Cylinders

—The compre ion between cylinders now effects, in a few seconds, that condensation and distribution of the fibres, which 40 years ago, could not be accomplished till after many heats in the furnace, and many blows of the hammer. The cylinders may be distinguished into two kinds; 1. those which serve to draw out the ball, called puddling rolls , or roughing rolls, and which are, in fact, reducing cylinders; 2. the cylinders of extension, called rollers , for drawing into bars the ma ive iron after it has received a welding, to make it more malleable. This second kind of cylinders is subdivided into several varieties, according to the patterns of bar iron that are required. These may vary from 2 inches square to le than one-sixth of an inch. Beneath the cylinders there is usually formed an oblong fo e, into which the scoriæ and the scales fall when the iron is compre ed. The sides of this fo e, constructed of stone, are founded on a body of solid masonry, capable of supporting the enormous load of the cylinders. Beams of wood form in some measure the sides of this pit, to which cylinders may be made fast, by securing them with screws and bolts. Ma ive bars of cast iron are found, however, to answer still better, not only because the uprights and bearers may be more solidly fixed to them, but because the basement of heavy metal is more difficult to shatter or displace, an accident which happens frequently to the wooden beams. A rill of water is supplied by a pipe to each pair of cylinders, to hinder them from getting hot; as also to prevent the hot iron from adhering to the cylinder, by cooling its surface, and perhaps producing on it a slight degree of oxidize ment. The shafts are one foot in diameter for the hammer and the roughing rolls; and six inches where they communicate motion to the cylinders destined to draw the iron into bars. The roughing rolls are employed either to work out the lump or ball immediately after it leaves the puddling furnace, as in the Welsh forges, or only to draw out the piece, after it has been shaped under the hammer, as is practised in most of the Staff ords hire establishments. These roughing cylinders are generally 7 feet long, including the trunnions, or 5 feet between the bearers, and 18 inches diameter; and weigh in the whole from 4 to 4 1 ⁄ 2 tons. They contain from 5 to 7 grooves, commonly of an elliptical form, one smaller than another in regular progre ion, as is seen in fig. 597. The small axis of each ellipse, as formed by the union of the upper and under grooves, is always placed in the vertical direction, and is equal to the great axis, or horizontal axis of the succeeding groove; so that in transferring the bar from one groove to another, it must receive a quarter of a revolution, whereby the iron gets elongated in every direction. Sometimes the roughing rolls serve as preparatory cylinders, in which case they bear towards one extremity rectangular grooves, as the figure exhibits. Several of these large grooves are bestudded with small asperities analogous to the teeth of files, for biting the lump of iron, and preventing its sliding. On a level with the under side of the grooves of the lower cylinder, there is a plate of cast iron with notches in its edge adapted to the grooves. This piece called the apron, rests on iron rods, and serves to support the balls and bars exposed to the action of the rollers, and to receive the fragments of ill-welded metal, which fall off during the drawing. The housing frames in which the rollers are supported and revolve, are made of great strength. Their height is 5 feet; their thickne is 1 foot in the side perpendicular to the axis of the cylinders, and 10 inches in the other. Each pair of bearers is connected at their upper ends by two iron rods, on which the workmen rest their tongs or pinchers for pa ing the lump or bar from one side of the cylinders to the other. The cods or bushes are each composed of two pieces; the one of hard bra , which presents a cylindrical notch, is framed into the other which is made of cast iron, as is clearly seen in fig. 597. The iron bar delivered from the square grooves, is cut by the shears into short lengths, which are collected in a bundle in order to be welded together. When this bundle of bars has become hot enough in the furnace, it is conveyed to the rollers; which differ in their arrangement according as they are meant to draw iron from a large or small piece. The first, fig. 597. , po e both elliptical and rectangular grooves; are 1 foot in diameter and 3 feet long between the bearers. The bar is not finished under these cylinders, but is transferred to another pair, whose grooves have the dimensions proper for the bar, with a round, triangular, rectangular, or fillet form. The triangular grooves made use of for square iron, have for their profile, an isosceles triangle slightly obtuse, so that the space left by the two grooves together may be a rhombus, differing little from a square, and whose smaller diagonal is vertical. When the bar is to be pa ed succe ively through several grooves of this kind, the larger or horizontal diagonal of each following groove is made equal to the smaller or upright of the preceding one, whereby the iron must be turned one fourth round at each succe ive draught, and thus receive pre ure in opposite directions. Indeed the bar is often turned in succe ion through the triangular and rectangular grooves, that its fibres may be more accurately worked together. The decrement in the capacity of the grooves follows the proportion of 15 to 11. When it is intended to reduce the iron to a small rod, the cylinders have such a diameter, that three may be set in the same housing frame. The lower and middle cylinders are employed as roughing rollers, while the upper and middle ones are made to draw out the rod. When a rod or bar is to be drawn with a channel or gutter in its face, the grooves of the rollers are suitably formed. IMG:4147767755307473660_illo0706b.png:Rollers To draw out square rods of a very small size, as nail-rods, a system of small rollers is employed, called slitters . Their ridges are sharp-edged, and enter into the opposite grooves 2 1 ⁄ 2 inches deep; so that the flat bar in pa ing between such rollers is instantaneously divided into several slips. For this purpose the rollers represented in fig. 598. may be put on and removed from the shaft at pleasure. The velocity of the cylinders varies with their dimensions. In one work, cylinders for drawing out iron of from one-third to two-thirds of an inch thick, make 140 revolutions per minute; while those for iron of from two-thirds of an inch to 3 inches, make only 65. In another work, the cylinders for two inch iron, make 95 revolutions per minute; those for iron from two-thirds of an inch to an inch and a third, make 128; and those for bars from one-third to two-thirds of an inch, 150. The roughing rollers move with only one-third the velocity of the drawing cylinders. The shingling and plate-rolling mill is represented in fig. 597. The shingling mill, for converting the blooms from the balling furnace into bars, consists of two sets of grooved cylinders, the first being called puddling rolls or roughing rolls ; the second are for reducing or drawing the iron into mill-bars, and are called simply rolls . IMG:4147767755307473660_illo0706a.png:Rollers Fig. 597 enlarged (186 kB) a , a , a , a , are the powerful uprights or standards called housing frames , of cast iron, in which the gudgeons of the rolls are set to revolve; b , b , b , b , are bolt rods for binding these frames together at top and bottom; c , are the roughing rolls, having each a series of triangular grooves, such that between those of the upper and under cylinder, rectangular concavities are formed in the circumference with slightly sloping sides. The end groove to the right of c , should be channelled like a rough file, in order to take the better hold of the blooms, or to bite the metal as the workmen say; and give it the preparatory elongation for entering into and pa ing through the remaining grooves till it comes to the square ones, where it becomes a mill-bar. d , d , are the smooth cylinders, hardened upon the surface, or chilled as it is called, by being cast in iron moulds, for rolling iron into plates or hoops. e , e , e , e , are strong screws with rectangular threads, which work by means of a wrench or key, into the nuts e′ e′ e′ e′ , fixed in the standards; they serve to regulate the height of the plummer blocks or bearers of the gudgeons, and thereby the distance between the upper and under cylinders. f is a junction shaft; g , g , g , are solid coupling boxes, which embrace the two separate ends of the shafts, and make them turn together. h , h , are junction pinions, whereby motion is communicated from the driving shaft f , through the under pinion to the upper one, and thus to both upper and under rolls at once. i , i , are the pinion standards in which their shafts run; they are smaller than the uprights of the rolls. k , k , are screws for fastening the head pieces l to the top of the pinion standards. All the standards are provided with sole plates m , whereby they are screwed to the foundation beams, n , of wood or preferably iron, as shown by dotted lines; o o are the binding screw bolts. Each pair of rolls at work is kept cool by a small stream of water let down upon it from a pipe and stop-cock. In the cylinder drawing, the workman who holds the ball in tongs, pa es it into the first of the elliptical grooves; and a second workman on the other side of the cylinders, receives this lump, and hands it over to the first, who re-pa es it between the rollers, after bringing them somewhat closer to each other, by giving a turn to the adjusting pre ure screws. After the lump has pa ed five or six times through the same groove, it has got an elliptical form, and is called in England a bloom . It is next pa ed through a second groove of le size, which stretches the iron bar. In this state it is subjected to a second pair of cylinders, by which the iron is drawn into flat bars, 4 inches broad and half an inch thick. Fragments of the ball or bloom fall round about the cylinders; which are afterwards added to the puddling charge. In a minute and a half, the rude lump is transformed into bars, with a neatne and rapidity which the inexperienced eye can hardly follow. A steam engine of thirty-horse power can rough down in a week, 200 tons of coarse iron. This iron called mill-bar iron, is however of too inferior a quality to be employed in any machinery; and it is subjected to another operation, which consists in welding several pieces together, and working them into a ma of the desired quality. The iron bars while still hot, are cut by the shears into a length proportional to the size of iron bar that is wanted; and four rows of these are usually laid over each other into a heap or pile, which is placed in the re-heating furnace above described, and exposed to a free circulation of heat; one pile being set cro wise over another. In a half or three quarters of an hour, the iron is hot enough, and the pieces now sticking together, are carried in succe ive piles to the bar-drawing cylinders, to be converted into strong bars, which are reckoned of middle quality. When a very tough iron is wanted, as for anchors, another welding and rolling must be given. In the re-heating ovens, the lo is from 8 to 10 per cent. on the large bar iron, and from 10 to 12 in smaller work. A ton of iron consumes in this proce , about 150 lbs. of coals. It is thought by many that a purer iron is obtained by subjecting the balls as they come out of the puddling furnace, to the action of the hammer at first, than to the roughing rollers; and that by the latter proce vitrified specks remain in the metal, which the hammer expels. Hence, in some works, the balls are first worked under the forge-hammer; and these stampings being afterwards heated in the form of pies or cakes piled over each other, are pa ed through the roughing rollers. Having given ample details concerning the manufacturing proce es used in England for making cast iron, it may be proper to subjoin a few observations upon its chemical constitution. It has been generally believed and taught that the dark gray cast iron, No. 1. or No. 2., contains more carbon than the white cast iron; and that the superior quality of the former in tenacity and softne , is to be ascribed to that exce . But the distinguished German metallurgist, M. Karsten, in his instructive volume, “Handbuch der Eisenhüttenkunde,” or manual of the art of smelting iron ores, has proved, on the contrary, that the white cast iron contains most charcoal; that this substance exists in it in a state of combination with the whole body of the iron; that the foliated or lamellar white cast iron contains as much carbon as iron can absorb in the liquid state; and that this constitutes a compound of 4 atoms of iron combined with 1 of charcoal, or 112 + 6; or 5 1 ⁄ 3 per cent.; whereas the dark gray cast iron contains generally from 3 to 4 per cent., in the state of plumbago merely dispersed through the metal. He has further confirmed his opinion, by causing the white variety to pa into the gray, and reciprocally. Thus, dark gray cast metal melted and suddenly cooled, gives a silvery white metal, hard and brittle. On the other hand, when the white cast iron is cooled very slowly after fusion, the condition of the carbon in it changes, and a dark gray cast iron is obtained. These phenomena shew that the graphite or plumbago, which requires a high temperature for its formation, cannot be produced but by a slow cooling, which allows the carbon to agglomerate itself in the iron in the state of graphite; while under a rapid congelation, the carbon remains di olved in the ma , and produces a white metal. Hence we may understand how each succe ive fusion of dark gray iron hardens and whitens it, though in contact with coke, by completing that chemical di olution of the carbon on which the white state depends. In the manufacture of the blackest No. 1. cast iron, it sometimes happens that a considerable quantity of a glistening carburet of iron appears, floating on the top of the metal as it is run out into the sand-moulds. This substance is called kish by the English workmen; and it affords a sure test of the good state of the furnace and quality of the iron. The most remarkable fact relative to the smelting of cast iron, is the difference of product between the workings of the summer and the winter season, though all the materials and machinery be the same. In fact, no cold-blast furnace will carry so great a burden in summer as in winter, that is, afford so great a product of metal, or bear so great a charge of ore with the same quantity of coke. This difference is undoubtedly due to the dilated and humid state of the atmosphere in the warm season. A very competent judge of this matter, states the diminution in summer at from one-fifth to one-seventh, independently of deterioration of quality. Some of the foreign irons, particularly certain Swedish and Ru ian bars, are imported into Great Britain in large quantities, and at prices much greater than those of the English bars, and therefore the modes of manufacturing such excellent metal deserve examination. All the best English cast steel, indeed, is made from the hoop L, iron from Dannemora, in Sweden. The proce es pursued in the smelting works of the Continent have frequently in view to obtain from the ore malleable iron directly, in a pure or nearly pure state. The furnaces used for this purpose are of two kinds, called in French, 1. Feux de Loupes , or Forges Cat a lanes ; and 2. Fourneaux à pièce , or Forges Allemandes . IMG:4147767755307473660_illo0708.png:Catalan or French hearth In the Catalan, or French method, the ore previously roasted in a kiln is afterwards strongly torrefied in the forge before the smelting begins; operations which follow in immediate succe ion. Ores treated in this way should be very fusible and very rich; such as black oxide of iron, hematites, and certain spathose iron ores. From 100 parts of ore, 50 of metallic iron have been procured, but the average product is 35. The furnaces employed are rectangular hearths, figs. 599. and 600. , the water-blowing machine being employed to give the blast. See Metallurgy . There are three varieties of this forge; the Catalan, the Navarrese, and the Biscayan. The dimensions of the first, the one most generally employed, are as follows: 21 inches long, in the direction p f , fig. 600. ; 18 1 ⁄ 2 broad, at the bottom of the hearth or creuset , in the line A B ; and 17 inches deep, fig. 599. The tuyère, q p , is placed 9 1 ⁄ 2 inches above the bottom, so that its axis is directed towards the opposite side, about 2 inches above the bottom. But it must be movable, as its inclination needs to be changed, according to the stage of the operation, or the quantity of the ores. It is often raised or lowered with pellets of clay; and even with a graduated circle, for the workmen make a great mystery of this matter. The hearth is lined with a layer of brasque (loam and charcoal dust worked together), and the ore after being roasted is sifted; the small powder being set aside to be used in the course of the operation. The ore is piled up on the side opposite to the blast in a sharp saddle ridge, and it occupies one-third of the furnace. In the remaining space of two-thirds, the charcoal is put. To solidify the small ore on the hearth, it is covered with moist cinders mixed with clay. The fire is urged with moderation during the first two hours, the workman being continually employed in pre ing down more charcoal as the former supply burns away, so as to keep the space full, and prevent the ore from crumbling down. By a blast so tempered at the beginning, the ore gets well calcined, and partially reduced in the way of cementation. But after two hours, the full force of the air is given; at which period the fusion ought to commence. It is easy to see whether the torrefaction be sufficiently advanced, by the aspect of the flame, as well as of the ore, which becomes spongy or cavernous; and the workman now completes the fusion, by detaching the pieces of ore from the bottom, and placing them in front of the tuyère. When the fine siftings are afterwards thrown upon the top, they must be watered, to prevent their being blown away, and to keep them evenly spread over the whole surface of the light fuel. They increase the quantity of the products, and give a proper fusibility to the scoriæ. When the scoriæ are viscid, the quantity of siftings must be diminished; but if thin, they must be increased. The exce of slag is allowed to run off by the chio or flo hole. The proce lasts from five to six hours, after which the pasty ma is taken out, and placed under a hammer to be cut into lumps, which are afterwards forged into bars. Each ma presents a mixed variety of iron and steel; in proportions which may be modified at pleasure; for by using much of the siftings, and making the tuyère dip towards the sole of the hearth, iron is the chief product; but if the operation be conducted slowly, with a small quantity of siftings, and an upraised tuyère, the quantity of steel is more considerable. This primitive proce is favourably spoken of by M. Brongniart. The weight of the lump of metal varies from 200 to 400 pounds. As the consumption of charcoal is very great, amounting in the Palatinate or Rheinkreis to seven times the weight of iron obtained, though in the Pyrenees it is only thrice, the Catalan forge can be profitably employed only where wood is exceedingly cheap and abundant. The Fourneaux à pièce of the French, or Stuck-ofen of the Germans, resembles fig. 313. , ( Copper ); the tuyère (not shown there) having a dip towards the bottom of the hearth, where the smelted matter collects. When the operation is finished, that is at least once in every 24 hours, one of the sides of the hearth must be demolished, to take out the pasty ma of iron, more or le pure. This furnace holds a middle place in the treatment of iron, between the Catalan forge and the cast-iron flo -ofen , or high-blast furnaces. The stuck-ofen are from 10 to 15 feet high, and about 3 feet in diameter at the hearth. Most usually there is only one aperture for the tuyère and for working; with a small one for the escape of the slag; on which account, the bellows are removed to make way for the lifting out of the lump of metal, which is done through an opening left on a level with the sole, temporarily closed with bricks and potters’ clay, while the furnace is in action. This outlet being closed, and the furnace filled with charcoal, fire is kindled at the bottom. Whenever the whole is in combustion, the roasted ore is introduced at the top in alternate charges with charcoal, till the proper quantity has been introduced. The ore falls down; and whenever it comes opposite to the tuyère the slag begins to flow, and the iron drops down and collects at the bottom of the hearth into the ma or stuck ; and in proportion as this ma increases, the flo -hole for the slag and the tuyère is raised higher. When the quantity of iron accumulated in the hearth is judged to be sufficient, the bellows are stopped, the scoriæ are raked off, the little brick wall is taken down, and the ma of iron is removed by rakes and tongs. This ma is then flattened under the hammer, into a cake from 3 to 4 inches thick, and is cut into two lumps, which are submitted to a new operation; where it is treated in a peculiar refinery, lined with charcoal brasque , and exposed to a nearly horizontal blast. The above ma seized in the jaws of powerful tongs, is heated before the tuyère; a portion of the metal flows down to the bottom of the hearth, loses its carbon in a bath of rich slags or fused oxides, and forms thereby a ma of iron thoroughly refined. The portion that remains in the tongs furnishes steel, which is drawn out into bars. This proce is employed in Carniola for smelting a granular oxide of iron. The ma or stuck amounts to from 15 to 20 hundred weight, after each operation of 24 hours. Eight strong men are required to lift it out, and to carry it under a large hammer, where it is cut into pieces of about 1 cwt. each. These are afterwards refined, and drawn into bars as above described. These furnaces are now almost generally abandoned on the Continent, in favour of charcoal high or blast furnaces . Fig. 313. represents a schachtofen , (but without the tuyère, which may be supposed to be in the usual place), and is, like all the continental Hauts Fourneaux , remarkable for the exce ive thickne of its masonry. The charge is put in at the throat, near the summit of the octagonal or square concavity, for they are made of both forms. At the bottom of the hearth there is a dam-stone with its plate, for permitting the overflow of the slag, while it confines the subjacent fluid metal; as well as a tymp-stone with its plate, which forms the key to the front of the hearth; the boshes are a wide funnel, almost flat, to obstruct the easy descent of the charges, whereby the smelting with charcoal would proceed too rapidly. The bottom of the hearth is constructed of two large stones, and the hinder part of one great stone, called in German rückstein (back stone), which the French have corrupted into rustine . In other countries of the Continent, the boshes are frequently a good deal more tapered downwards, and the hearth is larger than here represented. The refractory nature of the Hartz iron ores is the reason a igned for this peculiarity. In Sweden there are blast-furnaces, schachtofen , 35 feet in height, measured from the boshes above the line of the hearth, or creuset . Their cavity has the form of an elongated ellipse, whose small diameter is 8 feet acro , at a height of 14 feet above the bottom of the hearth; hence, at this part, the interior space constitutes a belly corresponding with the upper part of the boshes. In other respects the details of the construction of the Swedish furnaces resemble the one figured above. Marcher relates that a furnace of that kind whose height was only 30 feet, in which brown hydrate of iron ( hematite ) was smelted, yielded 47 per cent. in cast iron, at the rate of 5 hundred weight a day, or 36 hundred weight one week after another; and that in the production of 100 pounds of cast iron, 130 pounds of charcoal were consumed. That furnace was worked with forge bellows, mounted with leather. The decarburation of cast iron is merely a restoration of the carbon to the surface, in tracing inversely the same progre ive steps as had carried it into the interior during the smelting of the ore. The oxygen of the air, acting first at the surface of the cast metal, upon the carbon which it finds there, burns it: fresh charcoal, oozing from the interior, comes then to occupy the place of what had been di ipated; till, finally, the whole carbon is transferred from the centre to the surface, and is there converted into either carbonic acid gas or oxide of carbon; for no direct experiment has hitherto proved which of these is the precise product of this combustion. This diffusibility of carbon through the whole ma of iron constitutes a movement by means of which cast iron may be refined even without undergoing fusion, as is proved by a multitude of phenomena. Every workman has observed that steel loses a portion of its steely properties every time it is heated in contact with air. On the above principle, cast iron may be refined at one operation. Three kinds of iron are susceptible of this continuous proce :—1. The speckled cast-iron, which contains such a proportion of oxygen and carbon as with the oxygen of the air and the carbon of the fuel may produce sufficient and complete saturation, but nothing in exce . 2. The dark gray cast-iron. 3. The white cast-iron. The nature of the crude metal requires variations both in the form of the furnaces, and in the manipulations. Indeed malleable iron may be obtained directly from the ores by one fusion. This mode of working is practised in the Pyrenees to a considerable extent. All the ores of iron are not adapted for this operation. Those in which the metallic oxide is mixed with much earthy matter, do not answer well; but those composed of the pure black oxide, red oxide, and carbonate, succeed much better. To extract the metal from such ores, it is sufficient to expose them to a high temperature, in contact either with charcoal, or with carbonaceous gases; the metallic oxide is speedily reduced. But when several earths are present, these tend continually, during the vitrification which they suffer, to retain in their vitreous ma the unreduced oxide of iron. Were such earthy ores, as our ironstones, to be put into the low furnaces called Catalan , through which the charges pa with great rapidity, and in which the contact with the fuel is merely momentary, there would be found in the crucible or hearth merely a rich metallic gla , instead of a lump of metal. In smelting and refining by a continuous operation, three different stages may be distinguished:—1. The roasting of the ore to expel the sulphur, which would be le easily separated afterwards. The roasting di ipates likewise the water, the carbonic acid, and any other volatile substances which the minerals may contain. 2. The deoxidize ment and reduction to metal by exposure to charcoal or carburetted vapours. 3. The melting, agglutination, and refining of the metal to fit it for the heavy hammers where it gets nerve. There are several forges in which these three operations seem to be confounded into a single one, because, although still succe ive, they are practised at one single heating without interruption. In other forges, the proce es are performed separately, or an interval elapses between each stage of the work. Three systems of this kind are known to exist:—1. The Corsican method; 2. The Catalan with wood charcoal; and 3. The Catalan with coke. The furnaces of Corsica are a kind of semicircular basins, 18 inches in diameter, and 6 inches deep. These are excavated in an area, or a small elevation of masonry, 8 or 10 feet long by 5 or 6 broad, and covered in with a chimney. This area is quite similar to that of the ordinary hearths of our blast-furnaces. The tuyère stands 5 or 6 inches above the basin, and has a slight inclination downwards. In Corsica, and the whole portion of Italy adjoining the Mediterranean shores, the iron ore is an oxide similar to the specular ore of the Isle of Elba. This ore contains a little water, some carbonic acid, occasionally pyrites, but in small quantity. Before deoxidizing the ore, it is requisite to expel the water and carbonic acid combined with the oxide, as well as the sulphur of the pyrites. The operations of roasting, reduction, fusion, and agglutination are executed in the same furnace. These are indeed divided into two stages, but the one is a continuation of the other. In the first, the two primary operations are performed at once;—the reduction of a portion of the roasted ore is begun at the same time that a portion of the raw ore is roasted: these two substances are afterwards separated. In the second stage, the deoxidize ment of the metal is continued, which had begun in the preceding stage; it is then melted and agglutinated, so as to form a ball to be submitted to the forge-hammer. The roasted pieces are broken down to the size of nuts, to make the reduction of the metal easier. In executing the first step, the basin and area of the furnace must be lined with a brasque of charcoal dust, 3, 4, or even 5 inches thick: over this brasque a mound is raised with lumps of charcoal, very hard, and 4 or 5 inches high. A semi-circle is formed round the tuyère, the inner radius of which is 5 or 6 inches. This ma of charcoal is next surrounded with another pile of the roasted and broken ores, which must be covered with charcoal dust. The whole is sustained with large blocks of the raw ore, which form externally a third wall. These three piles of charcoal, with roasted and unroasted ore, are raised in three succe ive beds, each 7 inches thick: they are separated from each other by a layer of charcoal dust of about an inch, which makes the whole 24 inches high. This is afterwards covered over with a thick coat of pounded charcoal. The blocks of raw ore which compose the outward wall form a slope; the larger and stronger pieces are at the bottom, and the smaller in the upper part. The large blocks are sunk very firmly into the charcoal dust, to enable them better to resist the pre ure from within. On the bottom of the semicircular well formed within the charcoal lumps, kindled pieces are thrown, and over these, pieces of black charcoal; after which the blast of a water-blowing machine ( trompe ) is given. The fire is kept up by constantly throwing charcoal into the central well. At the beginning of the operation it is thrust down with wooden rods, lest it should affect the building; but when the heat becomes too intense for the workmen to come so near the hearth, a long iron rake is employed for the purpose. At the end of about 3 hours, the two proce es of roasting and reduction are commonly finished: then the raw ore no longer exhales any fumes, and the roasted ore, being softened, unites into lumps more or le coherent. The workman now removes the blocks of roasted ore which form the outer casing, rolls them to the spot where they are to be broken into small pieces, and pulls down the brasque (small charcoal) which surrounds the ma of reduced ore. The second operation is executed by cleaning the basin, removing the slags, covering the basin anew with 2 or 3 brasques, (coats of pounded charcoal), and piling up to the right and the left, two heaps of charcoal dust. Into the interval between these conical piles two or three baskets of charcoal are cast, and on its top some cakes of the reduced crude metal being laid, the blast is resumed. The cakes, as they heat, undergo a sort of liquation, or sweating, by the action of the earthy gla es on the unreduced black oxide present. Very fusible slags flow down through the ma ; and the iron, reduced and melted, pa es finally through the coals, and falls into the slag basin below. To the first parcel of cakes, others are added in succe ion. In proportion as the slags proceeding from these run down, and the melted iron falls to the bottom, the thin slag is run off by an upper overflow or chio hole, and the reduced iron kept by the heat in the pasty condition, remains in the basin: all its parts get agglutinated, forming a soft ma , which is removed by means of a hooked pole in order to be forged. Each lump or bloom of malleable iron requires 3 hours and a half for its production. The iron obtained by this proce is in general soft, very malleable, and but little steely. In Corsica four workmen are employed at one forge. The produce of their labour is only about 4 cwt. of iron from 10 cwt. of ore and 20 of charcoal, mingled with wood of beech and chestnut. Though their ore contains on an average 65 per cent. of iron, only about 40 parts are extracted; evincing a prodigious waste, which remains in the slags. The difference between the Corsican and the Catalonian methods consists in the latter roasting the ore at a distinct operation, and employing a second one in the reduction, agglutination, and refining of the metal. In the Catalonian forges, 100 pounds of iron are obtained from 300 pounds of ore and 310 pounds of charcoal; being a produce of only 33 per cent. It may be concluded that there is a notable lo , since the sparry iron ores, which are those principally smelted, contain on an average from 54 to 56 per cent. of iron. The same ores smelted in the ordinary blast furnace produce about 45 per cent. of cast iron. On the Continent, iron is frequently refined from the cast metal of the blast furnaces by three operations, in three different ways. In one, the pig being melted, with aspersion of water, a cake is obtained, which is again melted in order to form a second cake. This being treated in the refinery fire, is then worked into a bloom . In another system, the pig iron is melted and cast into plates: these are melted anew in order to obtain crude balls, which are finally worked into blooms. In a third mode of manufacture, the pig-iron is melted and cast into plates, which are roasted, and then strongly heated, to form a bloom. The French fusible ores, such as the silicates of iron, are very apt to smelt into white cast iron. An exce of fluxes, light charcoals, too strong a blast, produce the same results. A surcharge of ores which deranges the furnace and affords impure slags mixed with much iron, too rapid a slope in the boshes, too low a degree of heat, and too great condensation of the materials in the upper part of the furnace; all tend also to produce a white cast iron. In its state of perfection, white cast iron has a silver colour, and a bright metallic lustre. It is employed frequently in Germany for the manufacture of steel, and is then called steel flo , or lamellar flo , a title which it still retains, though it be hardly silver white, and have ceased to be foliated. When its colour takes a bluish-gray tinge, and its fracture appears striated or splintery, or when it exhibits gray spots, it is then styled flower flo . In a third species of white cast iron we observe still much lustre, but its colour verges upon gray, and its texture is variable. Its fracture has been sometimes compared to that of a broken cheese. This variety occurs very frequently. It is a white cast iron, made by a surcharge of ore in the furnace. If the white colour becomes le clear and turns bluish, if its fracture be contorted, and contains a great many empty spaces or air-cells, the metal takes the name of cavernous-flo , or tender-flo . The whitest metal cannot be employed for casting. When the white is mixed with the gray cast iron, it becomes riband or trout cast iron. IMG:4147767755307473660_illo0712.png:German refining forge