Aids to sanitary science : for the use of candidates for public health qualifications / by Francis J. Allan.

  • Allan, Francis J.
Date:
1903
Catalogue details

Licence: In copyright

Credit: Aids to sanitary science : for the use of candidates for public health qualifications / by Francis J. Allan. Source: Wellcome Collection.

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    (a) Surface supply, from rain, snow, brooks, rivers, lakes, surface-fed springs and shallow wells, etc. {b) Supply from deep subterranean sources, as from springs cropping out at the foot of mountain ranges, from natural reservoirs, from artesian and other deep wells. Rain-water in this country, on account of atmospheric impurities, is seldom stored except for external use. The uncertainty of rainfall also tells against its use. One gallon of rain contains on an average eight cubic inches of gases, the oxygen being in larger proportion (32 per cent.) than in atmospheric air ; the carbonic acid amounts to only about 2 per cent, of the mixed gases. In the neighbourhood of human dwellings the rain con- tains soot, sulphuric acid, tarry and other matters derived from the combustion of coal, and ammoniacal salts, nitrates, albuminous and other organic matters derived from decomposing animal and vegetable substances, and the exhalations from the bodies of men and animals, together with various debris and innumerable micro- organisms, bacteria, micrococci, moulds, pollen, etc. When properly collected, however, rain-water can be stored and utilized for all domestic purposes. When it is decided to collect rain-water from the roofs of houses, a ‘rain-water separator’ should be employed. This con- sists essentially of a self-acting canter, balanced upon a pivot, which cants and directs into a waste-pipe the first lot of water, which has washed the dirt from the roof. Since it never contains more than a trace of lime-salts in solution, it is exceedingly soft, and well adapted for wash- ing. By proper filtration it can be rendered'potable. Rain-water, especially in certain districts where manu- facturing towns abound, frequently contains a distinct trace of sulphuric acid, and then acts freely on various metals. It is not safe, therefore, to store it in lead, zinc, iron, or galvanized iron tanks. For small cisterns earthen- ware may be used. If slate tanks are used, the joints being made with white or red lead, the angles where the lead is exposed should be filled with cement. Brick storage tanks should be well puddled outside with clay, and lined inside with Portland cement. Ice-water is heavy and non-aerated. Water in freezing loses part of its saline contents, but it should be re-
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