119 
Iron • 
fet wide.— VV, the extremes of the hearth, ten feet 
square. This and the bosh stones are always made from 
a coarse gritted freestone, whose fracture presents large 
rounded grains of quartz, connected by means of a ce- 
ment less pure. 
Figure 2 represents the foundation of the furnace, and 
a full view of the manner in which the false bottom is con- 
structed. 
AA, the bottom stones of the hearth. B, stratum of 
bedding sand. CC, passages by which the vapour, 
which may be generated from the damps, are passed off , 
DD, pillars of brick. The letters in the horizontal view* 
of the same figure, correspond to similar letters in the dot- 
ted elevation. 
Figure 3, A A, horizontal section of the diameter of 
the boshes, the lining and vacancy for stuffing at M. C, 
view of the top of the hearth at L. 
Figure 4, vertical side- section of the hearth and boshes ;■ 
shewing the tymp and dam-stones, and the tymp dam- 
plates. a, the tymp-stone. the tymp-plate, which is 
wedged firmly to the stone, to keep it firm in case of split- 
ting by the great heat.— c, dam-stone, which occupies the 
whole breadth of the bottom of the hearth, excepting about 
six inches, which, when the furnace is at work is filled 
every cast with strong sand. This stone is surmounted 
by an iron plate of considerable thickness, and of a pecu- 
liar shape, d, and from this called the dam-plate. The 
top of the dam-stone and plate is two, three, or four inches 
under the level of the tuyere hole. The space betwixt 
the bottom of the tymp and the dotted line is also rammed 
full of strong sand, and sometimes fire-clay. This is called 
the tymp- stopping, and prevents any part of the blast 
from being unnecessarily expended. 
The square of the base of this blast-furnace is 38 feet; 
the extreme height from the false bottom to the top of the 
crater is 55 feet. 
