IRON. 



jound, lias not/ as we have yet heard, been direftly afcer- 

 tained by experiment. An inquiry, undertaken w'ith this 

 view, would, however, be of great importance to tlie iron- 

 iTiafter. It might be efFeftcd in two ways ; firft, by mixing 

 •different proportions of the materials employed ; and, fo- 

 condly, by a direct analyfis of the moft fufible part of the 

 blaft-fnrnace cinder, and that with which the bcft and moll 

 carbonated iron has been produced. The cinder v,-hich 

 Jufes at the lowed temperature will be beil known by its 

 -frafture after cooling. It may, in general, be deemed good 

 in proportion to its earthinefs when folid, and particularly 

 iliould the outer cruil appear glaffy and tranfparent. A 

 reafon may be given for this appearance, by reference to 

 fome fadls announced by fir J.nties Hall and Dr. Hope, in 

 accounting for the opacity of the whin-done. They found 

 that when common flint-glafs, wliicli is Kiore lufihle than 

 ;the blad-fiirnace cinder, was allowed to cool flowly, the 

 niafs became opaque, and put on a ftony appearance. 

 They hence conceded, tliat the whin-done might have been 

 tranfparent, and have poflefled a gl.ifTy frafture, had it been 

 cooled i-apidly. The inference to be drawn from this will be 

 obvious ; for the more fufiblc the cinder, the longer it is in 

 ■cooling, and confequcntly the more opaque. What 

 ftrengthens riiis idea, too, is, that the exterior of a mafs of 

 binder is more tranfparent, almoft condantly, than the inte- 

 -rior ; and the centre of that in particular, under which the 

 bed iron is made, having a ftony frafture, with a thin vitre- 

 ous flicU furrounding its outfide. In beginning to work 

 .any new ore of iron, ihe firll Hep is to analyfe it, both in the 

 dry and humid way. By the iird, we get'the jjfr rentage of 

 iron in the one ', and by the fecond, we become acquainted 

 ■B'ith the quality and proportions of its earthy matter. The 

 next ftep is to analyfe the coal to be employed, for the pur- 

 pofe of afcerlaining the quantity of carbon it contains, and 

 alfo the nature and proportions of its earthy refidua. Thefe 

 fails being clearly mai!e out, there will be nothing neceffary 

 "but to add to thefe materials a proper mi.Kture of fuch fub- 

 ■fiance as will m.ake the mod fulible cinder. If the ore be 

 iargiUaceaus, or, in other words, if clay predominate, lime is 

 to be the material employed. Indeed, ores of this defciiption 

 .are fo very common, that lime ha.s been thought the only 

 /ubftance to be ufed, under all circumdances, for the pur- 

 pcies of a flux ; and fo completely ignorant have the iron- 

 makers been of tlie philofophy of the procefs, that it has 

 ■even been attempted to be added when the ore has already 

 -abounded with calcareous ingredients. 



Keeping in view the principles we have juft laid down, 

 the management of tbe calcareous ore will be equally ca^'y 

 -with the mode of working the argillaceous ; fince, in fuch 

 .cafe, we have only to employ clay for the flux indead of 

 lime. But the bed method would, perhaps, be, if the com- 

 ponent parts of an argillaceous and a calcareous ore were 

 fufficiently well known, to mix the two together in proper 

 jroportinns. 

 - Whatever may be the fubdance employed, whether it be 

 iimeftone for an argillaceous ore, or clay for a calcareous ore, 

 it diould be very minutely analyfed, as thofe fubdanccs are 

 'fcarcely ever found in a date of purity. The lime (honk!, if 

 •poUible, be the Ibell linicllone. At all events, the magr.efian 

 jVratum Ihou'd be avoided, fince that fubdance tends mi:ch 

 -to iefltn the fulibility of earthy compounds. Some fubdanccs, 

 to which we give the name of clay, frequently confirt of a 

 Isrge proportion of fome other earth. 



Auother thing to be attended to, alfo, is the ftate of oxy- 

 idatioii in which we find the iron-ore. 



If it be highly oxrdated, more of the carbonaceous matter 

 «riil .fee required for its reduction, and in all probability a 



longer time; but, befides this, a greater quantity of the 

 oxyd of iron, will combine with the earthy matter, which, 

 although it may contribute to the fufibility of the cind.v, 

 a large portion of the iron will be loft. On the contrary, 

 when the iron is in a low ftate of oxydation, the whole of 

 the iron may be apt to combine with the carbon, and the 

 earthy matter may not get a fufficient quantity of the 

 oxyd to render it, in a proper degree, fuiible. In fuch 

 cafe, it would be neceffary to add fonle oxyd of iron, wliick 

 might more eafily vitrify and enter into the compofition of 

 the cinder. 



The coal employed in the fmelting of iron, for the pur- 

 pofe of being coked, is commonly laid in heaps in the open 

 air, and afterwards fet on fire. , When the combufiion has- 

 gone on to a certain degree, the fire is checked by covering 

 it with dud and preventing all poffible accefs of air. For 

 farther particulars, fee Coke. 



It is effential that the coke diould be harder than it can 

 generally be made in the open air without corUiderable 

 v\ ade ; and we recommend, therefore, the method employe<l 

 in making the cokes for melting fieel. The coal, which is 

 very foit, is piled up in ovens of the fliape of an creA 

 frui'uiii of a cone. The air is let in at an aperture near 

 to the bottom, which is contradled in fize as the coinbuftion 

 becomes rapid, and ultimately clofed. The whole mafs 

 will at this time have acquired fuch a degree cf heat, as 

 not only to drive off all the volatile matter, but to render 

 the coke extremely hard. There is a confiderable faving 

 in this mode of coking, and the coke is not only more com- 

 padl, but better adapted for the generahty of ores of iron. 



In fmelting the argillaceous ore, the proportions of ths 

 roafted ore, and the limedone, are governed entirely by the 

 coke employed. The latter is always a fixed quai.tity, 

 and the ore and limedone are varied according to the quality 

 of the iron to be made and the working order of the fur- 

 nace. In proportion as more or lefs of lime and ore are 

 added to the dandard quantity of coke, the furnace is faid 

 to carry a greater or lefs burthen. 



It would be u.Q-lefs to give any precife proportions of the 

 ore and limedone to a given quantity ol the fuel, iince they 

 are found to vary with the nature of the coal in uk- ; 

 and, wh.it is not a little remarkable, the proportions will 

 frequently vary in two furnnces working with the fame 

 coal, and even in the fame furnace at different limes. 



The burthen of the furnace will alfo vary with the- 

 quali'y of iron to be made, that is, as it is required to con- 

 tain more or lefs carbon. In making the dark-grey iron 

 called N' I, and which contains the greateft proportion of 

 carbon, the burthen mull be lefs than that required to make 

 the lefs carburetted iron, commonly called white iron, or 

 forge.pig. ' 



To give a general idea of the proportions of the ma- 

 terials, we fliall prefent in detail, the quantities ufed at a 

 blad-furnacc, making in general good melting iron, which 

 is of an intermediate qua'ity between N I and the forgr-pig. 

 The ore is argiUaceou.s, containing about 27 per cent, of 

 iron ; the coal rather foft, but having a good proportion 

 of carbonaceous matter ; and the limedone good, being of 

 the flic ly kind before fpoken of The furnace is about 45 

 feet high, and I2.§ feet diameter in the v.'ideft part. It 

 works with a bright tuyere, and receives from the blad 

 about 2500 cubic feet of air in a minute, through a cir- 

 cular aperture of 2^ inches in diameter. 



The average charges of coke per Jhift, as it is termed, 

 or in the fpace of 12 hours, are 50 (each 2^c-:ut.), or nearly 

 feven tons. The calcined ore for good meiiing iron is about 

 the fame quantity j and for forge-pigj or the lead carburetted 



variety. 



