Page:The American Cyclopædia (1879) Volume XVI.djvu/475

 WARMING AND VENTILATION 455 contact with the largest possible absorbing and radiating metallic surface, so that the iron will give out its warmth at a low temperature. But the ventilation afforded by stoves, unless especially provided for by connected warm-air chambers, is very imperfect ; only the small amount of air which is necessary for combus- tion is removed from the apartment, while they unquestionably exert a more or less dele- terious action upon the remaining air when made very hot. Precisely what the effect of red-hot iron is upon air or persons is not yet determined. The statement that it burns the oxygen out of the air is erroneous, as this effect is quite trivial. A stove weighing 84 Ibs. and kept exposed to the air at a red heat for 300 days would, if completely burned up, consume the oxygen of but 6 cub. ft. of air per day, and it would require 19 such red-hot stoves to burn the air as fast as one pair of human lungs. But the ordinary air is contaminated by a great variety of organic matters, carbon particles, filaments of cotton and wool, starch grains, vegetable spores, pollen, volatile emanations, germs of vibriones, bacterise, and monads, and floating particles of decayed tissues, such as epithelium and pus cells. As Prof. Tyndall has shown, when an electric beam passes through the air it is seen to be loaded with impalpable dirt. Inhabited apartments are charged with this organic dust, and when it comes into contact with hot iron it is decom- posed, giving rise probably to the peculiar odor of " burnt air." The old English cockle stove, introduced by Mr. Strutt toward the close of the last century, warmed houses by the distri- bution of heated air, and was the progenitor of our hot-air furnaces. It consisted of a cy- lindrical fire chamber with a dome -shaped head, and was placed in a bed of masonry with a grating and ash pit below. This part, which from its shape was called the cockle, was en- closed at a little distance by a concentric wall of brickwork, the interval forming a hot-air space. Air introduced from without was thrown into this space against the surface of the iron chamber, and, being heated and rare- fied, ascended through openings and was con- veyed to the rooms required to be warmed. The modern hot-air furnace consists of an iron stove, which may be variously shaped, and which is surrounded either by an iron or a brickwork case, with a hot-air chamber be- tween. It is situated either in the basement, cellar, or subcellar, while air brought from without (or too commonly from the subterra- nean apartments) is introduced through prop- er openings, heated, and conveyed by flues to the different apartments through registers at the base or ceiling. It is urged in behalf of hot-air furnaces that they are out of the way and save space ; that they are cleanly, and give but little trouble in attendance ; that they are economical in first cost and in consumption of fuel; that they warm the whole house or such parts of it as may at any time be desired ; and finally, that they afford at any time an abun- dant supply of warm fresh air for ventilation. On the other hand, it is objected that " furnace heat 1 ' is in a high degree unwholesome, the hot parching air being unfit for respiration; that deleterious gases escape through the open- ings of the joints, and even pass through the red-hot metal and are thrown into the stream of air to be breathed ; that sparks of fire are thus often carried through the building with the greatest danger of conflagration. But it must be admitted that the evils of hot-air furnaces are chiefly those of faulty construction and of gross mismanagement, as they have been employed for years in many dwellings with entire satis- faction. Much alarm has been created by the French experiments of Deville, Troost, and Morin (1863-'9), proving that carbonic oxide permeates cast iron when heated to redness. It has been also shown that red-hot wrought iron is penetrable in the same way. But although carbonic oxide is a far more poison- ous compound than carbonic acid, the amount of it that can permeate a red-hot plate of iron half an inch thick is so very minute that it is not to be brought into comparison with other causes of air contamination. The difficulty with cast-iron furnaces is the liability to flaws in the metal, by which obscure passages are left for the escape of gases, and the great dan- ger of leakage at the joints. This is obviated by using wrought iron for construction, and where cast iron is employed it should be tested for flaws, and the smallest number of pieces possible should be used. The attempt. to do a large amount of heating with small, cheap, lightly constructed furnaces, put up by inex- perienced men, which leads to overheating of surfaces and derangement of the structure, is a chief cause of the bad working of hot-air fur- naces. They ought to be large and thoroughly made, and placed as near the centre of the house and as low as practicable. The lower the furnace, the greater the possible inclination of the distributing air tubes, and the greater the ascensive force of the air currents. The passages for the entrance of fresh air should be ample, and every precaution should be taken that there are no causes of impurity in the neighborhood of the source of its supply. It has been pointed out how the capacity of air for moisture increases with its temperature. To prevent the parching influence of furnace- heated air, it is necessary to supply the requisite moisture by evaporation in the hot-air cham- ber. Provisions for this purpose are usually very inadequate. A copper vessel of from 2 to 4 sq. ft. of open water surface should be provided. Ruttan's air wanner seems to com- bine the better qualities of stoves and furnaces. It consists of one stove enclosed within another, with sufficient space between to admit a large amount of air, which is brought from without, enters below the floor, passes between the two stoves, and is thrown into the room above. Instead of heating a small quantity of air to a