Iron

At the time when foot-blasts were used for separating the metal, the art of casting iron was either altogether unknown, or in a state that it could not be prosecuted with advantage. In the reign of Elisabeth, blast furnaces were of a sufficient size to produce, with ores and the charcoal of wood, from two to three tons of pig-iron per day, or from fifteen to twenty tons per week. It was only, how ever, in the most favourable situations for obtaining water-power that such great products were obtained, and the greatest proportion of it was converted into bar-iron by means of the refinery fire ; but in many of the small works the iron was " matured," that is, made malleable, before it was drawn from the furnace. Wood, however, becoming scarce, or being engrossed by the great manufacturers, induced several enterprising individuals to attempt the substi tution of pit coal for making pig-iron. Mr. Simon Sturtevant, 1612, had a patent granted to him, for thirty-one years, for that purpose. By the terms of his patent he was bound topublish the nature and process of his invention, which he did, in a quarto book, entitled hfetallica ; this book, Mr. Gray says, does not contain aparticle of useful knowledge, but that it is an extremely curious specimen of the pedantry usual in James's reign. Sturtevant failed in executing his proposed plans, and was obliged, the following year, to render up his letters patent, or monopoly. John Ravenson, Esq. succeeded Sturtevant in 1813, had a patent granted to him, wrote his Look, entitled "A Treatise of !detainee, but not that which was published by Mr. Simon Sturtevant." Ravenson states, that at that time an iron work usually required from 10001. to 15001. to set it a-going, but that on his plan a capital of 1001. was fully adequate to commence a work. The furnace itself was to cost but 101. except the stones, such furnace being capable of producing a ton of sow iron from each ton of it coal. This man, however, failed in his attempts to prove the correctness of his statements, and resigned his patent. Several other unfortunate adventurers followed Ravenson in succession, who also obtained patents, failed in their undertakings, and resigned their privileges. It is a singular fact, that although pit coal was known long before this period, and great quantities of it were exported to Holland and the Low Countries, where it was used in the smith's forge, and in other manufactories that require a strong continued heat; yet in England the prejudice against its use in the manufacture of cast iron was eo inveterate, that when it was first proposed and attempted, every obstacle that could be devised was thrown in its way, and none of the adventurers succeeded, until the year 1619, when Dudley had a patent, and manufactured pig-iron in a blast furnace, but produced only three tons in a week. He became, however, the object of jealousy to the other manufacturers, who contrived to get his patent limited from thirty-one to fourteen years, and his devoted works were destroyed by a lawless mob, urged, it is supposed, by his rivals in business. Soon after this, Captain Buck, Major Wildman, and some others, constructed air furnaces in the forest of Dean, in which they placed large clay pots (similar to those used in glass-houses) for containing the requisite preparations of ore and charcoal, the flame of pit coal being employed for heating the furnaces; and it was expected, that by tapping the pots below, the separated material would flow out. But the heat was not sufficiently intense to produce an entire separation of the metal, the pots cracked, and the scheme was abandoned. At this time iron was advancing, in consequence of many of the iron works having stopped for want of fuel. To those manufacturers, therefore, who could still be furnished with a supply of wood, the manufacture was highly profitable, and they obstinately opposed any new attempt by which the price of iron might be diminished. It was not till impelled by necessity, arising from the rapid decline of the annual growth of timber, that pit coal became an object of universal estimation. In this feeling the Hon. Robert Boyle seems to have participated, for in his Usefulness of Natural Philosophy, published in 1663, he expresses a desire that some method could be found to make coke without the use of pots employed for that purpose, in order that it might be applied to the smelting of iron ores. Two years after this, Dudley (according to Mr. Gray) wrote his Metallum Mortis, in which he states, that his father and himself had smelted iron with coke in large quantity, but that Oliver Cromwell, and some favourites of his, wishing, on a renewal of the patent, to become partners, and other political circumstances, had ruined the establishment, which seems never to have been revived ; for even so late as the year 1747, Mr. Mason says, in the Philosophical Transactions, that several attempts have been made to melt iron ore with pit coal, but he thinks it had not then succeeded any where, as no account of its being practised had been published, but that Mr. Ford did, however, then make pig iron, brittle or tough, as he pleased, from iron and coal, both of which were procured on the same spot. The brittle or inferior quality of English bar iron, made from coke at this period, and the great expense of that which was made from charcoal, owing to the increasing scarcity of wood, was most likely the cause of the great decline in the home manufacture of iron which then took place ; recourse having been had to Sweden and Russia for a supply, the importation of which on a great scale at this time commenced. The home manufacture was, however, again renewed by the general introduction of the steam engine, which afforded the manufacturer the command of a power he had before no conception of. The small furnaces supplied with air from bellows worked by oxen, horses, or men, were given up; larger furnaces were introduced, and blowing machines, with an increase of the column of air for exciting a more vivid combustion. The steam engine was found particularly beneficial in those situations where there was an abun dance of minerals for making iron, but a deficiency of water to supply the power. Experience also soon taught the manufacturer, that the produce of his furnace could be increased by enlarging the diameter of his steam cylinder and rendering the vacuum therein more perfect. It was soon found, that by increasing these effects, a quantity of pig-iron could be produced from the coke of pit coal, which would be attended with an adequate profit. Owing to the small quantity of air necessary to ignite, and preserve the required heat in a charcoal furnace, the manufacturers very cautiously enlarged the dimensions of their blowing apparatus in applying it to coke ; consequently much of the advantage resulting from a great blast (which is now extended to about 4000 cubic feet of air per minute) was lost. These difficulties were, however, gradually surmounted, and it appears, that before the year 1760, the coke of pit coal was in general use for blast furnaces. The iron trade assumed new vigour, and made most rapid progress, as will appear from the following state ment of the total quantity of iron made in Great Britain between the years 1740 and 1827. Since the latter period, the manufacture and trade has been on the increase, notwithstanding the price has advanced.

In the year 1740, 17,000 tons were made from 59 furnaces.

„ 1788, 68,000 tons 121 „ „ 1796, 125,000 tons IP - „ „ 1806, 250,000 tons — „ „ 1820, 400,000 tons „ 1827, 690,000 tons 284 „ Of which latter quantity there were produced— By Staffordshire . . . . 216,000 tons from 95 furnaces. By Shropshire . . . 78,000 „ 31 „ By South Wales . . . 272,000 „ 90 „ By North Wales . . . 24,000 „ 12 „ By Yorkshire . . . . 43,000 „ 24 „ By Derbyshire . . . 20,500 „ 14 „ By Scotland 36,500 „ 18 „ Total . . . 690,000 „ 284 „

In the foregoing statement, several furnaces in Gloucestershire, Cheshire, and other places are omitted, which will render the produce in round numbers 700,000 tons. About three-tenths of this quantity are of a quality suitable to the foundry, which is all used in Great Britain and Ireland, with the exception of a small quantity exported to France and America. The other seven-tenth. are made into bars, rods, sheets, wire, &c., of which a large quantity is exported to all parts of the world. Having thus given a brief historical sketch of the rise and progress of this interesting and useful manufacture, we proceed to lay before our readers a concise account of the process by which iron is obtained from its ores, and brought into a crude or pure state, adapted to the wants of mechanics, or to the various uses to which it is applied.

Making of Coke.—The first operation is the preparation of the coal, to reduce it to the state of coke, which is accomplished either in kilns, or in the open air. The latter plan has been, and is still, the most extensively adopted; we shall therefore describe it the first. An oblong square hearth is prepared, by heating the earth to a firm flat surface, and paddling it over with clay. On this the pieces of coal are piled up, inclining toward one another ; and those of the lower strata are set upon their acutest angle, so as to touch the ground with the least surface possible. The piles are usually from 30 to 50 inches high, from 9 to 16 feet broad, and contain from 40 to 100 tons of coal. A number of vents are left, reaching from top to bottom, into which the burning fuel is thrown; and they are then immediately closed with small pieces of coal beaten bard in. Thus the kindled fire is forced to creep along the bottom, and when that of all the vents is united, it rises gradually, and bursts out on every side at once. If the coal contain pyrites, the combustion is allowed to continue a con siderable time after the disappearance of the smoke, to extricate the sulphur, part of which will be found in flowers on the surface. If it contain none, the fire is covered up soon after the smoke disappears, beginning at the bottom and proceeding gradually to the top. In 50, 60, or 70 hours, the fire is in general completely covered with ashes of char, formerly made, and in twelve or fourteen days the coke may be removed for use. In this way a ton of ordinary bituminous coal commonly produces from 700 to 1,100 lbs of coke.

Coke and Tar Works.—The annoyance attending this process by the evolution of the immense quantities of smoke from the ignited matter, besides the entire waste of the volatile products, induced Lord Dundonald, many years since, to carry into effect a plan for preventing the former, and saving the latter. One of these tar works, as they were called, was erected at Mr. Wilkinson's great works at Bradley, another at Tipton, and a third at the Level Colliery and iron works upon Dudley-wood. Being erected in the vicinity of large iron and coal works, the iron masters furnished the tar works with raw coal, and received in return the cokes produced by such coal, the proprietors being coin• pensated by the volatile products, viz. tar, pitch, varnish, and ammonia.

Coke Ki&e.—The last described process of making cokes, is now being superseded in many places, particularly in the neighbourhood of Sheffield, by the employment of kilns made of bricks, of a hemispherical form, about ten feet diameter at the base, and about two feet at the top, where a circular opening is left for the introduction of the coal. The manner of working these ovens is thus described by Mr. Parker :—" When these ovens are once heated, the work goes on night and day without interruption, and without any further expense of fuel. It is conducted thus : small refuse coal is thrown in at the circular opening at the top, sufficient to fill the oven up to the springing of the arch ; it is then levelled with an iron rake, and the doorway on the side built up with loose bricks. The heat acquired by the oven in the former operation is always sufficient of itself to light up the new charge, the combustion of which is accelerated by the atmospheric air that rushes in through the joints of the loose bricks in the doorway. In two or three hours the combustion gets to such a height, that they find it necessary to check the influx of the air; the door way is therefore now plastered up with a mixture of wet soil and sand, except the top row of bricks, which is left unplastered all night. Next morning, when the charge has been in twenty-four hours, this is completely closed also, but the chimney remains open till the flame is gone, which is generally quite of in twelve hours more. A few loOse stones are then laid over the aperture, and closely covered up with a thick bed of sand or earth. All connexion with the atmosphere is now cut off, and in this situation the whole remains for twelve hours to complete the operation. The doorway is then opened, and the cokes are raked into iron wheel barrows, to be carted away. The whole operation takes up forty-eight hours, and as soon as the cokes are removed, the ovens are again filled with coal for another burning. About two tons of coals areput in for each charge, and the cokes produced are ponderous, extremely hard, of a light grey colour, and shine with metallic lustre; they acquire in the furnaces an intense heat, and will sustain a great burthen of iron-stone and other materials." When coke is required to be more of the nature of charcoal, the process is conducted in a different manner. The small coal is thrown into a large receptacle, similar to a baker's oven, i previously brought to a red heat. Here the door is constantly open, and the heat of the oven is sufficient to dissipate all the bitumen of the coals, the disengagement of which is promoted by frequently stirring it with a long rake. The coke from the ovens, though made from the same kind of coal, is very different from that produced by the former operation, this being intensely black, very porous, and as light as pumice stone. Under the article Liaz-Boannto, a drawing and description of a patent oven for making coke is given, in which the latter operation is made subservient to the first. The mechanical arrangement and process therein exhibited, may be advantageously applied to the roasting of ores instead of lime, and the coke required for the smelting furnace might be made at the same time. As we have extended our observations on the making of coke from pit coal to a length which some of our readers may probably consider to be unsuited to its real importance, we would observe, in the language of Dr. Colquhoun, that the substance "has been the means of advancing the manufacture itself in this country, to an extent which is unparalleled in the history of any other country or nation. It has now been ascertained, by long experience, that there is no other fuel which is so well fitted at once to supply the heat of the furnace, and, at the same time, to endure the powerful blast which is incessantly forced upon it. It may now be said to be essential to our iron manufacture, which would, indeed, be almost annihilated were the supply of it withdrawn." Without it we should be compelled to lay under wood immense tracts of what are now fertile corn fields, in order to supply, at an enormous expense, a much more imperfect fuel for the furnace. But the treasure of it seems to be inexhaustible, and not less so the metal for which it is required, as will be seen upon reference to the article COAL, wherein we have given a section of Bradley mine, and the arrangement of the numerous distinct strata cut through to arrive at the coal, amongst which there occurs from thirty to forty feet thickness of iron-stone, before the principal bed of coal is arrived at.