Close Stoves.
In a close stove, no air is admitted but what passes at once through the fire; and the chimney or funnel is only just large enough to carry off the sulphurous and other vapours, for there is hardly any smoke from a close stove, and, therefore, it is not necessary to make a chimney large enough to admit a climbing-boy.
A small German stove, suitable for a room twenty-four feet by eighteen, will give an idea of the general character of this kind of close stove. The stove rests on a base about thirty-six inches by fourteen. The fire-place has a bottom to receive the fuel, but no bars, and is shut by a door which fits closely to its case. This door has a small wicket at the bottom, the aperture of which is regulated by a sliding plate, so as to admit no more air than will suffice for the slow combustion of the fuel. The flame and heated air ascend to the top of the fire-place, and pass into two hollow pillars or piers, which rise to a height of five or six feet, so that the heat is communicated to a large surface, before the volatilized products of combustion make their exit by a pipe into the chimney. The stove is supplied with fuel and with air by the front door. If it is desired to make the fire visible, and impart some of that cheerfulness which belongs to an open grate, the door of the stove maybe thrown open, for there is no danger of the smoke coming out after the current has once warmed the upper part of the stove. When the stove is of such dimensions that the body of it is about two feet and a half high, the fire-place may be furnished with a small grate in the English style. If the door is so hung that it can not only be thrown back, but also lifted off its hinges, it will approach still more to the character of a stove-grate.
A cheap form of “German stove” is often made in this country, and used in workshops and small manufactories, where the body of the stove is an upright cylinder, of which the lower part is the ash-pit, closed or opened by a hinged-door, the middle part the fire-place, where the fuel rests on bars, and the upper part a vacant space, which becomes filled with flame, smoke, and heated air, so as to impart great heat to a flat iron plate at the top. There is a door at which the fuel is introduced, and a small flue or funnel of iron pipe, which conveys the smoke into a chimney or into the open air. Many forms of stove have been used more or less resembling this in principle; but there is one great defect pertaining to them all. The metal of which the stove is formed becomes so highly heated near the stove, that it acquires a burnt smell, owing to the decomposition of animal and vegetable particles which are at all times floating about in the air. The air, too, in the room, becomes close and oppressive from another cause; for as only a small quantity of air is consumed by the stove, the air does not become renewed in the room so frequently as when an open fire is used, and thus it is respired over and over again.
To remedy the evils resulting from burnt air, close stoves are made with a double case, so that there shall be a body of air between the fire and the air of the room. It is on this principle, modified in various ways, that a large number of stoves have been constructed; of which one, by Mr. Sylvester, may be briefly described. There is a hollow cast-iron box, on the outside of which are cast several ribs. Those ribs are about three-quarters of an inch thick, and project three or four inches beyond the surface of the box; and their object is to increase the heating surface; for the fire being lighted in the hollow of the box, the conducting power of the iron causes the whole exterior case of the box, together with the projecting ribs, to become heated. The box is placed within an ornamental case, the sides and top of which are fretted with lattice-work, to allow free access to the air, which enters through the lattices at the sides and escapes from the top of the stove, passing in its passage over the ribbed surface of the heated box. The grating on which the fuel lies is formed of a number of loose bars fitted together into a frame, and prolonged so as to emit heat into the room as well as to support the fuel. Everything is so arranged as to give as much iron surface as possible, so as to communicate heat to the surrounding air; while at the same time the extent of the heated surface prevents any one part from being excessively and injuriously heated.
Dr. Arnott’s Stove.
To describe all the “chunk” stoves, “Vesta” stoves, “Olmsted” stoves, and other similar contrivances of modern times, would fill a volume instead of a few pages. We may, however, speak briefly of Dr. Arnott’s stoves as a means of showing some of the inconveniences to which close stoves are liable, if not constructed with care. This stove consists of an external case of iron, of any ornamental shape. Within this case is placed a box made of fire-clay, to contain the fuel, having a grating at the bottom; and there is a space left between the fire-box and the exterior case, to prevent the communication of too much heat to the latter. Thee pedestal of the stove forms the ash-pit; and there is no communication between the stove and the ash-pit, except through the grating at the bottom of the fire-box. A small external hole in the ash-pit, covered by a valve, admits the air to the fire; and according as this valve is more or less open, the vividness of the combustion is increased or diminished, and thence the greater or less heat produced by the stove. The quantity of air admitted by this valve is governed by a self-regulating apparatus, either by the expansion and contraction of air confined by mercury in a tube, or by the unequal expansion of different metals. The smoke escapes through a pipe at the back of the stove; but the fuel employed is such as to yield very little smoke. By adjusting the regulator so as to admit only a small quantity or air, the temperature of the stove is kept within the required limits; and owing to the slow-conducting power of the fire-clay, of which the fire-box is formed, the heat of the fuel is concentrated within the fire-box, and the fuel burns with less air and less rapidity than it would otherwise do.
The construction of Dr. Arnott’s “thermometer stove” will be better understood from the following figure, which represents the stove with one of its sides removed, so as to exhibit its interior arrangements:—
The outlines of the figure, a a a a, represent the case or body of the stove, which might be formed either of cast or sheet iron. It is divided into two chambers by the partition, b b; but in such a way that there may be a free communication at the top and bottom. c is a small furnace, or, as it is called by the inventor, a fire-box, made of iron, and lined with fire-bricks. The fire-box is not in contact with the exterior case of the stove. It communicates at the bottom with an ash-pit, the door of which is at d,—that of the stove, by which the fuel is introduced, is at d´. Both these doors must fit very accurately. Above the door of the ash-pit is a bent pipe e, by which air gains admittance to the fire.
A fire being kindled and the doors at d d´ shut, the only way in which air has access to the fuel is by the pipe e; the air so admitted, passing through the fire before it enters the upper part of the stove. That portion of the air not required to aid the combustion of the fuel having reached the main body of the stove, and there mixing with the smoke and other products, they circulate slowly in the directions indicated by the arrows, and at length pass into the chimney by the pipe f.
The slow movement just mentioned as taking place within the stove may well be contrasted with what happens in an open fire-place. In one case the greater part of the heat produced is rapidly carried off by a current of air ascending the chimney—by the thermometer stove it is detained until almost the whole of it has been diffused throughout the apartment.
The bent tube g terminating in a cup-shaped opening at g´, is a self-regulating valve. The tube is closed at the end g within the stove, g´ g´´ represents mercury which occupies the bend of the tube. When the fire in the stove burns too briskly, the air in the tube occupying the space between g and g´´ is expanded, and by expelling some of the mercury from the tube at g´´ into the cup at g´, it closes the aperture of the pipe e; thus cutting off the supply of air to the fire. In a few minutes (the fire in the mean time having abated its energy,) the air in the tube will return to its former dimensions, and the mercury subsiding in the cup, air is again permitted to enter the ash-pit.
The stove, of which we have thus attempted to convey a general idea, may be made of any required form or size. Instead of the self-regulating air-valve just described, it is fitted up with others of a very simple construction, and which admit of being adjusted with the greatest accuracy by the hand.
The objections to this form of stove arise chiefly from the formation of deleterious gases, which are not carried off completely. The slow combustion of the fuel produces a large quantity of carbonic oxide, which is liable to escape into the room, and is of an injurious character. Carburetted hydrogen gas is also formed in these stoves. Many modifications of form have been suggested for the remedy of these evils; but the slow combustion, which was one of the merits originally claimed for the stove, and which it certainly deserves, seems an unavoidable cause for the production of these gases.
All the varieties of open fire-place, as adopted in English houses, the hearth, the recess, and the chimney, are at one side or at one corner of the room; but in the adoption of close stoves this arrangement is not necessary; for the stove may be in any part of the middle of a room, provided the pipe constituting the flue be long enough. In some cases this pipe is carried upwards to the ceiling, and thence conveyed to some outlet into the open air; in other cases it is turned downwards and conveyed under the flooring to a proper place of exit; while in others the pipe is stretched or extended horizontally from the stove to the regular chimney of the room.