A top plate (vi)
These are all cast of iron, with mouldings or ledges where the plates 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 Fig. 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 Fig. 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 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 chuse to set it aside when it is not in use, and apply it on occasion.