B L A 



B L A 



by which the blaft enters the furnace. The termination of 

 the tapered pipe, which approaches the tuyere, receives fmall 

 pipes of various diameters from two to four inches, called 

 r.ofe -pipes. Thefe are applied at pleafure, as the furnace 

 B\ay be deemed to require an alteration in the volume or 

 denfity of the blaft. K, the bottom of the hearth, two feet 

 fquare. L, the top of the hearth, two feet fix inches fquare. 

 KL, the height of the hearth, fix feet fix inches. L, is the 

 bottom of the bofhes, which here ttmiinate of the fame 

 fize as the top of the hearth, only the former are round, and 

 the latter fquare. M, the top of the bofhes, twelve feet dia- 

 meter, and eight feet of perpendicular height. N, the fur- 

 nace-top, at which the materials are introduced, or, as it is 

 commonly called, charged ; three feet diameter. M N, the 

 internal cavity of the furnace from the top of the bofhes up- 

 wards, 30 feet high. N K, total height of the interior of 

 the furnace, or working part, 44! feet. OO, the lining. 

 Tliis is done in the niceft manner with fine bricks, from 

 tweWe to fourteen inches long, three inches thick, and ta- 

 pered to fuit the circle of the cone. PP, a vacancy which 

 is left all round the outfide cff the firll lining ; three inches 

 broad. Tliis is fometimes filled with coke duft, but more 

 often with fand firmly comprefTcd. This fpace is allowed 

 for any expanfion which might take place, either by an in- 

 crcafed volume of the furnace itfelf in heating, or by the 

 prcfFure and weight of the materials when defcending to the 

 furnace bottom. QQj the fecond lining, fimilar to the 

 firft. The objeft of this is to guard againft the entrance of 

 the flame into the mafs of common building, by rents which 

 may take place in the firfl lining OO. R, a call-iron lintel, 

 on which the bottom of the arches is fupported, eight feet 

 and a half long, and ten inches fquare. R.S, the rife of the 

 tuyere arch, fourteen feet high on the outfide, and eighteen 

 feet wide. VV, the extremes of the hearth ten feet fquare. 

 This, and the bofhing ftones, are commonly made from a 

 coarfe-gritted fand Hone, whofe frafture preftnts large 

 rounded grains of quartz connefted by means of a cement 

 Icfs pure. 



Fig. 7. reprefents the foundation of the hearth, and a full 

 view of the manner in which the falfe bottom is con- 

 ftruded. 



A A, the bottom ftones of the hearth. B, a ftratum of 

 bedding fand. CC, pafTages by which the vapour gene- 

 rated from the damps is pafTed off. DD, pillars of brick. 

 The letters in the horizontal view of the fame figure corre- 

 fpond to fimijjr letters in the dotted elevation. 



Fi^. 8. AA, horizontal feftion of the diameter of the 

 boflies ; the lining and vacancy for fluffing at M. C, view 

 of the top of the hearth at L. 



Fig. 9. V'ertical fide feition of the hearth and bofhes, 

 (hewing the tymp and dam-ilones, and the tymp and dam 

 plates, a, the tymp-ftone ; b, the tymp-plate, which is 

 wedged firmly to the fide wails of the hearth ; c, dam-ftone, 

 which occupies the whole breadth at the bottom of the 

 hearth, excepting about fix inches, which, when the furnace 

 is at work, is filled ever)- caft with a ftrong binding fand. 

 This ftone is furmounted by an iron plate of a confiderable 

 thicknefs, and a peculiar fhape, tl ; and from this it is called 

 the dam-plate. The top of the dam-ftone, or rather the 

 notch of the dam-plate, is from four to eight inches under 

 the level of the tuvere-hole. The fpace under the tymp 

 plate, for five or fix inches down, is rammed every call full 

 of ftrong loamy earth, and fometimes even with fine clay. 

 This is called the tymp ftopping. 



The fquare of the bafc of this furnace is 3S feet. The 

 extreme height, from the falfe bottom to the top of the 

 crater, meafures 55 feet. 



Vol. IV. 



BtAST Furnaces, ConflruSicn of. 



Thefe furnaces are fometimes built of an external qua- 

 drangular form, entirely of fand ftone, and lined, in contaA 

 with the fire, of the fame materials ; fometimes they are 

 built conical, entirely of bricks, or with fand ftone on the 

 outfide, and linings of both common and fine bricks 

 within. 



One great defideratum in the conftruclion of furnaces, is 

 to counteratl the effects of a powerful expanfion, which al- 

 ways take place, to a greater or lefs extent, after heating, 

 and the introduftion of the blaft, and which has frequently 

 proved fatal to the exiftence of the entire fabric. 



In the general ilyle of building, all are agreed that the 

 pillars, which fupport the arches, and of courfe the whole 

 fabric, ought to be done in the moil fuhftantial manner. 

 But beyond the arches, a variety of methods has been 

 adopted to enfure a complete fabric, free from large open- 

 ings or rents after a few weeks blowing. 



Some iron-mailers are of opinion, that the fame degree of 

 firm building, that is bcftowed upon the pillars, ought to 

 be continued to the top, with the addition of binders of flat 

 iron preffing with their edges againft the body of the building, 

 or with four fcrewed bars, ftill paffing through the external 

 building, and forming one fquare binder, if the fhape of the 

 furnace is quadrangular. Another fpecies of binder is ufed 

 for fquare piles, made of caft iron of a prodigious ftrength 

 and weight. The individual pieces forming this binder, 

 have, at their extremities, mortifes, which mutually receive 

 each other, with a confiderable extra fpace for the expanfion, 

 which is invariably experienced afterwards. Other iron- 

 mafters, again, prefer rearing a fuhftantial (hell of building, 

 and filling the interior fpace towards the linings, either with 

 dry bricks, or ftones loofely laid together. When the mafs 

 of building becomes thoroughly heated by the kindling of 

 the fire, and the introdudlion of the blaft, the interior of the 

 furnace expands confiderably, and the aftion is fuppofed to 

 be merely confined to the wedging together of the loofe parts 

 of the building. By the time that this is effefted, the ex- 

 panfion is fuppofed to have ceafed, and the exterior fhell of 

 the furnace is preftrvcd entire. Others, equally anxious to 

 form a perfeft building, have given an octagonal form to 

 that part of the furnace above the arches, that the 

 binding might be more happily effected. Some have 

 affumed this fonri, with the addition of femi-circular re- 

 cefTes in the fides of tlie oftagon ; their convexts being 

 llrongly arched to refill the powerful preluire expected from 

 within. 



Still more determined to defy the all-powerful effcfts of 

 expanfion, others have hollowed furnaces from the folid rock, 

 forty to fifty feet high, and lined thefe immenfe perforations 

 with fine bricks in the ufual form. 



Where fuch a variL-ty of form and of method exifts in ef- 

 fedting the fame purpofe, and where the inftances of expe- 

 riment have been very numerous, every mode of conftruction 

 can boaft of a folitary inftance of complete fuccef?, except- 

 ing in the cafe of the rock, which was only once attempted, 

 and which, after the introduction of the blaft, opened from 

 four to fix inches from top to bottom. 



There are fo many circumftantes to be taken into the ac- 

 count, befides the mere form of the buildinj-, that unlefs thefe 

 are all equally guarded againft, the chances arc in favour of the 

 furnace opening confiderably. If the building isconftructed 

 of fand ftone, and if tliis material is carried from the quan-v- 

 as it is wanted by the workmen, an immenfe proportion of 

 water is thus introduced, which by a little forefight might 

 have been avoided. Sand ftones of common dcnilty as to 

 frafture, contain, when taken immediately from the quarry, 

 4 B from 



