits between these three forms of iron, or their relative proportions of carbon, with ultimate precision; for bar iron pa es into steel by insensible gradations, and steel and cast iron make such mutual transitions as to render it difficult to define where the former commences, and the latter ceases, to exist. In fact, some steels may be called crude iron, and some cast irons may be reckoned among steels. Towards the conclusion of the last century the manufacture of iron underwent a very important revolution in Great Britain, by the substitution of pitcoal for charcoal of wood, the only combustible previously used in smelting the ores of this metal. This improvement served not merely to diminish the cost of reduction, but it furnished a softer cast iron, fit for many new purposes in the arts. From this era, iron works have a umed an immense importance in our national industry, and have given birth to many ingenious and powerful machines for fashioning the metal into bars of every form, with almost incredible economy and expedition. The profusion of excellent coal, and its a ociation in many localities with iron-stone, have procured hitherto for our country a marked superiority over all others in the iron trade; though now every po ible effort is making by foreign policy to rival or to limit our future operations. In 1802, M. de Bonnard, now divisionary inspector in the royal corps of mines of France, and secretary of the general council, made a tour in England, in order to study our new proce es of manufacturing iron, and published on his return, in the Journal des Mines, tom. 17., a memoir descriptive of them. Since the peace, many French engineers and iron-masters have exerted themselves in naturalizing in France this species of industry; and M. de Gallois, in particular, after a long residence in Great Britain, where he was admitted to see deliberately and minutely every department of the iron trade, returned with ample details, and erected at Saint-Etienne a large establishment entirely on the English model. More recently, MM. Dufrénoy and Elie de Beaumont, and MM. Coste and Perdonnet, have published two very copious accounts of their respective metallurgic tours in Great Britain, illustrated with plans and sections of our furnaces, for the instruction of the French nation. The argillaceous carbonate of iron, or clay ironstone of the coal measures, is the chief ore smelted in England. Some red hematite is used as an auxiliary in certain works in Cumber land and Lancashire; but nowhere is the iron-sand, or other ferruginous matters of the secondary strata, employed at present for procuring the metal. Among the numerous coal-basins of England there are two, in particular, which furnish more than three-fourths of the whole cast iron produced in the kingdom; namely, the coal field of Dudley, in the south of Staff ords hire; and the coal fields of Mon mouths hire, in South Wales, along with those of Gloucestershire and Somersets hire. Dudley is peculiarly favoured by nature. There are found a ociated the coal, the iron ore, the limestone for flux, and the refractory fire-clay for constructing the interior brick-work of the furnaces. This famous clay is mined at Stour bridge, and exported to every part of the kingdom for making cast-steel crucibles and gla -house melting pots. At Merthyr-Tydvil, the centre of the iron works of Wales, the iron-stone is extremely plentiful, forming 16 beds, or rather constituting an integrant portion of 16 beds of slate-clay. Sometimes it occurs in pretty long tables adjoining each other, so as to resemble a continuous stratum; but more frequently it forms nodules of various size and abundance, placed in planes both above and below the coal seam. Eight varieties of ore, belonging to different beds, have been distinguished by the following barbarous names: black balls, black pins, six-inch-wide vein, six-inch jack, blue vein, blue pins, gray pins, seven pins. The bed containing the first quality of iron-stone is analogous to the black ore of Staff ords hire called gubbin ; it is often cleft within like septaria , and its cavities are sometimes besprinkled with crystals of carbonate of lime or quartz. In the superior beds there are nodules decomposing into concentric coats, of which the middle is clay. Crystals of oxide of titanium are occasionally found in the middle of the balls of clay iron-stone; to which the metallic titanium observed in the inside of the dome of blast furnaces, may be traced. Both at Dudley and South Wales, casts of shells belonging to the genus unio , are observed on the iron-stone. The average richne of the iron-stones of South Wales is somewhat greater than those of Staff ords hire. The former is estimated at 33 parts of cast iron, while the latter rarely exceeds 30 parts in 100 of ore; and this richne , joined to the superior quality or cheapne of the coals, and the proximity of the sea, gives South Wales a decided advantage as a manufacturing district. The number of blast furnaces in the parish of Merthyr-Tydvil amounts to upwards of 30. The cast iron produced is, however, seldom brought into the market, but is almost entirely converted into bar iron, of which, at Mr. Crawshay’s works, 600 tons are manufactured in a week. Numerous iron railways, extending through a length of 220 miles, facilitate the transport of the materials and the exportation of the products. That concurrence of favourable circumstances, which we have noticed as occurring at Dudley, prevails in an equal degree in South Wales. The same economy which the use of coal has introduced into the smelting of cast iron from the ore, also extends to its refinery into bars. And this proce would supersede combustible, better for many purposes, particularly the manufacture of steel. In some English smelting works, indeed, where sheet iron is prepared for making tin plate, a mixed refining proce is employed, where the cast iron is made into bar iron by wood charcoal, and laminated by the aid of a coal fire. Till 1740, the smelting of iron ores in England was executed entirely with wood charcoal; and the ores employed were principally brown and red hematites. Earthy iron ores were also smelted; but it does not appear that the clay iron-stones of the coal-basins were then used, though they constitute almost the sole smelting material at the present day. At that era, there were 59 blast furnaces, whose annual product was 17,350 tons of cast iron; that is, for each furnace, 294 tons per annum, and 5 1 ⁄ 8 tons per week. By the year 1788, several attempts had been made to reduce iron ore with coaked coal; and there remained only 24 charcoal blast furnaces, which produced altogether 13,000 tons of cast iron in the year; being at the rate of 546 tons for each per annum, or nearly 11 tons per week. This remarkable increase of 11 tons for 5 1 ⁄ 8 , was due chiefly to the substitution of cylinder blowing machines worked with pistons, for the common wooden bellows. Already 53 blast furnaces fired with coke were in activity; which furnished in to to 48,800 tons of iron in a year; which raises the annual product of each furnace to 907 tons, and the weekly product to about 17 1 ⁄ 2 tons. The quantity of cast iron produced that year (1788) | by means of coal, was | 48,800 | tons, | | and that by wood charcoal, was | 13,100 | | | constituting a total quantity of | 61,900 | tons. | In 1796, the wood charcoal proce was almost entirely given up; when the returns of the iron trade made by desire of Mr. Pitt, for establishing taxes on the manufacture, afforded the following results :— 121 blast furnaces, furnishing in whole per annum 124,879 tons, constituting an average amount for each furnace of 1032 tons. In 1802, Great Britain po e ed 168 blast furnaces, yielding a product of about 170,000 tons; and this product amounted, in 1806, to 250,000 tons, derived from 227 coke furnaces, of which only 159 were in activity at once. These blast furnaces were distributed as follows :— | In the principality of Wales | 52 | | In Staff ords hire | 42 | | In Shropshire | 42 | | In Derby shire | 17 | | In Yorkshire | 28 | | In the counties of Gloucester, Mon mouth, Leicester, Lancaster, Cumber land, and North umber land | 18 | | In Scotland | 28 | | 227 | In 1820, the iron trade had risen to the amount shewn in the following table :— | Tons. | | Wales manufactured, per annum | 150,000 | | Shropshire and Staff ords hire | 180,000 | | Yorkshire and Derby shire | 50,000 | | Scotland, with some places in England | 20,000 | | Total | 400,000 | In a statistical view given by M. de Villefo e, of the French and English iron works, he a igns to the latter, in 1826, 305 blast furnaces, distributed as follows :— | In the principality of Wales | 87 | | In Staff ords hire | 78 | | In Shropshire, Derby shire, Yorkshire, . | 84 | | In Scotland | 56 | | 305 | Out of these, 280 were in activity at the same time; and if we suppose their mean product to have been 50 tons a week, the total product would have been, in 1826, 728,000 tons. But this estimate seems to be somewhat above the truth; for, from the information communicated by Mr. Philip Taylor to M. Achille Chaper, a considerable French iron-master, who, in the summer of 1826, inspected two-thirds of the blast furnaces of Great Britain, their product during this year was about 600,000 tons. The preceding details shew the succe ive increments which the manufacture of cast iron has received; and a similar progre ion has taken place in its refinery into wrought iron. This operation was formerly effected by the agency of wood charcoal in refineries analogous to those still made use of in France. But when that kind of fuel began to be scarce in this island, it came to be mixed with coke in various proportions. The bar iron thus produced was usually hard, and required much time to convert, so that an establishment which could produce 20 tons of bar iron in a week, was deemed considerable. At that time, England imported annually from Sweden and Ru ia the enormous quantity of 70,000 tons of iron. Mr. Cort, to whom Great Britain is indebted for the methods now pursued in this country, succeeded about that time, after many unsucce ful experiments, in converting cast iron into bar iron, by exposing it on the hearth of a reverberatory furnace to the flame of pitcoal. This method, which po e ed the advantage of employing this species of combustible alone, likewise simplified the treatment, because it required no blast apparatus. But this mode of refinery, consisting in the use of a reverberatory furnace alone, did not produce altogether the desired result. It was irregular; sometimes the lo of iron was small, but at others it was very considerable; and there were great variations in the quality of the iron, as well as in the quantity of fuel consumed. Mr. Cort succeeded in removing this uncertainty of result, by causing the puddling in the reverberatory furnace to be preceded by a kind of refinery with coke. The intent of this operation was to decarb urate the iron, and to prepare it for becoming malleable. The metal took in that case the name of finery metal, called, for sake of brevity, fine-metal . He also substituted the drawing cylinders for the extension under the hammer, an improvement which accelerated greatly the manufacture of bar iron. The iron then yielded by the operation of puddling, was of a very inferior quality, and could not be directly employed in the arts. In order to give it more consistence, it was subjected to a second heating in a reverberatory furnace; and whenever this method had arrived at a high enough degree of perfection to afford products fit for the market, it became exclusively employed in Great Britain. This new method of transforming cast-iron into malleable iron, speedily gained such an extension, that of late years, a single iron-work, Cyfartha in Wales, manufactured annually more than twice as much as was made annually from 1740 to 1750, in the whole kingdom. In surveying the improvements which the iron manufacture has received in England in the space of the last 60 years, they are seen to be resolvable into two; the first set relating to the smelting of the ores; the other, to the conversion of the pigs into bar iron; hence naturally arise two heads under which the subject of iron must be treated.