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shoulder for it to rest on; also two pair of ledges to receive the side edges of the two middle plates, which form the air-box; and an oblong air-hole near the top, through which is discharged into the room the air warmed in the air-box. Each has also a wing or bracket, H and I, to keep in falling brands, coals, &c., and a small hole, Q and R, for the axis of the register to turn in.
(iv, iv) The air-box is composed of the two middle plates, D, E and F, G. The first has five thin ledges. or partitions cast on it, two inches deep, the edges of which are received in so many pair of ledges cast in the other. The tops of all the cavities formed by these thin, deep ledges, are also covered by a ledge of the same form and depth, cast with them; so that when the plates are put together, and the joints luted, there is no communication between the air-box and the smoke. In the winding passages of this box, fresh air is warmed as it passes into the room.
(v) The front plate is arched on the under side, and ornamented with foliages, &c.; it has no ledges.
(vi) The top plate has a pair of ears, M, N, answerable to those in the bottom plate, and perforated for the same purpose; it has also a pair of ledges running round the under side, to receive the top edges of the front, back, and side plates. The air-box does not reach up to the top plate by two inches and a half.
(vii) The shutter is of thin wrought iron and light, of such a length and breadth as to close well the opening of the fire-place. It is used to blow up the fire, and to shut up and secure it at nights. It has two brass knobs for handles, d, d, and commonly slides up and down in a groove, left, in putting up the fire-place, between the foremost ledge of the side plates, and the face of the front plate; but some choose to set it aside when it is not in use, and apply it on occasion.
(viii) The register is also of thin wrought iron. It is placed between the back plate and air-box, and can, by means of the key S, be turned on its axis so as to lie in any position between level and upright.
The screw-rods, O, P, are of wrought iron, about a third of an inch thick, with a button at bottom, and a screw and nut at top, and may be ornamented with two small brasses screwed on above the nuts.
To put this machine to work,
1. A false back of four-inch (or, in shallow small chimneys, two-inch) brick work is to be made in the chimney, four inches or more from the true back; from the top of this false back a closing is to be made over to the breast of the chimney, that no air may pass into the chimney, but what goes under the false back, and up behind it.
2. Some bricks of the hearth are to be taken up, to form a hollow under the bottom plate; across which hollow runs a thin, tight partition, to keep apart the air entering the hollow and the smoke; and is therefore placed between the air-hole and smoke-holes.
3. A passage is made, communicating with the outward air, to introduce that air into the fore part of the hollow under the bottom plate, whence it may rise through the air-hole into the air-box.
4. A passage is made from the back part of the hollow, communicating with the flue behind the false back; through this passage the smoke is to pass.
The fire-place is to be erected upon these hollows, by putting all the plates in their places, and screwing them together.
Its operation may be conceived by observing the plate entitled, Profile of the Chimney and Fire-place (See Plate VI.)
M The inantel-piece, or breast of the chimney.
B The false back and closing.
E True back of the chimney.
F The front of it.
A The place where the fire is made.
K The hole in the side plate, through which the warmed air is discharged out of the air-box into the
H The hollow filled with fresh air, entering at the passage I, and ascending into the air-box through the air-hole in the bottom plate, near
G The partition in the hollow to keep the air and smoke apart.
P The passage under the false back and part of the hearth for the smoke.
The arrows show the course of the smoke.
The fire being made at A, the flame and smoke will ascend and strike the top T, which will thereby receive a considerable heat. The smoke, finding no passage upwards, turns over the top of the air-box, and descends between it and the back plate to the holes in the bottom plate, heating, as it passes, both plates of the air-box, and the said back plate; the front plate, bottom and side plates are also all heated at the same time. The smoke proceeds in the passage that leads it under and behind the false back, and so rises into the chimney. The air of the room, warmed behind the back plate, and by the sides, front, and top plates, becoming specifically lighter than the other air in the room, is obliged to rise; but the closure over the fireplace hindering it from going up the chimney, it is forced out into the room, rises by the mantel-piece to the ceiling, and spreads all over the top of the room, whence being crowded down gradually by the stream