17 
Steam Engine* 
adviseable to give it less or more opening according to the 
state of the fire, that is, when coals are newly introduced 
into the fire-place, to give the greatest quantity of fresh 
air, and when they are pretty well kindled to give less 
air. F F F, Fig. 7, the flues beneath and round the boil- 
er ; that round the boiler, may be in any of the present 
well- constructed forms ; that beneath the boiler, as in the 
drawing with a breast D, to prevent the coal getting so far 
backward in the furnace, and also to direct the flame on 
the bottom of the boiler : this breast is also necessary for 
the more complete combustion of the smoke, as by that 
means, the fresh air, smoke, and flame are more complete- 
ly combined than if the breast were wanting, or ilLformed ; 
at r is represented a shutter, which is sometimes used in 
steam engine boilers for the purpose of getting the refuse 
of the fuel taken from the furnace by opening the said 
shutter ; in other cases, the breast of the furnace D coin-- 
cides with d at the ends of the bars. ' G, Figs. 7 and 8, 
the grated-doors, or opening into the fire-place ; I, the 
ash-pit below the furnace ; L, Fig. 8, a catch, or bar, 
which slides along the bottom plate of the hopper, for 
keeping the grated-doors shut ; PI H H, &c. the brick- 
work for furnace and boiler. K, Fig. 7, a piece of cast- 
iron in a horizontal position, v/hich joins the under plate 
of the hopper, for the more ease and conveniaice in put- 
ting in the coals, the hopper may be made in one or more 
pieces, as inclination or choice may direct, or of any mate- 
rials which it may be thought prudent to adopt, but they 
are usually made with five plates of cast-iron ; M repre- 
senting one of the side plates, N the uppermost, O the lin^ 
dermost, and P the regulating-plate ; the side plates hav- 
ing tenons which fit into mortices in the top and bottom 
plate, which may easily be conceived ; on the side plates 
are detents or abutments, which serve as a centre for the re- 
gulating-plate to turn upon ; on this plate are also two 
Vol. II. C 
