currents may not interfere with each other.
In blast and cupola furnaces, but especially the latter, a number of tuyeres have been employed, arranged in vertical series, as shown in Fig. 6826. See also cupola-furnace.
In Fig. 6826, the area of the blast openings of the tuyeres decreases toward the upper portion of the series, and their mouths are protected by pillars of fire-brick.
Pevy's cupola-furnace has a wind-chest around the furnace, from whence the tuyeres are supplied.
Truesdale's cupola-furnace has circular rows of tuyeres around the chamber, arranged in several tiers.
The blastopen-ings decrease in area in the several tiers from the upper to the lower.
The tuyeres of the Bessemer convertor are perforated blocks of fire-brick set in the floor of the retort, and affording passage for the air into the mass of liquid metal above.
See Bessemer; convertor; steel.
The blast-pipe of the forge or furnace is sometimes cooled by passing through a casing around whi