Forge or bar iron is pig-iron freed from car bon and oxygen. The first operation for pro ducing this change is called refining, and is performed in small low furnaces, about three feet square at the base, having the bottom, or hearth, of fire-bricks, and the sides of cast iron, made hollow to allow a stream of water to pass constantly through, which prevents their being quickly burnt away; near the top are holes for the insertion of blast-pipes. The iron is kept in a state of fusion in the refinery for some time exposed to an intense heat pro duced by a strong blast, and is then run out into a flat mould twenty feet long by two wide, placed over a cistern of water, where it speedily cools into a bright brittle state.
The first process employed for making bars is called puddling, and is performed in a rever beratory or.puddling furnace. [FuRNAcE.] The quantity of refined metal put into this pud dling-furnace at each charge is from 31 to 4 cwt. In about half an hour from the charging of the furnace the metal begins to melt. The puddler then observes, through a small hole provided for that purpose and for the intro duction of his tools, the progress of the work. The business of the puddler is so to dispose of the pieces of metal, moving them by means of his tools, as to ensure an equable applica tion of heat to the mass. When the whole quantity is fully melted, the puddler stirs the metal about briskly, changing his tools contin ually, that they may not be melted. By means of this agitation the metal gives off an elastio fluid, and after a time becomes thick, and grows increasingly so, until it loses all fluidity and forms into lumps. The contents of the furnace are then divided into five or six por tions by the puddler, and each is made up by means of his tools into a spherical form. These balls are technically called blooms. Being taken from the puddling-furnace, they are subjected each to ten or twenty blows from a heavy hammer (called shingling), or to an intense pressure by a machine called a squeezer, which makes them more compact and gives them a shape more convenient for going through the rollers. These rollers consist of two cylinders working in contact, and having on their surfaces a series of grooves, varying in size. The iron is passed through all these grooves in succession, until it is reduced to the requisite width and thickness. It is thus con verted from a fusible, hard, and brittle sub stance, to a tough and elastic bar which is hardly fusible, and which, from its property of yielding and altering its form under the ham. mer, has acquired the name of malleable iron.
The bars, when they have been passed through these rollers, and while yet hot, are cut into convenient lengths and taken to the balling-furnace, the shape and construction of which resemble these of the puddling furnace. In this balling furnace the bars are piled evenly, so that one bar does not project beyond another. Several of these piles, each of which is composed of five or six bars, are placed at once in the furnace,and when sufficiently heated, so that they will weld together, the piles are taken out separately, and are passed again through rollers similar in construction to those described above, but differing from each other in the form of their orifices and grooves, so that either round or flat or square rods and hers may be produced at the pleasure of the maker, and these, when weighed and put up into bundles, are ready for sale.
The progress of the Iron Manufacture in this country has been astonishing. The quan tity of iron made in diftbrent years presents the following results : 1710 17,300 tons.
175Q 22,000 1788 .. l8,000 1796 .. 125,000 1806 250,000 1820 .. 400,000 1830 .. 677,417 1840 .. 1,396,400 1818 .. 1,098,568 The quantity of nearly two million tons in 1s48 was thus made up : England .. 735,800 tons.
Wales 722,800 Scotland .. 539,908 1,998,508 tons.
The near approach of Wales to England in produce is remarkable, and shows how rapidly the iron manufacture of South Wales must have been extending.
In 1700 each furnace throughout the king dom yielded an average produce of about 1000 tons of iron annually ; hu 1840 the average yield was about 6000 tons : so great have been the improvements in the manufacture: In 1848 the total number of furnaces, in and out of blast, was 623. The price of bar iron, at the close of ten successive years, was as fol lows :-1840, 81 ; '41, 61 ; 6 ; '43, £5 ; '44, .tai ; '45, .£10 ; '46, £81 ; '47, 91 ; '48, 51 ; '49, 51. Best iron, angle iron, rail iron, sheet iron, and hoop iron, all exceed the above prices by Is. to 40s. per ton. The highest price of pig iron for the last twenty years has been £61 per ton ; and the lowest about £2.
A few further details of the iron districts will be found under GLASGOW, MERTITYR, STAFFORDSHITSE, WALES, &c.
Our Exports of iron are very large. In 1849 the quantity of Bar, Pig, Bolt, Rod, Wire, Cast, and Wrought iron exported was 772,865 tons ; besides iron in the forms of steel, cut lery, hard ware and machinery, to the value of 4,077,1511. ; making altogether a value of about nine millions sterling.
The various manufactures in which iron or steel are employed to considerable extent are noticed. under their proper headings in this work ; such as CUTLERY, FILES, NAILS, NEED LES, Saws, &C. ; See also STEEL MANUFACTURE.
We may notice here the modern and very use ful form of galvanized tinned iron, as pre pared under the patent of Messrs. Morewood and Rogers. The sheets are rolled in the usual way, to any required degree of thinness ; some are kept in the original flat state ; while'others are corrugated, or brought to the form of alternate ridges and hollows. Both surfaces are covered with a layer of tin by the galvanic process, analogous to those noticed Tinder ELF CTRO-METALLURGY. This material, either in the flat or the corrugated form, is used for roofing, ships' bolts and sheathing, carriage roofs, tunnel linings, gutters, pipes, cisterns, chimney pots, cowls, baths, cans, buckets, coal-boxes, stove pipes, and numerous other articles. Temporary houses and stores, made of corrugated iron, are sent out to the colonies and California.
It is to be hoped, and reasonably expected, that every department of a manufacture on which so much of the prosperity of England depends, will be well represented at the ap proaching Exhibition. Nor is it less to be desired that foreign countries should shew their strength in the same direction.