B L A 



from 8 to lo per cent, of water, and coarfer-gritted ftoiies 

 from 10 to 12. TakinsT the average lo per cent., then in 

 a furnace of equal dimeiifions to the drawing in Plate II. 

 Jig.6. the faiid Hone of which will weigh upwards of J200 

 tons, there will be introduced izo tons of moillure. This 

 quantity is always confiderably increafed by the portion of 

 water necelTaiy to reduce the lime to mortar, and trcquently 

 augmented by the moift ftate of the weather during 

 building, . 



The evaporation of this immenfc body of w?ter is the 

 fource of all the mifchief which takes place in the fhell of 

 the blaft furnace; nor is it much to be wondered at, where 

 every precaution is not ul'ed to bring tl>c heat forward in 

 the moll gradual manner, prefcrvii.g the clcarnels of the 

 ▼ents, and allowing the moiliure inftiilibly to pafa away. 



In fituations where bricks can be obtained, the moifture 

 of the fand (lone is avoided, but the great extra quantity of 

 lime, which is neceffary to build with bricks, introduces 

 througli the medium of the mortar an almoll equal quantity 

 of water, as with farrti ftonc. This has been obviated in 

 part by ufuig foft clay in the interior of the walls ; but as 

 clay feldom binds to any great extent, the general pulh 

 of the furnace mull be trufted to good binders from 

 without. 



In the conftruftion of all blaft furnaces, a complete vent- 

 age ought to be preferved by means of narrow flues, or paf- 

 fages proceeding horizontally from the middle of the folid 

 Hiell, or within two feet and a half of the interior to the 

 outfide. Thefe ought to be connefted with a circular chan- 

 nel, or gutter, of the fame dimenfions, proceeding round 

 the circumference of the furnace ; fo that, if any one vent 

 were choaked in the general expanfion, the moillure con- 

 dufted by it might eafily vent itfclf among the other open- 

 ings. The vents cannot well be too numerous ; and as they 

 feldom exceed four inches fquare, the building cannot be 

 materially weakened by them. 



In addition to the horizontal channel of communication, 

 feme builders carry up in the main building of the furnace 

 four, fis, or even eight perpendicular flues, which commu- 

 nicate with it and the openings that proceed horizontally to 

 meet the external air. See Plate WW. f^^. i, 2, 3, 4. 



Either of thefe methods may be confidered as juft precau- 

 tions to enfure the exillence of the furnace, but adopting 

 them in the fuUell and moft. complete manner, is not always 

 accompanied with fimilar fucctfs. If circumllanccs formerly 

 roticed concur in occafioning an extra degree of expanfion, 

 the preffure of the lining againft the common building of the 

 furnace often deranges the fyllematic order of the vents, 

 puflies the bncks into contact with each other, and fir.o- 

 ihers for a little while, though to gain more fatal elaltic ef- 

 fefl!^, the increafing volume of the vapour. 



Ak;.r fuch a diverfity of opinion upon a fubjeft of fuch 

 general importance, wherein each refpeclive clals of votaries 

 can boall of complete fuccefs from its peculiar plan, it may 

 be difficult to point out one more generally attended with 

 good effefts than another. The following, hovvever, may 

 deferve the ferious confideratiou of the manufacturer of 

 pig-ifon. 



Of whatever materials the furnace is conftruded, let them 

 poflefs no more moillure than is fnflicicnt for their proper 

 building. The thicknefs of the common building not to 

 exceed, at its greatell breadth, 6i, or 7 feet. In the middle 

 of the wall, a fpace of four or fix inches ought to be left 

 clear all the way to the furnace top. Into this vacuity Ihould 

 be introduced fmall fragments of faud-ilone, about the lize of 

 an egg and under. When the expanfion, preceding from the 

 hrc building of the interior, caufes the bricks immediately in 



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contail to pu(h outwards, the malFcs of fand- (lone are im- 

 mediately reduced in fize, and tilhng the interftices occafioned 

 by their former angular fliape, adiually occupy much lef» 

 room ; and now prefent to the flame or fire, fliould it be in- 

 clined to penetrate fo far, a folid verrical ft^ratum of fand, 

 after having fecured the expanfion of the furnace to the ex- 

 tent of fome inches. The effefls of the preffure are thus 

 diverted from the (hell of the building, and loll in the pul- 

 verization of the fragments of fand-ftone. 



The advantages refulting from this plan may be nearly- 

 doubled, by ufing a double lining of fire bricks, as repre- 

 fentcd in Plate VIII. Jig. 3. betwixt each of which, and the 

 common building, a fimilar vacancy Ihould be left ; but 

 filled with fharp land, containing no more moillure than ferves 

 to compaA it into a firm body. As this moillure becomes 

 gradually expelled in the (low heating or annealing of the 

 furnace, the fand occupies lefs bulk, or, which is the fame 

 in effeft, is then iufceptible of a greater degree of compref- 

 fion when the general expanfion of the furnace comes on. It 

 is evident that the force is here alfo diverted againft the fand, 

 in place of afting immediately, with a tendency to enlarge 

 the circumference of the bailding. 



Over and above all thefe precautions, the annealing or 

 drying of the furnace in a progrefGve and regular manner 

 ought to be carefully attended to and continued for two or 

 three months at leaft. Many are blown much earher, from 

 an anxiety to get to work, and make returns for the great 

 capital ncceffarily expended in thefe undertakings. 



The fame variety of opinions exifts in the trade, relative to 

 the determined figure and dimenfions of the blaft furnace, as 

 fubfift, with regard to the beft mode of building. Its height 

 has, at different times, varied from 20 to 70 feet; and 

 its diameter, at the bodies, or wideft part, from 8 to 

 15 feet. It will be eafy to trace the fource of this 

 indefinite mode of conllruAion, and the uncertainty which 

 muft neceflarily pervade operations of fo much rilk and 

 importance. 



At the time when charcoal of wood was the common, and 

 indeed, the only fuel ufed in the blaft furnace, the volume 

 and extent of the blaft were proportioned to the very iniper; 

 fc£l ftate of the blowing machinery. Long experience had 

 taught the manufafturer what were the proper fize and di- 

 menfions of his furnace. Many of them were from 12 to 

 18 feet high, and fome of them, where a^good water wheel 

 blaft exilled, reached as far as 28 feet in height. 



When pitcoal was introduced into the blaft -furnace, in the 

 ftate of coke, to produce fimilar effefts to the charcoal of 

 wood, it was foon tound, that in furnaces of equal capacity 

 and height the ftme eft'ccls could not be produced. The 

 ore required to remain in coniaft with the ignited fuel for a 

 longer fpice of time, in order, unqueftionably, to produce, by 

 attenuated contatl, what was deficient in temperature, for 

 the latu ration of the ore with coally matter. This would 

 immediately fuggeft an increafe of the height of the blaft- 

 funiace ; and if beneficial efl"e6ts once refulted from a ftep of 

 this natui-e, it became a matter of difficulty to fay where the 

 progreflio;; of height would ftop. 



Hence, in a few years, arofe furnaces of 40, 50, 60, and 

 70 feet in height. Of the laft dimenfions, one was erefted 

 in Wales. The fize of the artificial crater was fuch, that 

 the ftiength of the blaft was fcarcely fufficient to keep the 

 exiftence of flame vifible at the fuinace top. After in vain 

 endeavouring to ignite the immenfe body of materials con- 

 tained in its vaft capacity, the height of the furnace was re- 

 duced 30 feet by cutting a hole in its fide, narrowing tha 

 mouth, and throwing in the materials at the height of 40, 

 in place of 70 feet from the furnace bottom. This was at- 

 tended 



