ON THE CONSTRUCTION AND HEATING OF HOT-HOUSES. 
251 
same general principle is followed as in that already described ; but the boiler and 
the furnace are so formed that a smaller quantity of water is contained between them 
compared with the surface exposed to the heat from the fire, and the arrangement 
of the parts is better calculated to promote a rapid circulation of the water in the 
Fig. 3. 
pipes. For this purpose the cylinder L, instead of being placed at the same end of 
the boiler as the pipes, is removed to the opposite end, and the upper end is con- 
nected with it ; consequently the water enters from the lower pipe at one exti emity 
of the boiler, passes through its whole length over the surfaces of the furnace and 
flue, becoming gradually heated in its passage, and then rises through the cylinder 
into the upper pipe, thus flowing in a constant and regular current through the 
whole apparatus. 
In figure 3, the front of the fire-place, where ignited fuel would be inconvenient, 
is occupied by a large fire-tile^ P, on which a supply of fuel may be heated previous 
to its being pushed forward on the grate. Q is a bridge formed of fire clay in one 
piece, which may be removed when the flue requires cleaning. The flue, instead of 
passing through the top of the boiler, is brought out at the front, where it turns 
upwards, and is intended to be carried into a common chimney. Thus the furnace 
and flue being fixed only to the front, and unconnected with any other part of the 
boiler, the whole may be removed in a few minutes, should any repair be necessary. 
The furnace in figure 3, though well adapted for burning coke, cinders, or dry 
wood, would perhaps not answer well for coal, as the smoke would be so much 
chilled by contact with the metallic surface of the fire-place, that the flue would be 
liable to become foul. This might be prevented by constructing the furnace as in 
figure 4, lining it throughout with fire brick. S is an inclined plane of fire-tiles, 
on which the fuel is to be spread when first put into the furnace. At T T are air 
passages, between the fire bricks and the case of the furnace, leading from the front, 
and having openings, U U, into the fire-place at the joints of the bricks above the 
inclined plane. A regulated supply of air being admitted through these openings 
would mix with the vapours rising from the coal, and in a great measure effect th© 
