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tended with fuccefs, and the opertions of the furnace pro- 

 ceeded «nth their ufual facihtv. 



After the apphcation of ileam enirines to raife and con- 

 denfc air, the quantity and ftrength of the blaft hecame 

 more a mechanical property in the hands of the niannlac- 

 tiirer. It was foon difcovered that an increafed volume of 

 air, by exciting a much higher temperature throughout the 

 furnace, conftituted the immediate adion of thofe affinities, 

 which the tall furnace accomplifhed by a long attenuated 

 contacl, and that iron equally carbonated and lilted for the 

 purpofe of melting, could be produced by 30 hours contact, 

 as in four days. 



The confequence of thefe gradual difcoveries was a gene- 

 ral predilection in favour of fmall furnaces, and at prefent the 

 bias of the manufafturer feems inclined to thiii extreme. 

 Where the maximum will be found it is difficult to conjcdliire, 

 for the ground which the manufacturer now occupies is 

 materially altered from what it was when fmelting with 

 coke was flrft introduced. The perfedion to which the blow- 

 ing machine has attained, forms a ftriking contrail to the 

 feeble and diminifhed efFefts of the bellows in the infancy of 

 the trade. So far as the neceiTary affinity is increafed, 

 and more inftantaneoufly produced in high temperatures, 

 ■than in thofe inferior, the manufafturer is differently 

 circumftanced, and commands an extent of means 

 unknown to him in former times. That this fup^riority 

 will produce equivalent effefts in the modification of the 

 blail-furnace, requires but little demonih-ation. Two fafts 

 illuftrative of this may, however, be mentioned. Caft fteel 

 has of late years been formed direftly from bar-iron, by a 

 procefs which only requires an hour or two to complete, 

 and with fmall quantities of matter the fame may be per- 

 formed in a few minutes. This is effefted by prefenting the 

 carbonaceous matter to the iron at a melting temperature. 

 In the ufual mode of cementation, bliftered fteel, by a more 

 attenuated contaft and inferior temperature, requires fix or 

 feven days to complete, what is here produced in two hours. 

 The difference of temperature in the two operations is 

 equal to 60" or 70'^ of Wedgewood. The firft operation will 

 be confiderably (hortened, if the caft fteel is required to 

 hold much carbon ; but if this requifite is ncceftary in the 

 bhftered fteel, the length of the cementation mull necef- 

 farily be protrafted. Again, a piece of malleable iron may, 

 by prefenting it with a proper dofe of carbon, at a high 

 temperature, be converted, in a few minutes, into a mafs of 

 the richeft carburat^d caft-iron, which, in a temperature in- 

 ferior, would have required feveral months. 



The fame fafts will apply, in part, to the manufaflure of 

 pig-iron in the blaft-furnace ; but an unanimity of opinion 

 and aftion on this fubjeft is precluded, as well by the pre- 

 judices of individuals, as from circumftances arifing out of 

 the nature of the materials operated upon in different 

 places. 



A furnace has lately been tried at Muirkirk in Scotland, 

 only eight feet diameter acrofs the boflies, in place of its 

 former dimenfions, which were ten feet, aad 40 feet high. 

 It was foon found, that with the fame volume of blaft which 

 was formerly applied to the ten feet furnace, very inferior 

 «ffe£ls were now produced. The combuilion apparently was 

 carried to too great an extent, and the materials,- owir.g 

 to this circumftance, entered into fufion before the iron had 

 imbibed a fufficient dofe of the coally principle from the fuel. 

 Another great evil which refulted from tiiis diminution of 

 diameter, was a friftion, or retardation of the defcent of the 

 materials upon the lining of the furnace. This evil was in- 

 creafed and the materials made more bouyant, by the ufual 

 TclumeiOif air elevating itfclf in a cone not much mere than 



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half its former area. The confequer.ces were, that th„- 

 whole mixture of coke, iron-ftone, and lime-ftone, would 

 have frequently hung for an hour together, or until the 

 blaft had cut all the hearth and bofties clear of materials, 

 a flip would have then enfued, and brought with it a large 

 proportion of newly introduced matter. The introduclijr; 

 of this into the fufing point before being properly heated, and 

 Jong before any affinity had been ellabiiftied betwixt the 

 particles of metal and the carbon of the furnace, invariably 

 changed the quahty of the metal, and caufed frequent 

 and ludden alterations from grey to white iron. 



Upon the fubjeft of height and width of blaft-furnaces, 

 it may be finally remarked, that the average height m Bri- 

 tain may be taken at forty feet from the upper furface of the 

 hearth bottom, eleven feet diameter at the greateft width ov 

 bodiings, and three feet and a half for the diameter of the 

 tunnel-liead, or furnace-moutli. 



If the proportions of height and diameter in the dimen- 

 fions of tiie blail-hirnace have given rile to a multiplicity of 

 opinions, the internal ftructure and ftiape of the cavity have 

 been no lefs an iiniple field for fpeculation and prejudice. 

 At one time this was conceived fo efTential to the fuccefs of 

 iron-making, that any particular furnace that had made 3 

 fortunate run of quantity and quahty, was copied with the 

 greateft accuracy of delign. 'I'he fortunate i ion -mailer in- 

 genioufly attributed to the mechanifm of his own conftntc- 

 tion the rich and fuperior harvtll he had reaped in metai, 

 and faw, or fancied he favv, in 'the curvature 01 a lire, or i« 

 the iHclination of a Hope, the tahfman of his good fortune. 

 By prolonging the one, or depreffing the otiier, he imme- 

 diately inferred that ftill fuperior effects would be produced, 

 and that by obtaining the perfeftion of ait in the mere fabr - 

 cation of ftrutlure, evei7 thing that was great and powerful 

 vi-ould enfue. This rage co.itinued for many years, and 

 gave rife to an endlefs variety of fliapes, many of which, in 

 their eventual fuccefs, Lad only the merit of originality tn 

 boaft. 



In the eftabUftiment of this important and national manu- 

 facture, the great fluctuation of opinion as to ftrudure 

 feems to have been the prelude to afubfidence into app.-'oved 

 forms, founded^ upon general principles ; and though we 

 may now fmile at the indifpenfible forms which our pre- 

 deceffors, or even contemporaries, annexed to the blall-fur- 

 nace, yet thele alterations of ftiape and llruclure lay the 

 ftrongcft claim to our refpecl and giatitude. The path i> 

 now opened, and the ground already beat ; from the labours 

 of thofe who have already gone before us, refult the hap- 

 pieft effefts ; we proceed towards our objeft, free from the 

 interruption which inexperience always entails ; and we may 

 now, by the direct application of principle, perfect with faci- 

 lity what may ftill be deemed defidei-ata in this important 

 branch. 



The varieties of (hape which cuftom and experiment, fronn 

 time to time, had annexed to the blaft-fumace, may be 

 claffeJ Underfour diftind kinds. P/atc\'U. and VIII. The 

 following defcription, characteriiing the refulting propertiei 

 and dimenfions in the form of each clafs, will be nectffary for 

 comprehending the fubject thoroughly. 



P/titeVll.j!^. I. is the vertical feiftion of the blaft-fumace 

 cut acrofs the top of the hijlhes ; the internal (hape entirely 

 conical ; the extcnial figure a qiradrangalar pyramid. The 

 conrtruition of this furnace is truly fingular ; and from thi* 

 alone great advantages were expected to refult. The origi- 

 nality of the principle connrts in the double Iquare, or throat. 

 One immediately above the hearth, not repreftnted in this 

 figure, but fimilar to the fquare in P/ate IX. Jig. i. B : and 

 another half way np the cone, four feet in diameter ; fee A. 

 4 B z B, the 



