6o
MODERN STEAM PRACTICE.
have ample capacity, so that the flame hangs, as it were, beforepassing through the small tubes, giving more time to abstract theheat from the gases before they pass up the chimney. This is morerequired when the uptakes in front of the furnaces are made dry,or separate from the body of the boiler, so as to keep the stoking-room as cool as possible. For moderate power, say 300 horse-power nominal, four boilers are adopted, with uptakes arrangedfor two funnels; and should the section of the vessel be very fine,with a great rise of floor, the back end can be bevelled or cut awayat the bottom to suit the form of the ship. All the flat parts arestayed in the usual manner. For ships of war, when the stoke-hole is fore and aft, on the centre line of the vessel, the uptakesshould form part of the boiler, as dry uptakes would make it intoler-
aa, Furnaces. b, Combustion chamber. cc, Tubes. d, Smoke-box. ee, Separate uptakes. f, Chimney .
ably warm for the firemen. The uptakes, or “ lumleg,” should bemade double; they can be made slightly oval, and be strengthenedwith conical tubes, so that the steam freely passes through them;and when great steam pressure is demanded the insides and theoutsides of the uptakes should be well secured with screwed stays;this arrangement will make a very effective superheater. The topof the uptakes must be below the water line. When one funnel isrequired for six boilers, it is placed centrally between the four frontboilers, and the aft boilers have dry pipes, thus joining the threeboilers on a side; the back of the boilers at the bottom are cutaway to suit the form of the ship, but when this is not requiredthey should be straight, thus simplifying the construction. The up-takes must be fitted with the usual outer casings, for taking awaythe vitiated atmosphere from the stoking-rooms.