948 



IRON 



four arches are loft, the back and sides are called hii/crt-. /tn.'s, the front is called the 

 cinder fall ; the bottom of the furnace is formed either of large blocks of coarse sand- 

 stone or of large fire-bricks. The materials arc charged into the furnace through the 

 tunnel-head, which is provided with one or more apertures for the purpose. The 

 general form of a blast-furnace is shown u\J(g. 1222, and the following measurements 

 represent the interior structure of two that worked well : 



No. 1 

 feet 

 Height from the hearth to the throat or mouth . . 45 



of the crucible or hearth 6 



of the boshes 8 



of the cone 30^ 



of the chimney or mouth ..... 8 

 Width of the bottom of the hearth 1 . . . 2 



at its upper end 3 



of the boshes 2 12 



at one-third of the belly 12 



at two-thirds of ditto 8 



at mouth 4 



Inclination of the boshes * 59 



No. 2 



feet 



49 



6 



7 



30 



.3 



ill 



s 



6? 



1222 



Fig. 1223 represents the hearth and boshes in a vertical side section, a is tho 

 tymp-stone, and b the tymp-plate, for confining the liquid metal in the hearth ; 

 the latter is wedged firmly into the side-walls of the hearth ; c is tho dam-stone, 

 which occupies tho whole breadth of the bottom of tho hearth, excepting about 6 

 inches, which space, when the furnace is at work, is filled before every cast with 

 a strong binding sand. This stone is faced outside by a cast-iron plate d, called 

 the <&m-plate, of considerable thickness and peculiar shape. The top of the dam- 

 stone, or rather the notch of tho dam-plate, lies from 4 to 8 inches under tho level 

 of the tuyere-hole. The space under the tymp-plate, for 5 or 6 inches down, is 

 rammed full for every cast with a strong loamy earth or even fine clay, a process 

 called tymp-stopping. 



The blowing-machines employed in Staffordshire are generally cast-iron cylinders, 



1 Tho width of the hearth differs greatly in the furnaces in ditTm-nt localities. In Protlsm-l it 

 varies from 6 to 8 feet ; in the Welsh furnaces from 5 to 8 feet. When coke is used as fuel, M r. 'I'm ran 

 thinks 6 feet a sufficient width for all purposes; but with coal, with full-sized furnaces, 16 to P. fcvt 

 across the boshes, he thinks a 7-feet hearth to be more advantageous. 



* The diameter of the boshes in some of the Welsh furnaces is as much as from 18 to 19 f< < t. 



' The angle with which the boshes rise in different furnaces varies from 50 to 80. Mr. Trnran 

 thinks that when the full smelting power of the furnace is desired, the angle should not be less tlmn 

 70, which is about that of the Scotch furnaces. 



