Many largo and important buildings are warmed on one or other of these two hot-water systems—mostly on that with the closed boiler. The hot-water apparatus put up by Mr. Perkins in the British Museum, for warming the rooms formerly used by readers, suggested the plan which is adopted for warming the present magnificent readiug-room. This room is warmed by three boilers, the furnaces of which consume their own smoke. Main pipes conduct the hot water from these boilers to smaller pipes, which bring it into the room, and the water then returns by other pipes to the same boilers. There is an air-shaft which reaches the full height of the building, having windows in it to admit fresh air. There ia a fan, or blower, at the bottom of tho shaft. Air Is forced from the shaft through valves into arched brick chambers, whence it cannot return. This air is filtered through a wire sieve, and is then conveyed up into the reading-room—not to warm it, but to keep up a supply of pure air. The doors of the room are made double, insomuch that nearly all the air that enters it comes from this shaft. There are pipes under each table, and valves above the tables to admit warm or cold air according to the season of the year. The new Houses of Parliament are also warmed by a modification of the hot-water system. .
Another large structure, the warming of which may be adduced as an example of this system, is St. George's Hall, at LiverpooL Furnaces and boilers send hot water through about a mile of 4-inch pipe. A fan, worked by a 10-horse power steam-engine, draws in the external air, and drives it past the hot-water pipes. The warmed air enters the halls and courts by apertures in the walls and floors. The temperature of the pipes rarely exceeds 90°. There are 120 fire-places and flues of various kinds; but there are no chimney-pots, and no smoke is made. There are open fire-places in many of the rooms, in which coal is used that has been partially burned, but not actually coked, previously. What little smoke there is escapes, together with the vitiated air, up flues at the four corners of the hall; these flues have curved deflectors outside, and louvres inside, to shield the ascending currents from eddies of wind. There are vast air-chambers between the ceiling of the hall and the outer roof, to carry off the respired air and the products of the combustion of the gas lights.
Vs/tab:rasa—There is an important, but often neglected circum stance attending the artifical warming of buildings : namely, that the amount of fresh air, requisite under any condition for animal res piration, 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. Now,
under the 'common arrangements of an English apartment, the open fire-place and the tall chimney draw air so rapidly in that direction, that the whole body of air in the room becomes speedily changed, pro vided there be an average amount of open doors, windows, crevices, &c. to yield the supply. Until modern inquirers set themselves to solve these two questions, or others analogous to them—" How many cubic feet of air are requisite for the combustion of a pound of coal !" and, " How many cubic feet of air are respired by an average man in an hour r—there were no means of determining the proper amount of air necessary to be supplied in a building where close stoves are used, or where the methods of warming by heated air, by steam, or by hot water are adopted.
Dr. Arnett places the matter under the following form, so far as respiration alone is concerned :—" In respiration or breathing a man draws into his chest at one time about twenty cubic inches of air, and of that air a fifth part is oxygen ; of which again there is converted into carbonic acid gas nearly a half. The carbonic acid, if afterwards inhaled, would be noxious to the individual. About fifteen inspira tions are made in a minute, vitiating, therefore, three hundred cubic inches, or nearly one-sixth of a cubic foot, of atmospheric air, but which, mixing as it escapes with several times as much, renders unfit for respiration at least two cubic feet under common circumstances." Tredgold makes a very different estimate of the quantity of air respired in a minuta, and introduces other items into his calculations. In the first place he reckons the average number of respirations per minute twenty, and the number of cubic inches of air inspired each time forty ; so that the air directly vitiated amounts to eight hundred cubic inches per minute. He next takes into consideration the vapour mixed with the respired air, and the insensible perspiration alwaye going on from the skin, and assumes that three cubic feet of air per minute will be requisite to remove these causes of impurity. Lastly, he supposes a room to contain persons in the evening, when candles, lamps, &c. are lighted, and in lieu of the air vitiated by this combus tion he assumes (on what data does not clearly appear) that one-fourth of a cubio foot of fresh air per minute for every individual will be necessary to purify the atmosphere of the room on this ground. Taking all these results together, Tredgold comes to the conclusion, that when a room containing several persons is lighted 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.