513. _In the construction of every inhabited room, there should be adequate means of ventilation, as well as warming._ No room is well ventilated, unless as much pure air is brought into it as the occupants vitiate at every respiration. This can be effected by making an aperture in the ceiling of the room, or by constructing a ventilating flue in the chimney. This should be in contact with the flues for the escape of smoke, but separated from them by a thin brick partition. The hot air in the smoke flues will warm the separating brick partition, and consequently rarefy the air in the ventilating flue. Communication from every room in a house should be had to such flues. The draught of air can be regulated by well-adjusted registers, which in large rooms should be placed near the floor as well as near the ceiling. 514. While provision is made for the escape of rarefied impure air, we should also provide means by which pure air may be constantly admitted into the room, as the crevices of the doors and windows are not always sufficient; and, if they should be adequate, air can be introduced in a more convenient, economical, and appropriate manner. There should be an aperture opposite the ventilating flue, at or near the floor, to connect with the outer walls of the building or external air. But if pure heated air is introduced into the room, it obviates the necessity of the introduction of the external air.[16] [16] Mr. Frederick Emerson, of Boston, has devised a simple and effective apparatus for removing vitiated air from a room. It is successfully used upon all the public school-houses of Boston. It is now being generally applied to the school-houses and other public buildings, as well as private dwellings, of New England. -=-=-=-=-=-=-=-=-=-=-=-= 512. Why are we insensible to the gradual vitiation of the air of an unventilated room? 513. What is very important in the building of every inhabited room? How can a room be well ventilated? 514. What is said relative to a communication with the external air? -=-=-=-=-=-=-=-=-=-=-=-= 515. In warming rooms, the hot air furnaces, or box and air-tight stoves converted into hot air furnaces, should be used in preference to the ordinary stoves. The air thus introduced into the room is pure as well as warm. In the adaptation of furnaces to dwelling-houses, &c., it is necessary that the air should pass over an ample surface of iron moderately heated; as a red heat abstracts the oxygen from the contiguous air, and thus renders it unfit to be respired.[17] [17] Dr. Wyman's valuable work on "Ventilation," and the work of Henry Barnard, Esq., on "School-house architecture," can be advantageously consulted, as they give the practical methods of ventilating and warming shops, school-rooms, dwelling-houses, public halls, &c.