Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 2, 1802).djvu/323

291&#93; F I P. Is raised or depressed by rheai tu'd ln.i>s knobs, and it slides in a I between the foremost . of the side-plates and the face of the front plate. i r, which is pUtct d between the back plate and air- box, and is furnished with a key ; so that it m.iv be turned on its axis, and raised or lowered at pleasure in an oblique position. The opera- tion of this machine, and the me- thod of lixing it, may he understood by attentively observing the profile of the chimney and fire-places in the following figure. Fi R [2?t M is the mantle-piece, or breast of the chimney ; C the funnel ; B the false back, made of brick- work within the chimney, at the distance of four inches from t!ie true back, or upwards, from the top of which a closing is to be made over to the breast of the chimney ; in order that no air may enter except that which passes un- der the false back, a: d ascends be- hind it. E is the true back of the chimney ; T. the top of the fire- place ; F the front of it ; A the place where the fire is made j D ilr-box, K the bole in thei side plate, throbgh which th* warmed air is discharged from the air-box into the room. H is the hollow formed by removing some bricks from the hearth under the bottom plate, filled with fresh air, which enters At the passage I, and ascends i:ito the box through the air-hole in the bottom plate near G, the partition of the hollow, and which is designed to separate the air and smoke. — P, is the passage under the false back, and part of the hearth for the smoke, the course of which is pointed out by the ar- rows delineated in the last figure. The fire is to be made at A, when the flame and smoke will ascend j strike the top T, and communi- cate to it a considerable degree of heat ; the smoke will turn over the air-box, descend between it and the back-plate to the holes n°ar G in t e bottom plate ; and heating in its passage all the plates of the machine, it will then proceed un- der and behind the false back, whence it will rise into the chim- ney. The air of the apartment contiguous to the several plates. and warmed by them, become spe- cifically lighter than the other a.r in the room, and is compelled to rise ; but, being prevented by the closure over the fire-place, it is? forced out into the room ; and ascending by the mantle-piece to the ceiling, is again gradually driven down by the stream of new- ly warmed air which follows ; so that the whole room in a short time acquires an ecmal tempera- ture. The air a!so that is warmed beneath the bottom plate, and in the air-box, rises out of the holes in the side plates, and thus warms, and continually changes that of the room. U 2 H