The Works of Benjamin Franklin, Volume 2. Бенджамин ФранклинЧитать онлайн книгу.
come together, to hold them fast and retain the mortar used for pointing to make tight joints. When the plates are all in their places a pair of slender rods, with screws, are sufficient to bind the whole very firmly together, as it appears in Figure 2.
There are, moreover, two thin plates of wrought iron, viz., the shutter (vii.), and the register (viii.), besides the screw-rods, O, P, all which we shall explain in their order.
(i.) The bottom plate or hearth-piece is round before, with a rising moulding that serves as a fender to keep coals and ashes from coming to the floor, &c. It has two ears F, G, perforated to receive the screw-rods O, P; a long air-hole a a, through which the fresh outward air passes up into the air-box; and three smoke-holes B, C, through which the smoke descends and passes away, all represented by dark squares. It has also double ledges to receive between them the bottom edges of the back plate, the two side plates, and the two middle plates. These ledges are about an inch asunder and about half an inch high; a profile of two of them, joined to a fragment of plate, appears in Figure 3.
(ii.) The back plate is without holes, having only a pair of ledges on each side to receive the back edges of the two
(iii., iii.) Side plates; these have each a pair of ledges to receive the side edges of the front plate, and a little 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 have 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 II.)
M The mantel-piece, or breast of the chimney.
PROFILE OF THE PENNSYLVANIA CHIMNEY AND FIRE-PLACE.
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