causes it to give way and let the ore fall down to the hearth before it is sufficiently cemented by contact with the carbonaceous matter. THE BLAST FURNACE. We now come to describe this principal agent in the iron manufacture. In plate 89, which contains a plan and elevation of a furnace, with its appurtenances, A A represents what is called the stack of the furnace, of a pyramidal figure, 30 feet square at the base, and 40 feet in height, B B is the casting house, D is the house for the steam engine which gives motion to the blowing engine, to supply the furnace with air, a is its chimney, b the boiler with the fire place beneath it: the plan shows two such boilers, either of which will supply the engine when the other is out of repair. The two dark circles e e in the plane are holes which convey the coals down to the arch before the fire place of each boiler; f is the steam pipe leading to the cylinder; h is the great lever or bean of the engine, alternating upon its centre and communicating the motion of the piston to the blast cylinder, E, which is a large lifting pump, as shown in fig. 3. of plate 2. The engine is of the atmospheric principle, which, with its construction and operation are detailed under the article STEAM ENGINE; it is sufficient here to say that the alternate motion of the piston of the blowing cylinder, forces its contents of air at each stroke through the pipe i, into the regulating receiver F, which is an immense chest formed of cast iron plates, open at the lower side and inverted in a reservoir of water about 12 feet in depth. The air is conveyed from the regulator to the furnace by pipes k k proceeding from each end of the chest to the furnace. Those furnaces which possess the command of a waterfall are blown by an engine similar to that described under our article BLOWING ENGINE, either with or without the addition of a regulator. The blowing cylinder E, is only of single power, that is, it throws out air only on the ascent of its piston; and it is the office of the regulator F to receive this air at intervals and deliver it regularly into the furnace; and at every stroke of the engine, a quantity of water is displaced from the reservoir, by the engine throwing more air into it, than the two nose pipes at the ends of the pipes kk will convey away in the same time; it therefore distends the capacity of the receiver by expelling a portion of the water, and on the descent of the piston, when the engine supplies no air, the return of the water into the receiver continues the blast until the cylinder resumes its office. The superficial area of the receiver must be very great, so that the introduction of a cylinder of air will not cause such a descent of the water as to be sensible, in the difference of pressure by the surrounding water. The internal dimensions of the receiver before us are 30 feet long, eight feet broad, and 10 feet deep. It is formed of cast iron plates screwed together, and loaded with an immense weight of masonry to keep it down steadily in its place. The external cistern is built of masonry or brickwork, lined in such a manner as to avoid all danger of the escape of the water. Plate 90 will explain the internal construction of the furnace. The mass of stone work A A called the stack, is lined with two thicknesses BB of brick or stone, which will withstand the continued action of an intense heat; between the two is a layer of sand, represented by the dark lines in the figures. The cone B B is termed the funnel of the furnace, its base abuts upon an inverted frustum D D, more obtuse, called the boshes. Beneath this the diameter of the funnel is much diminished, being brought to a square figure; and it is at this part G called the hearth, where the blast is introduced by the two pipes kk. The lower part of the stack is perforated on three sides with arches; the two which are opposite are called tuire arches (from tuyau, pipe), E E, in the section 2. Their use is to expose the masonry of the hearth that the tuires (i. e. the apertures through which the blow pipes are entered) may be accessible. The other arch F, section 1, is called the tymp arch from its leading to the tymp stone a, forming one side of the hearth, from the top to within about inches of the floor; it is made moveable, that it may be easily renewed when burnt; and to preserve it, if it should split by the intense heat, an iron, plate 6 and figure 4, is placed behind it, having an angle below to sustain the stone. Both are fastened into their places by wedging against the side walls of the hearth: the opening below the tymp is stopped by the dam stone d set up upon the floor of the hearth, at about 20 inches' distance from the tymp. 18 The ends of the pipes kk, coming from the regulator, are connected with the blow pipes m, by very strong leathern tubes, which are joined to the pipes by hoops n, adjustable by screws, so as to hold the leather tight round them. By means of these leathern pipes the blow pipe m can be directed to blow into the furnace, in any direction within the limits of the tuires, or aperture to receive the pipes which are made through the stone work and lined with fire clay the two small circles in the hearth of section 1, show the position of the two tuires, and that they do not blow opposite each other. The constructions of blast furnaces are as various as their dimensions. Our plate 90 represents that kind which is in most universal use in Derbyshire. A great number of new furnaces have been erected which possess evident advantages, but yet require the sanction of all-powerful custom to render their introduction general. Considerable allowance is on this score to be made to manufacturers on account of the heavy loss which would be sustained by the unsuccessful experiment of a new constructed furnace, and the comparative small advantage to be obtained from its perfect success. The internal figure of a blast furnace has great influence upon its operation, requiring to be varied, according to the nature of the fuel and ore it is to be charged with. The furnace is not merely to be considered as a hearth for the fusion of the matters introduced into it, but as an extensive laboratory for separating the metal from its earthy mixtures. When first introduced, the ore becomes gradually heated. As it descends in the furnace by the consumption of the fuel beneath, it is roasted, and, by contact of carbon supplied by the fuel, parts with its oxygen. This operation requires to be continued from 24 to 36 hours, more or less, as the ore employed is disposed to part with its oxygen. It is evident that the time any quantity of ore takes in passing down through the furnace, will be regulated by the proportions of its height and internal diameter. In a low and proportionally large furnace the materials will speedily arrive at the hearth, being little retarded by friction against the sides of the funnel, and having less space to pass through. Such was the form of the old charcoal furnaces, which required less time, from the greater quantity of carbon in the furnace. The deficiency of carbon in pit coal must be compensated by an additional period of cementation in the furпасе. The descent of the materials is retarded by diminishing the diameter and increasing the height. In the same manner the furnaces burning soft cokes require narrower furnaces, than for hard cokes which have a similar quality as to their carbonic contents. This is necessary, that the cokes may be more fitted to sustain the weight of water above them without being crushed: for hard cokes, but which are inferior in their carbon, a high furnace is adapted to produce a long continued cementation. Similar reasons apply to the different qualities of ore as well as coal : longer in passing through the furnace than others some requiring to be in proportion as they are disposed to part with their oxygen these various combinations render the proportions of the internal figure of an iron furnace so uncertain that no particular size can be mentioned as general. The furnace in the plate is 40 feet in height from the bottom of the earth to the top; while others we have seen are as much as 60 feet. Many furnaces have the side of the funnel B B curved instead of straight, with a view to obviate any danger of the materials sticking in the furnace; which would have bad effects by rendering the operation of the furnace uncertain; owing to the sudden descents which must frequently occur by introducing improperly cemented ore into the furnace. : The intense heat raised in the furnace generally destroys the lining in about a year: though some will last three years, and others not six months; according to the quality of the lining. When this happens, the furnace is burnt out, the stone work of the hearth and lining B B is removed, and new put in without deranging the masonry of the stack; the dam stone, in consequence of having the fluid metal constantly pended up against it, seldom lasts more than three months, and must be renewed without extinguishing the furnace; during the operation sand is rammed in under the tymp stone to keep in the heat, and the blast is stopped. The tymp is changed in the same manner when necessary. house BB is provided with a crane to raise large The casting work: its floor should be many feet deep, with casting sand; and it should contain a reverberating furnace, cupola, and all the apparatus described in our article FOUNDRY for casting the iron in its various articles. other works not possessing such advantages of ground, machinery is constructed to supersede manual labour altogether, in charging the furnace. In the elevation, Pl. 89, the dotted line KK repre. L L is the original level of the ground, where the sents the inclined plane of the furnace, and the lex works are constructed: these lines are represented shown by K K in the plan, when they would be as at right angles to their true position, which is hidden behind the furnace in the elevation. Operation of the Blast Furnace. The furnace is lighted by introducing wood a and the dam stone left out to cause a draft, wh the top, then a few cokes; the tuires are stopped 4. is then lighted and is suffered to burn a fortnight, is of course very great in a tall furnace. The wood the furnace becomes heated and gradually fe a few cokes being introduced once every day t four baskets equal to eight bushels of cokes, 12 stone The charging of the furnace now commences with flux; the dam stones are put in, and, eight or misc of 14lb. each of ore; and four of limestone for a days afterwards, during which interval 60 or 7 charges are introduced, the tuires are opened and the blast commenced; at first gently with a smil nose pipe, and afterwards with a larger, m precautions are necessary to preserve the mase the furnace acquires the proper heat. The ry of the furnace from cracking; which would otherwise happen by the unequal expansion of so large a mass, if the heat were urged too rapidly. Twelve hours after the blast begins, iren en be obtained from the furnace; and in the core of as many days, if the business is well conductei, the furnace arrives at its proper heat and st for working constantly, as long as the lining lasts. The regular routine charging every half hour with eight bushels of co takes plt. tions, according to the quality of the iron to le mixed with ore and limestone in different prajar. produced. now The ore and limestone when put into the is consumed, becoming heated; and the earben. furnace gradually descend as the matter bel which abounds in the furnace, enters into com pass off in the state of carbonic acid gas. A bination with the oxygen of the ore, and both carbon and the metal thus deprived of the cxynew combination now takes place between the the ore continues to descend and the heat ingen; the carbonization proceeds more rapidly as creases. This process is arrives about the top of the cokes, where the best continued until k becomes so intense, as to fuse both the iron and any of the impurities it contains: they now An immense mound of earth is raised up, to form drop down in a fluid state, and accumulate in an inclined plane from the ground to the top of the the bottom of the hearth, being kept in by the furnace, on which the fuel and materials are condam stone a from flowing out into the castingveyed to the top of the furnace. The scite of a house: while the matter remains here, the irra blast furnace is mostly upon the declivity of a hill, other melted matters form a liquid lava floating by its superior weight sinks to the bottom; the for the greater convenience of constructing the inclined plane. In many cases, where the inclination upon it, and rising up as the quantity increases, of the hill is considerable, it is practicable to make until it becomes high enough to flow over the the top of the furnace level with the coke-yard The metal also accumulates, and in twelve beurs dam stone upon the sand of the casting-house. where the fuel and ore are prepared for it. this case the steam engine house, and its boiler- The dam stone is not made long enough to th In after the commencement, is ready for casting. house, are carried up as high as the furnace, entirely the space in which it is placed, but and the bridge loft or road to the top of the furnace is constructed over the top of the build- of it and the side walls of the hearth: this aperabout three inches' space is left between ose erd ing. This arrangement saves ble expense in the formation of the mound. At when the metal is to be cast, and suffered to a very considerature is stopped with sand, which is removed |