628 THE AMERICAN JOURNAL OF SOCIOLOGY
serves both as source and as reservoir. Spring water and filtered ground water are used in Frankfurt a. M. for drinking purposes; but for street-sprinkling and manufacturing purposes, etc., water is pumped from the river Main and distributed through a sepa- rate system of water pipes. Wiirzburg uses spring water, but has separate water works for furnishing ground water, from near the river bank, for the Ring parks. Twenty-one cities of the thirty- five with exhibits in this section use ground water. The source is always near a river ; but the water is said to be pure, needing no filtration save when it contains too high a percentage of iron. Augsburg and Darmstadt sink well-shafts into underground streams, and pump the water thus collected to the water-works. Leipzig has to remove the excess of iron. Kiel exhibited a model of the works for removing the iron. The water is caused to trickle over an apparatus through which streams of air are forced. The iron is oxidized and precipitated, and then readily filtered out. Berlin uses filtered river water, mostly. The water is cleared in settling basins, then pumped into the sand filters, from which it is led to the reservoirs. An excellent model on a scale of 1 : 50 showed the water-works at the Miigglesee, from which Berlin draws a part of her water. Engines pump the water into a collector, whence it passes to the Enteisenungsanlage (" iron- removing apparatus"). The water is next pumped to the sand filters, where it seeps through a thick layer of fine sand, then through a layer of coarser sand, next through a layer of fine gravel, then through a layer of coarse gravel, and finally through a layer of pebbles, in which are the innumerable opening of pipes through which the water is pumped to the reservoirs. The reser- voirs are roofed over with arches of masonry, and covered with turf ; so that the heat of the sun does not penetrate in summer, and freezing in winter is avoided. Bremen takes the water of the river Weser, collects it in settling basins, and then pumps it into sand filters, from which it is pumped into the reservoirs. A model exhibited by this city showed how the water may, when occasion demands, be pumped from one filter into another, and so be twice filtered, Breslau likewise derives her water supply from her river, the Oder, and filters it by means of sand filters.
