Fire-Box

That part of an internally fired boiler in which the combustion of the fuel takes place. The sheet over the fire is called the crown-sheet; that to which the fire-tubes are secured is called the tube-sheet. At the sides of the fire-box are the water legs, two parallel sheets of plate tied together by stay-bolts. At the bottom of the water legs is the mudring. The crown-sheet is held from collapse by the crown-bars or by stays (see BELPAIRE FIRE-BOX); the opening for the fire do or through the water leg is made water-tight by a flanged or forged ring. Many fire-boxes have a bridge wall acro them, to make a combustion chamber. Fire-boxes for anthracite coal are made larger than for bituminous, since the former acts more by radiation from the incandescent bed of fuel. For burning fine coal, and slack or culm, the area must be made very large, so as to secure slow rates of combustion. In earlier locomotives the fire-box was put between the frames; in many recent designs the fire-box is over the frames, and much greater area is po ible. The Wootten fire-box is of this cla . See WOOTTEN.