c, the mouth of the fire-arch.
d, the santee, consisting of two stones, 3 feet long, and 3 feet 6 inches wide, with a thickness of 6 or 7 inches. They reach from the bottom of the ash-pit to a foot above the basin-stone, the interstice between them being rammed full of clay, and the whole measuring 18 inches across. (This keeps the lead, slag, &c., from running into the fire-arch, and is an important part of the furnace, requiring considerable skill and accuracy in the construction.)
e, the basin-stone, 4 feet square, and 1 foot thick.
f, the flue, or throat, 10 feet long, 22 inches wide, and 11 inches in height. This must be continued a foot and a half over the mouth of the flue, or apron, making the whole length eleven and a half feet; some prefer the flue twelve and a half feet.
g, the mouth of the flue or apron, where the furnace is charged; this flares from 22 inches to 3 feet, in a distance of 3 feet, (as shown in Fig. 3.)
h, the fire-arch, 3 feet high in the centre, 18 inches high where the arch begins to spring, and the same over the centre of the basin-stone.
Figure 3. Ground Plan.
From a to b, 8 feet; from b to c, 8 feet 6 inches; from a to d, 8 feet 6 inches; from e to f, 6 feet; from e to g, 13 feet.
h, the basin, 4 feet long, and 22 inches wide, except in the centre, where it is 24 inches wide.
i, the flue.