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6 feet long ; it reaches underneath at least half of the dam-stone b. This bottom stone 

 is well bedded in fire-clay, mixed with three-fourths sand. After tho bottom stone 

 is placed, the upper part of which must bo three-fourths of an inch lower at tliu l;nn- 



stono than at the back, the two 

 side stones, c, are laid embedded 

 in fire-clay. These stones must 

 be at least 6 feet and a half 

 long, reaching from 18 inches 

 behind tho crucible to the middle 

 of tho dam-stone. Their form is 

 most commonly square, that, is, ;i 

 prism of four equal sides ; tho 

 transverse section of the grain 

 must be in all cases placed to- 

 wards the fire; the side stones 

 are sometimes square, but often 

 bevelled according to the slope of 

 the hearth. Upon these stones 

 the tuyere stones, d, are bedded ; 

 the latter suffer much from heat, 

 and therefore ought to be of 

 the best quality. They should 

 be from 20 to 24 inches square, 

 or even larger : the tuyere holes, 

 /, a kind of taper arch, are cut 

 out before the stones are bedded. 

 These stones do not reach further 

 than to the front or tymp-stone, g, 

 and are therefore scarcely 4 feet 

 long ; the top stone e, is generally 

 sufficiently high to raise at once 

 the crucible to its destined height. 

 After both sides are finished, the 

 back stone / is put in, and then 

 the tymp-stone, g ; the space be- 

 tween the hearthstones and tho 

 rough wall of the furnace stack 

 is filled and walled up with 

 common brick or stones. 



In starting a charcoal furnace, 

 it is first thoroughly dried by 

 burning a fire for several weeks 

 in the interior, which has a 

 temporary lining of bricks. Tho 

 lower part of tho furnace or the 

 hearth is then filled gradually 

 with charcoal, and when the fuel 

 is well ignited, and the furnace 

 half filled, ore may bo charivd 

 in ; but it is sometimes ailvisaMe 

 to increase the draught by form- 

 ing grates by laying across tho 

 tymp a short iron bar, as high up as the dam-stone, by resting upon this bar six or 

 seven other bars or ringers, and by pushing their points against the back stone of 

 the hearth. There is not much iron made during the first 24 hours ; most of tho 

 ore is transformed into slag, and the iron which comes down gets cold on the butt- mi 

 stone, where it is retained ; tho blast should not be urged too fast at first, but in- 

 creased gradually, in order to avoid the serious evil arising from a cold hearth ; if 

 all goes on well, the hearth will be free from cold iron or clinkers in a week, tho 

 yield of iron will increase, and tho burden may bo increased likewise. The average 

 charge of charcoal, which should be dry, coarse, and hard, is about 15 bushels. Ac- 

 cording to Overman's experience, the most favourable height for a charcoal furnace is 

 35 or 36 feet ; if below this standard they consume too much fuel, if above they an> 

 troublesome to work ; if it be desired to enlarge the capacity of a furnace, he thinks 

 it better to increase the diameter of the boshes, or to curve the vertical section. Th-To 

 is much difference of opinion amongst managers of furnaces on the subject of tho 

 proper size for tho throat of the furnace ; the tendency of narrow throats would seem 



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