h = distance between top of chimney and floor of room in question, and thus the velocity with which air enters is governed by the difference between the internal and external temperature, and the height from which the cold air descends in order to take the place of the air which has escaped.
[CHAPTER XXII.]
METHODS OF VENTILATION.
In most houses no special means of ventilation are provided, windows, doors and fire-places being trusted for ensuring a sufficient supply of fresh air. These do not suffice in well-built houses, unless the inhabitants train themselves into enduring the currents of air necessarily associated with open windows and doors. They are, however, aided in the majority of houses by the porosity of walls, by currents of air through crevices of wood-work, and so on. It is desirable that adequate special provision for ventilation should be made for every house when it is built, and that as much care and forethought should be exercised in this respect as in the laying on of a water-supply or sanitary appliances connected with drainage.
Whatever the system of ventilation adopted, it is wise to flush rooms frequently with fresh air. This is best effected by throwing the windows wide open whenever a room is left unoccupied. In this way a much more thorough and complete purification is effected than by any other means. This is especially important in the case of bedrooms, in which organic impurities are most prone to accumulate.
Not only should rooms be ventilated, but likewise the furniture they contain. This again is most important for bedrooms. Beds should not be “made” till sometime after using; and in the interval, should be freely exposed to the air. The same applies to night apparel.
It is well to allow rooms to lie fallow at intervals. Organic matter accumulates about a room, and devitalises any air which enters. If the room is vacated, and flushed with air for a continuous period, it becomes sweeter and purer. The importance of this is now well recognised in the case of hospital wards. Such temporary disuse of rooms must not, however, be regarded as sufficient without thorough cleansing of every surface in them, in order effectively to remove all organic and other dust.
An Inlet and Outlet for air should both be provided. According to some an inlet only is required, while others would only provide an outlet; but a perfect system of ventilation requires both. As heated air expands, the outlets should theoretically be larger than the inlets; but as the average difference of temperature is only 10°-15° Fahr., the expansion is only slight, and may be practically neglected.
The necessity for both inlets and outlets may be illustrated by a single apparatus like that shown in Fig. 11. A taper is burning at the bottom of the jar, in the stopper of which two tubes, A and B, are placed. So long as both tubes are kept open the candle will keep alight, but if A be blocked, the candle goes out.
