Mr. Scott Russell'. calculations had relation to the quantity of water and of fuel required, as well as that of the steam-pipe ; and he arrives at the conclusion 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 I. to say, at 60' in the inside of the room when the atmosphere ia 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 calculation rests on the maintenance of the required temperature so far as the room and its contents are concerned ; but the change of the air requisite for a person living in the room disturbs the formula, and brings into it many now elements.
This mode of heating buildings is adopted to a large extent in Lancashire, Yorkshire, and Cheshire, in the ateam.power factories. In the cotton.mills, woollen-mill., flax.mille, power-loom factories, dye.
-- — works, bleech-worke, print-works, &c., the facilities for producing an uninterrupted supply of steam arc so great, that the steam-heating system becomes by far the most economical that can be employed. Orrell's cotton-mill at Stockport may be taken as an exemplification of a large class of such buildings. This mill is situated on the banks of the 31ersey, and occupies a ground area of 230 feet by 200 feet. It is six stories in height, and has several distinct apartments 2S0 feet in length each. All the preparatory processes are effected In the upper stories ; while the weaving and finishing are conducted below; but all the rooms and galleries are alike boated by large steam-pipes, running the whole length of the rooms, and conveying steam from one end of the building, where the boiler. are situated, which furnish not only this supply of steam, but also that required by four steam-enginea employed in the mill. The steam is admitted to the heating-pipes in quantity proportionate to the coldness of the weather.
A very large structure at New York, presented to the city as a museum and locturo-room, and called the Union Building, affords a good example of the stcam-heating system. There are no leas than eight miles of small pipe arranged in the basement, filled with high pressure steam. A fan-blower, twelve feet in diameter, sends a vast body of air rapidly through the pipe-rooms; and the air thus warmed finds its way into spaces beneath every floor. A hole of one inch diameter is made through the floor under every chair or seat in the lecture-hall, 2300 in number ; up these holes warm air is sent in winter, and cold air in summer.
Warming by Hot Water.—The principle on which the hot-water method is founded ie different from all the others which have passed under our notice. When a vessel of water is heated, the water does not become hot by the conduction of caloric from particle to particle, but from the ascent of heated particles from the bottom, where we suppose the heating agent to be applied, to the upper strata. This is
proved from the circumstance that if heat be applied only to the surface of the water in a vessel, it is by extremely slow degrees that the lower strata becomes heated. Heat being applied to the bottom of a vessel, the lower strata of particles, becoming specifically lighter than before, ascend, while the colder particles at the surface descend to supply their place ; and hence a series of ascending and descending currents is formed. Now, if, instead of having the heated water only in a vessel, it ramify also through closed tubes connected with the vessel, the ascending and descending currents may be passed through different parts of a building, besides the room where the vessel itself may be placed. The heated water, rising to 212°, or to any temperature depending on the fire to which it is exposed, gives out heat to the metallic pipe through which it passes, and this pipe again communicates heat to the air of the room. Hence the operation of this method of warming depends on the circulating, or aseensive and deseen sive property of heated water, by which the portions of pipe farthest removed from the fire become as much heated as those in its immediate vicinity.
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 of necessity 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 (with out 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. A closed boiler is, however, more exten sively 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 circulation ensues which speedily causes the whole length of tubing to become hot. In this form of the apparatus the temperature of the water is kept down to a moderate pitch, in order to avoid danger; but in a modification of it, called the " high pressure" method, the boiler consists of a coil of pipe forming part of the circulating pipe, and is capable of being safely heated to such a degree that the pressure of the water within equals 10001ba. on the square inch. The whole system of water circulation is brought to so high a temperature, that the metal of the pipes warms the air of a largo building very speedily.