Hygiene and public health / by B. Arthur Whitelegge.

  • Arthur Whitelegge
Date:
1894
Catalogue details

Licence: Public Domain Mark

Credit: Hygiene and public health / by B. Arthur Whitelegge. Source: Wellcome Collection.

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    or vacuum in the room to be ventilated. Fresh air may be driven into a room or building by revolving fans or other motors ; vitiated air may be extracted by means of fans, steam jets, or a heated outlet shaft. The fans used for the purpose have vanes set obliquely upon a rapidly revolving axis, and work in a closed box or tube so as to propel a constant current of air of any required volume and velocity, somewhat after the manner of an Archimedean screw. Steam allowed to escape in a powerful jet into a flue is capable of carrying with it 200 times its own volume of air. Gas may, by means of extraction shafts, be made to carry off a thousand times its own volume of air. Heat is by far the most generally employed motive power. Ordinary fire-places, chimneys, and venti- lating gas-lights act in this way. Special extraction shafts, with gas jets or furnaces at the bottom, are common. Mines are ventilated by means of a furnace at the foot of the upcast shaft, air being drawn down another shaft and made to traverse the whole of the workings on its way to the upcast. A similar plan is adopted in steamers, the upcast being a space around the funnel and boilers, a contrivance which has been applied also to house chimneys by confining the smoke, etc., to an iron tube passing up in the centre of the chimney shaft. Extraction is, upon the whole, the more convenient and satisfactory method, but is attended with some disadvantage from the difficulty of controlling the sources from which the supplies of fresh air are drawn, since it rushes in through all available openings. Provision may, how- ever, be made at suitable points for admission of pure air, which may be warmed, cooled, moistened, washed, or screened, as it enters. When propulsion is adopted, the air is taken from one source only, and, being more under control, is more readily subjected to such heat- ing or other treatment as may be needed.