WARMING AND VENTILATION. Under the headings ARNOTT'S STOVE, COOKING APPARATUS, and STOVE, descriptions are given of various grates, stoves, and fire-places; other modes of warming buildings call for a little notice here.
The employment of steam-boilers in large establishments where steam-engines are worked, is one of the circumstances which have led to the very extensive adoption of the method of warming by steam. A marked lifference is observable in the principle of this method, as compared with that of hot fir warming. The steam is not permitted to mingle with the air of the room which is to be warmed, but acts through the medium of the metallic tube which confines it, and which it raises to a temperature sufficient to warm the room. The efficacy of this mode of heating depends on the great capacity for heat which steam possesses, a capacity equal to 1000° ; that is, a pound of water at 212° will absorb a thousand degrees of heat in becoming a pound of steam. Mr. Scott Russell calcu lates that a room containing 500 cubic feet of air, and exposing 400 feet of surface, may be maintained at a temperature of 20° above that of the air without—that is to say, at 00° in the inside of the room when the atmos phere is at 40° without—for a space of twelve hours, by the evaporation of two gallons of water, and at the expense of about three pounds of coal. This mode of heating buildings is adopted to a very large extent in the steam-power factories.
The method of heating by hot water, though not so much adopted in factories as the steam method, is perhaps of more ex tensive application in other buildings. Where all the apartments to be warmed are on one level, an open boiler may be used ; but where it is necessary to carry the pipes to different floors of a building, some of them much above the level of the boiler, the boiler must in that case be closed. When an open boiler is employed, a pipe branches out from the upper part of the side, extends horizontally through the rooms to be warmed (without in any case rising above the level of the water in the boiler), and returns again to the boiler, which it enters at a lower level than the other, Under this arrangement a current of heated water will flow from the boiler at the upper orifice, and, after traversing the tube, return to the lower orifice. The closed boiler is however more extensively useful, since it enables all the stories of a building to be warmed by one apparatus. The whole system, including both tubes and boiler, is filled with water at a valve at the highest point; and when heat is applied to the boiler, a circu lation ensues which speedily causes the whole length of tubing to become hot. Various modifications of this hot-water system are adopted in the new Houses of Parliament, in the British Museum, and other public buildings.
Ventilation.—There is an important but often neglected circumstance attending the artificial warming of buildings, viz. that the amount of fresh air, requisite under any condition for animal respiration, must be more and more increased in proportion to the fuel burned in the room ; or, more correctly, there must be one portion of air to feed combustion, and another portion to aid respiration.
Tredgold, Arnett, Reid, and others, have cal culated the quantity of air required for these purposes. Tredgold states that when a room containing several persons is heated to the average and customary degree, it will be necessary to supply four times as many cubic, feet of fresh. air per minute, as there are persons in the room ; that is, four feet for each person. But there must be an outlet for the vitiated air equal to the inlet for pure air ; and as it is found that respired air ascends to the upper part of the room, it follows that the ceiling or some neighbouring part is the proper place for an outlet.
In ordinary English houses no steps what. ever are taken to regulate either the supply of pure air or the exit of vitiated air ; but it is probable that our large fire-places regulate this matter tolerably well. In crowded rooms however, where the amount of vitiated breath bears a much larger ratio to the cubical con tents, and where the doors are generally small compared with the height of the room, the impure air cannot escape by these means, and some arrangements must be made near the ceiling for the removal of the air. These methods are chiefly of two different kinds; the one by the use of a revolving wheel or fan-ventilator, and the other by the action of a chimney or tube. At the Reform Club House, London, a steam-engine works a revolving fan, capable of throwing eleven thousand cubic feet of air per minute into a subterranean tunnel under the basement story; and the steam from the small steam-enginel which works the fan supplies three cast-iron chests with the requisite heat for warming the whole building.
The second mode of effecting ventilation, viz. by the use of a tube or chimney opening into the air from the upper part of an apart ment, depends for its action on the ascensive power possessed by a lofty aerial column. As the heated air of a furnace-chimney carries up the smoke, &c., more rapidly if the chimney he very lofty, so does a lofty chimney exceed a low one in carrying off vitiated air ; and for the same reason, even if no chimney, properly so called, be provided, a lofty room, furnished with appropriate openings in its ceiling, will furnish a draught to carry off impure air more rapidly than a low room ; and in many of our public buildings this arrangement is deemed sufficient.
Dr. Arnett has made use of the ascending force of the column of heated air in an ordi nary chimney as a means of ventilating ordinary sitting rooms, by placing a balanced valve in an opening from the room into the chimney. He has also introduced very re cently a mode of ventilating large buildings by applying the pressure of a column of water to work a forcing air-pump. These admirable contrivances, so worthy of the accomplished physician to whom they are due, are noticed under ARNOTT'S VENTILATOR. Many forms of ship-ventilation depend on the use of an air-pump.