The air is let into the rooms at about 65° F., and the authors remark that, when there are living beings in the room, their bodies are at 98o F., and the vitiated air ascends and the incoming warm air descends. Though carbonic acid gas is heavier than air at the same temperature, they consider that there is no danger of its settling near the floor, because of its small proportion, and the speedy diffusion which takes place between gases.

Fig. 499.   Section through Floor of Corridor showing Passage of Heated Air.

Fig. 499. - Section through Floor of Corridor showing Passage of Heated Air.

Fig. 500.   Section showing Air inlet from Corridor to Room.

Fig. 500. - Section showing Air inlet from Corridor to Room.

Fig. 501.   Section showing Air outlet from Room.

Fig. 501. - Section showing Air-outlet from Room.

The Hues must of course be as smooth as possible inside, in order to afford the least obstruction to the passage of the air. Each room must be provided with a separate outlet-flue, and this must lead direct into a foul-air chamber at the top of the house; all the foul-air flues must come into this chamber at the same level. The foul-air chamber itself was in this case constructed of zinc, and was perfectly air-tight; from the base of this chamber descends the main foul-air flue, and this should go direct to the base of the kitchen-flues. All the passages should be so designed that the velocity of the air travelling along them should not exceed 150 to 200 feet per minute. The authors discuss various methods of creating the necessary suction to get rid of the foul air, but conclude that the kitchen-chimney is the best. The upcast foul-air flue must be separated from the back of the kitchen-fire by a sufficient thickness of fire-brick, and the smoke-flue should preferably be of iron, so that as much heat as possible should be given off to the foul-air flue. They propose that the kitchen smoke-flue should be fixed in the centre of the square foul-air upcast shaft, and that the top of the opening of the smoke-flue should be restricted to 9 inches diameter, which they consider ample, after carefully experimenting upon the-subject. If, after trial, the heat evolved by the kitchen-fire is found inadequate, then a few coils of Perkins's hot-water pipes, or some jets of gas. might be added. They have, however, found that in houses of moderate size, the kitchen fire suffices. The cross areas of the upcast shafts taken together should exceed the cross area of the downcast shaft, and there should be a special valve for regulating the size of the outlet for each room separately. From experiment upon the two houses already alluded to, the authors found that the velocity of air in the upcast shaft was about 400 feet per minute.

In cases where the houses are already built, it may be impossible to use the kitchen-flue as an upcast shaft; it would then be advisable to use gas-jets close to the outlets of each of the rooms, and probably a ring of gas-jets at the top in the foul-air chamber. While the problem of warming and ventilation may have been satisfactorily dealt with by the authors for special cases, it must always be remembered that the two houses referred to were specially designed for the system described, and such a system is not easily applicable to houses already built, with the front and back doors both possibly opening into the main hall or corridor, and both in direct communication with the central staircase.

In the country, the air is usually sufficiently clean to be admitted without filtration, but in towns it is so loaded with soot and dust, that some method of cleansing it is eminently desirable. As soon, however, as filtration is resorted to, cooeiderable resistance will have to be overcome, and I consider that in many cases it will be necessary to resort to the use of a ventilating fan, if certainty of action is to be secured, but such a fan is quite out of the question in a house of small or moderate size, unless an electric motor be used. The employment of electricity for the purpose would simplify the problem considerably, and would render unnecessary the use of the downcast and upcast Hues. It is not desirable, however, to be dependent upon the action of such a fan for the warming and ventilation of an entire house.