42 Defcription of a Blaft-Furnace, &eg 
allowed for any expanfion which might take place in confe~ 
juence of the fwellme of the materials by heat when de- 
fcending to the bottom of the furnace.—QQ, the fecond 
Nning, fimilar to the firft.—R, a caft iron lintel, on which 
the bottom of the arch is fupported.—RS, the rife of the 
arch.—ST, height of the arch; on the outfide 14 feet, and 
18 feet wide—VV, the extremes of the hearth, ten feet 
fquare. This and the bofh-ftones are always made from 2 
eoarfe oritted freeftone, whofe fracture prefents large rounded 
grains of quartz, connected by means of a cement lefs pure. 
Figure 2 reprefents the foundation of the furnace, and 2 
full view of the manner in which the falie bottom 1s con- 
firucted, 
AA, the bottom ftones of the hearth. B, ftratum of 
bedding fand. CC, paflages by which the vapour, which 
may be generated from the damps, are paffed off. DD, pil- 
Jars of brick. The letters in the horizontal view, of the fame 
firure, correfpond to fimilar letters in the dotted elevation. 
Fieure 3, AA, horizontal fection of the diameter of the 
bofhes, the ming and vacaney for ftuffmg at M. C, view 
of the top of the hearth at L. 
Vicure 4, vertical fide-fection of the hearth and bofhes ; 
fhewing the tymp and dam-ftones, and the tymp and dam- 
plates. a, the tymp-itone. 5, the tymp-plate, whieh is 
wedged firmly to the {tone, to keep it firm in cafe of fplitting 
by the great heat.—e, dam-ftone, which occupies the whole 
breadth of the bottom of the hearth, excepting about fix 
inches, which, when the farmace is at work, is filled every 
éaft with ftrong fand. This ftone is farmounted by an iron 
plate’ of confiderable thicknefs, and of @ peculiar fhape d, 
and from this calle¢ the dam-plate. The top of the dam- 
ftone and plate is two, three, or four inches under the leve} 
of the tuvere hole. The fpaee betwixt the bottom of the tymp 
and the dotted’line is alfo rammed full of ftrong fand, and 
fometimes fire-clay. This is called the tymp- flopping, and 
prevents any part of the blaft from being unnecellarily ex- 
pended. 
The fquare of the bafe of this blaft-furnace is 38 feet 
the extreme height from the falfe bottom to the top of the 
erater Is 55 feet. 
XI, Extreé 
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