MODERN STEAM PRACTICE.

to the action of the flame; the bottom joints are embedded inthe brickwork, and each of the tubes exposes an area of 16 feet,

a, Shell, b, Fire-box. c, Smoke-pipe. D, Circulating waterspace. e, Conical tubes. f, Fire-door. g, Sludge cap

Fig. 15.—Water-tube Boiler, a, Furnace. b, Tubes. c, Flue.d d, Division plates. e, Damper. f, Stop valve. G, Chimney .

J ‘ Fig. 16.—Self-contained Water-

so manufactured that no destructive ex- tube Boiler,

pansion may be allowed to take place, and all the joints should bemetal to metal where practicable.

Water-tube boilers, sometimes called tubulous, may be of variousforms. The water tubes can be arranged in a variety of ways,so that the furnaces, the tubes, and the shell are self-contained.Thus to an ordinary vertical boiler an inside fire-box is fitted, aslikewise a pot-shaped vessel connected by circulating pipes with theshell, as shown by Figs. 15 and 16. A current of water is continually

descending between the fire-box and the outside shell, and finds itsway into the pot through the circulating pipes at the bottom. Theseboilers keep free from deposit, owing to the rapid circulation, andfor some purposes are recommended to be arranged with conical orcommon tubes.