The Elements of Hygiene for Schools (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 Excerpt: ...be discolored from mineral or vegetable causes and frequently has an odor as well as an unpleasant taste. The purity of water can only be determined in the laboratory. The amount of water per capita daily supplied in a large number of cities in the United States varies from 300 gallons in Denver to 48 gallons in New Orleans, the average being about 150 gallons; this includes water for all domestic and commercial purposes. The purification of water is accomplished by physical, chemical, and mechanical means. Formerly mechanical means only were employed, a water that was clear being considered fit for drinking purposes, but with the knowledge acquired by recent investigations it is now known to be of much more importance to free the water of all pathogenic bacteria as well as of some harmful mineral substances. Self-purification of water.--That the water of running streams and lakes is largely self-purifying has long been recognized. This self-purification occurs by sedimentation or the settling of solid matter and by oxidation, whereby in its movement the water comes in contact with oxygen, which oxidizes the organic matter; sunlight also destroys some bacteria. The entrance of pure water from tributary streams dilutes polluted water, rendering it less harmful; many water plants purify water of undissolved organic substances, and pathogenic bacteria may be destroyed by the saprophytic class. An interesting sample is cited by Jordan1 of observations made along the Chicago drainage canal and its connecting rivers, the Des Plaines, Illinois, and Mississippi. "In the flow of twenty-four miles between Morris and Ottawa, the river freed itself from a great mass of sewage bacteria with which it was originally laden, and at Ottawa this was not greatly in excess...