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.

    15/610
    CHAPTER I. AIR. Pure air contains about 21 per cent, (by volume) of oxygen, and about 79 per cent, of nitrogen, but there are also traces of ammonia and carbonic acid, and a very variable amount of watery vapour. The sus- pended solid matter includes organic and mineral particles, and microbes. Oxyg^eii.—^The purest sea or mountain air con- tains 20-999 volumes per cent, of oxygen, and the vi^orst air found in a mine 18'27 per cent. (Angus Smith). In over-crowded halls the percentage may be as low as 20'65. Even in the open air of towns it varies widely, considering the narrow limits stated above, but 20*96 per cent, may be taken as an average. It is lessened by respiration, by combustion, by putre- factive processes, by organic effluvia, and by fog ; but increased by vegetation and by rain. Ozone is an irrespirable gas, regarded as a more active allotropic form of oxygen, with the molecular formula instead of O^. It appears to be only an occasional component of air, and never present in more than minute traces. Although these do not admit of exact measurement, the proportion is greatest after thunderstorms, and greater on the coast than inland. The ozone reaction (page 17) is more often met with when the wind is S. W. than when it is N.E. Ozone is readily reduced by oxidisable matter, and its presence, therefore iinjilifigL-ai^sence of organicjmpurity in tiie air. Carbonic acid is usually adopted as the measure of the impurity of air, to which it bears a fairly constant relation. It varies from 0*3 per thousand in the purest mountain or sea air to 1 0, 2*0, -X-