118 
Iron. 
face of the piston. The area of each is proportioned to 
the number of valves : commonly they are 12 to 16 inch- 
es.— G, a pile of solid stone building, on which the re- 
gulating cylinder rests, and to which the Ranch and tilts 
of the blowing cylinder are attached.- — H, the safety-valve, 
or cock : by the simple turning of which the blast may 
be admitted to, or shut off from the furnace, and passed 
off to a collateral tube on the opposite side. — I, the tuyere, 
by which the blast enters the fa mace* The end of the 
tapered pipe, which approaches the tuyere, receives small 
pipes of various diameters, from two to three inches, call- 
ed nose pipes . These are applied at pleasure, and as the 
strength and velocity of the blast may require.— K, the 
bottom of the hearth, two feet square.— L, the top of the 
hearth, two feet six inches square.— KL, the height of the 
hearth, six feet six inches.— L, is also the bottom of the 
boshes, which here terminate of the same size as the top 
of the hearth ; only the former are round, and the later 
square.— M, the top of the boshes, 12 feet diameter and 
eight feet of perpendicular height.— N, the top of the fur- 
nace, at which the materials are charged ; commonly three 
feet diameter.— MN, the internal cavity of the furnace 
from the top of the boshes upwards, 30 feet high. — -NK, 
total height of the internal parts of the furnace, 44 1-2 feet, 
p — GO, the lining. This is done in the nicest manner 
with fire-bricks made on purpose, 13 inches long and 
three inches thick.— PP, a vacancy which is left all round 
the outside of the first lining, three inches broad, and 
which is beat full of coak-dust. This space is allowed 
for any expansion which might take place in consequence 
of the swelling of the materials by heat when descending 
to the bottom of the furnace.— QQ, the second lining, si- 
milar to the first.— R, a cast iron lintel, on which the bot- 
tom of the arch is supported.— RS, the rise of the arch.— 
ST, height of the arch ; on the outside 14 feet, and IS 
