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.

    70/610 (page 58)
    chalk, and 20 per cent, on limestone, while upon clay scarcely any infiltration occurs. For obvious reasons the proportion is less in hilly districts, which otfer greater facilities for surface-flow, and less in summer than in winter owing to excessive evaporation. Experi- ments upon a gravelly loam indicated a jDenetration of only 2 per cent, in summer and nearly 100 per cent, in winter. Raiti-water is soft and well aerated, but its purity and fitness for drinking or even for washing depend upon the purity of the atmosphere through which it falls. Near the coast it often contains traces of chlorides and sulphates, due to its sea-origin. It acquires from the air not only oxygen, nitrogen, carbonic acid and ammonia, with a minute amount of nitric acid, but also microbes and any organic or other impurities that may be present in the air. In inland districts there is a marked increase in the sulphuric acid, aniDionia, and organic matter, due to putrefactive processes and the combustion of coal. Near towns rain may become acid in reaction, from excess of sulphurous and sulphuric acids, and is liable to carry down considerable quantities of tarry and carbonaceous matter from the smoky air. Ammonia is found in largest proportion during the early part of a shower. A litre of rain contains about 25 c.c. of gases, namely, 8 c.c. of oxygen, 16*5 c.c. of nitro- gen, and 0-5 c.c. of carbonic acid. Dew and snow- water have practically the same characters as rain- water, except that the dissolved gases are in less amount in snow^-water. Spring's and wells.—The portion of the rain- fall that sinks into the ground becomes heavily charged with carbonic acid from the air in the inter- st^^ces of the ^jjl aided by this and by the increas- ing pressure itdissolves out lime and various mineral salts from the strata through which it passes. From