Food : a brief account of its sources, constituents and uses / A. H. Church.

  • Church, A. H. (Arthur Herbert), 1834-1915.
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: Food : a brief account of its sources, constituents and uses / A. H. Church. Source: Wellcome Collection.

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    nitrogen, oxygen, and carbonic acid gas; and if there be any sulphurous acid gas, or hydrochloric acid, or compounds of aisenic, etc., present in the air—as in and near large towns and manufac- turing districts, it will carry these down with it. But it will also remove from the air much of the suspended matter which is always floating therein—the dust which is seen to be so abundant in air when a beam of sunlight falls across an otherwise darkened room. Thus it is that rain-water, or ever it touches a roof of the land, contains of solid impurities, organic and inorganic, nearly 2 grains in the gallon. This is the average result in the country, but the rain-water of London and large towns is far more loaded with impurities. Here it will be as well to state that the amount of rain falling in the London district averages less than 25 inches in the year : it is less than this on the eastern coasts of England, and gradually increases towards the west till there are found some excessively rainy places, as in North Wales, Cumberland, and the north-west of Scotland, where the annual rainfall is greater than 75 inches. Let us consider what one inch of rain really means. If an acre of land were covered with water to the depth of only the tenth part of an inch, that layer of water would weigh more than 10 tons : thus 1 inch of rain is ten times that amount—in fact, very nearly 101 tons. A rainfall during the year of 25 inches corresponds, then, to 2,525 tons of water per acre. If we collect rain-water as it falls in the country, we may easily render it impure in many ways. If it falls on a slate roof it suffers little change; if on one of tiles, it will take up scarcely anything save a little decaying vegetable matter from the mosses and lichens usually found on such a surface; but if it falls on a limestone roof it dissolves calcareous as well as decaying organic matters. Further, rain-water acts on leaden pipes and cisterns, becoming charged with this injurious metal. 2. River-water.—Directly rain-water comes into contact with the land it acquires fresh impurities. Even rain-water stored