398

MANUFACTURES.

fer;ile. The philosopher, while he studies the progressof the human understanding, and compares the fortuneand state of the different nations established on variousportions of the surface of the Globe, will remark, thattheir iron-Works seem, in some measure, to be propor-tioned to their intelligence, to the advancement of reasonamongst them, and the degree of perfection to which theArts nave arrived. When we consider it in this pointof view, as the agent by which men, in the variety ofits uses, and the numerous wants it supplies, acquire en-joyments which would be unknown to them if they didnot possess these products of their industry, iron mustsingularly contribute to extend their ideas, to multiplytheir knowledge, and to conduct their spirit towards thatperfectibility, which Nature has given no less as the cha-racter of the human species, than as the source of allthe advantages it can enjoy.”

Iron is a malleable and ductile metal, of a bluish-whitecolour, is susceptible of a very high polish, and ot thespecific gravity, variously stated, from 7.600 to 7.895.

General View of the Process of making Iron.

General (553.) There are several particulars connected with the

process conversion of iron ore to a metallic state, which require todescribed. t)e rather minute i y described; but we think that thesewill be better understood by readers unacquainted withthe subject, if we first, without- attending to minutiae,describe generally the several steps of the process. Wemay then return and point out those peculiarities whichrequire further illustration.

Roasting. The first step to be taken after the ore has been ob-tained, is to submit it to a considerable degree of heatin a kiln, in order to drive off' the water, carbonicacid, sulphur, and other ingredients which enter largelyinto the composition of the ore. This is technicallycalled roasting or calcining, and in the process a loss ofweight is sustained of from 20 to 30 per cent. Thekiln is fed at the top, as the roasted ore is removed fromthe bottom, after having sustained the requisite degreeof heat; and considerable skill is exercised in this firstprocess ; for i( there be too much heat the pieces of ore,or, as it is called in Wales , the mine , will melt and ad-here together; and if too little, they will contain a por-tion of water or sulphur, and are obliged to be thrownaside at the kiln as raw or green mine.imelting. The next step in the process is to convert the calcined oreor mine to its first metallic state. This is effected in theblast furnace, in which proper proportional quantities ofore and coke are employed, with some other substanceto act as a flux, the latter depending upon the nature ofthe ore ; particulars of which will be described as we pro-ceed. These materials are submitted to a strong blast, pro-duced by some one of the powerful blowing Machinesalready described. (Art. 383.) As this process proceeds,the metal falls in a fluid state to a part at the bottom of thefurnace called the hearth, which is of different dimensionsin different Works ; in some the quantity of fluid metalproduced every twelve hours amounts to from four tosix tons, and at these intervals it is generally run off',forming what is called pig iron.

Runningoff The method of running off may be thus described: athe metal, hole is already formed at the bottom of the hearth,which is stopped with a mixture of sand and clay duringthe smelting process ; but when ready, the hearth is tap-ped by opening this aperture, and the metal of courseissues. The stream of metal is received from this aper-

ture into a long channel formed in a sort of sand, and Mechaji^cafrom this principal channel, which is called the sow, ‘ uc e8il ,there proceed laterally a number of smaller channels, ' '*~' rcalled pigs, of the well-known shape of pig iron. Asthe fluid proceeds down the central channel, the work-man interrupts its progress every now and then by along piece of wood, in order to cause the metal to flowinto the lateral channels as it proceeds, as otherwise itwould not retain sufficient fluidity to flow into these, soas to form each completely ; but by stopping it as abovedescribed, the pigs are all perfectly formed in the orderin which the metal flows. As soon as the metal is wellset, the pigs are broken off from the central channel orsow, and the latter is also broken to pieces by the blowsof a large sledge hammer. The quantity of metal thusobtained, compared with the quantity of roasted oreemployed in its production, varies of course considerablywith different ores, but the product may, at a mean esti-mate, be stated to amount to about 40 per cent. Andwe have seen that in the roasting a loss of weight hasbeen sustained of from 20 to 30 per cent.; so that fromthe raw mine to the first state of pig iron, a loss is sus-tained of about 66 per cent., or, which is the same, it re-quires about three tons of raw mine to form one of pig iron.

The iron in this state of pigs is distinguished into sixdifferent kinds, depending on circumstances which willbe described further on: of these, the first three, viz. -numbers 1, 2, 3, are considered as foundery metal ; theycontain carbon in different degrees, but all of them in ahigher degree than those selected for making the bar ormalleable iron. We now proceed to describe the latterprocess.

(554.) Here the first step is refining the pig iron in the Refiu‘ n Srefinery or run out furnace. These are much less thanthe blast furnace, not being calculated to hold muchabove a ton. The pig iron being introduced into therefinery furnace, is kept in a state of fusion for abouttwo hours, during which it parts with a quantity of itscarbon and other impurities, and comes out, as the termimplies, much more pure than in its former state.

The furnace, as we have seen, is tapped every twohours, the yield each time being about a ton ; and the fur-nace being constantly worked by a double set of men,through day and night, ought to produce about seventytons of metal per week ; perhaps it may be considered tovary from sixty to seventy tons for each double furnace, thatis to say a furnace of larger dimensions than those deno-minated single furnaces, and furnished with two blasts in -stead of one only. The iron, from the refinery furnace, isrun into a long flat mould, varying of course in differentWorks, but commonly about twenty feet long and two fee 1broad: this is placed near the refinery furnace, and themetal, when the f urnace is tapped, passes from the furnaceto the mould, through a channel formed for the purpose.

The mould is set over a cistern of cold water, to facilitatethe processof cooling,and to cause the metal to setquickly,alter which it is easily broken down by hammers to fit 1(or the next process. The loss of weight sustained mthe refining amounts to about 10 per cent.; but it ocourse varies considerably under different circumstances.

Taking, however, 10 per cent, as a medium, the propertional yield at this stage, compared with the quantity oraw mine, will be about 29 or 30 per cent. puddling-

(555.) The next process is what is technically calledling , at a furnace called a puddling furnace, which widescribed in a subsequent part of this article. It wisufficient here to state, that about three or four hun re