IRON. 



tongs under a large hammer, dsnominated, ns applied to 

 this parti .-iilar ufc, z Jlamphi^ l.ammfi; wiierc it is beaten 

 into cakes, which are afterwards broken up, and treated in 

 the balling furnace as before defcribed. This is the old 

 mode of working, and the iron obtained from it is by many- 

 conceived to be of very fupcrior quality. The heat pro- 

 duced is confidcrably inferior to that afforded by coke in 

 the run-out furnace ; and the iron is lefs furrounded by tlie 

 fuel than in the cafe ju'.l mentioned. The prcfont charcoal 

 fire is properly a refinery, and not t!»e one which is ufed 

 merely as a prchminary to the proccfs of puddling. Here, 

 the indinefs of decarbonization is at once completed ; and 

 the refulting metal is in the fame (late of purity as that 

 yielded from the rollers, after it has been puddled by the 

 other method. Balling and blooming follow in regular fuc- 

 ceflion, and plates or bars are produced exaftly as before. 



According to the fccond mode of treatment, in which 

 llooming is omitted, the maffes obtained from the bttlUng fur- 

 nace are reduced under the hammer into the form of lohd, 

 cubical blocks ; and vvh.en their temperature is tsio much 

 lowered to be capable of any farther working, they are again 

 heated in a fire called a chafery, which is urged by a power- 

 ful pair of bellows, and fcarccly differs from a common 

 fniiih's forge, except in being lai-ger, and the cokes upon 

 It being helped up to the unufual height of at leail two feet. 

 In this fituation they are raifcd to the point of welding, and 

 afterwards hammered out into ingots of a flattened (liape. 

 Iron bars are united to them very fliortly after they are 

 brought from the laV.ing furnace, to afford a greater facility 

 of management, in the fame manner as was defcribed in the 

 making of blooms ; and thefe, as before, are detached, when 

 the ingot is fufRciently formed. The iron produced in this 

 way is- not confidered fo good as that afforded by either of 

 the other proceffes, and is employed, for the moll part, in 

 the commoner fervices of art. Repeated rolling, or ham- 

 mering, is the only means of imparting the ribrous texture 

 fo neceffary to good bar iron ; and as this treatment is lefs 

 frequent in the prefent mode of operating, the deficiency of 

 value in the material obtained may very probably be referable 

 almoll exclufively to this circumilance. 



The above include the whole of the important variations 

 that are prefented in the manufadure of bir iron. Other 

 fhades of difagreement may be traced in different works ; 

 but they are of a nature too trifling and unimportant to merit 

 any particular enumeration. The art is ftill in its infancy ; 

 and the light of chemical fcience, by being brought to a 

 focus here, cannot fail to difclofe many impiovements in the 

 prefent modes of procedure, which will greatly abridge the 

 expence now incident to this valuable branch of national 

 itiduftry. That the mere abftraftion of about 4 psr cent- of 

 carbon fhould require a facrifice, in effecling it, of above 

 40 per cent, of iron, appears monftrous beyond example : 

 and as thofe who are connected with the art become more 

 fcientific in their views, we (hall unqneilionably find that it 

 will be much more economically accomplilhcd. 



When iron has been completely freed from carbon, and 

 has acquired its highell degree of malleability by repeated 

 hammermgs, it is by far the moll tenacious of all the metals, 

 and is capable of being drawn into the fined wire. 



The tenacity of iron, as well as of all the reft of the 

 malleable metals, varies confiderably according to its foft- 

 nefs. After iron has been kept in a red heat tor fome time, 

 and fuffercd gradually to cool,' it becomes remarkably 

 changed in pouit of foftnefs. By being hammered, drawn 

 into wire, or rolled, it increafes in hardnefs to a certain ex- 

 lent j but, at the fjme time, partly lofes its malleability. 



By this mechanical treatment, when cold, its ftrcngth er 

 tenacity increafes ; and it may betaken at one point, when 

 it will require a far greater weight to break it, than if it 

 were hammered cither more or Icls. 



All the experiments yet publiflied relative to the tenacity 

 of iron, and the other metal% arc on this account very de- 

 fcdive. The writer of this article has fcen an iron wire, 

 when newly annealed, break with a weight of 50 pounds ; 

 but, after being drawn through two holes of a wire plate, 

 bear above twice that weight, without fullaining injury. 

 Iron, when properly annealed, will bear more bending 

 backwards and forwards before it breaks, than in any other 

 Uate : but the llrcngth, or that power which refifts a weight, 

 exerted longitudinally to break it, is jointly as the lail pro- 

 perty and its hardnefs. Hence the reafon why its llrength 

 is increafed with a certain degree of hammering. The fpe- 

 cific gravity of malleable iron, according to Briffon, is 

 7.7SS; that of pig iron being 7.207. Iron, in a Hate of 

 purity, requires fo great a heat for its fufion, that the bell 

 crucibles are nearly ready to mcU w'ith it. It has, however, 

 been fufed, and call into an ingot. It is faid to liquify at 

 158" of Wcdgewood. Its malleability is greatly increafed 

 by heat ; and by raifing it to a very high temperature, it be- 

 comes exceedingly foft, mid may be brought fo near to ab- 

 folute contad with another piece fimilarly heated, that th-.-y 

 unite firmly together. This procefs is called ivelding. Its 

 great affinity for oxygen, when heated to a welding point, 

 would very loon reduce it to an oxyd, if it were not for thii^ 

 vitreous matter fufing upon its furface ; and it may be (liH 

 more completely defended, by dipping it in powdered g^afs 

 or fand. See Difcription of Plates at the end of the ar- 

 ticle. 



2. Steel. — This fubftance, which is a compound of iron 

 and carbon, but in lefs proportion than that of pig iron, u 

 of fuch dillinguifhed importance in moll of the arts, that no 

 other fubftance could be fubdituted, capable of fupplying 

 its united properties of hardnefs, tenacity, and clallicity. 

 After the pig iron is totally deprived of carbon, and be- 

 comes malleable, the metal can be re-impregnated with that 

 fub'.lance to a certain extent, without loling much of itS- 

 malleable property. 



It is curious to remark, that although we have made iron 

 of excellent quahty in this country, for all the nice purpofes 

 to which it is capable of being applied, yet, in attenipting 

 to convert it into Heel, we have always failed ; the lleel 

 being red-fliort, and otherwife bad. It, of late, however, 

 has been fo great a defideratum to obtain flcel from Britifh 

 ore, in confequence of our want of communication with 

 Sweden and Riiffia, that feveral efforts have been lately 

 made to bring about this defirable object, and not altogether 

 without fuccefs. We may yet entertain a hope, therefore, 

 that the time luill arrive, when we fhall not be dependent on 

 other countries for this ufeful commodity. 



The only Heel at prefent, on -.viiich pcrfeft reliance can 

 be placed, is made from i'ome of tli-- bell marks of Swedilb 

 iron. The bars are ihmpcd with certain letters or charac- 

 ters, well known to the fleel-makers ; and fome of them 

 have preferved their charadlcr for making good lleel during 

 a long feries of years. 



The fize of the bars varies from 3 inches broad and i inch 

 thick, to about 2 broad by '^^ thick. 



Nothing more is necefl'ary to impregnate the bars of iron 

 with caibon, by which they become Iteel, than to ilratify 

 them with powdered charcoal in a clofe veffel, called a ce- 

 menting pot ; expofing the f.uiie to a degree of heat as little 

 ftioii of what would fwfe vue ilwl as uoffible. 



The 



