Page:American Journal of Sociology Volume 9.djvu/844

 8 1 4 THE AMERICAN JO URNAL OF SOCIOLOGY

buckets are used the escape of gases from the sewer is prevented by odor traps (cf. illustration 1 ). For ventilation of the network of sewers, Frankfurt has adapted four old watchtowers. Among the various interesting drawings and models of sewer accessories exhibited by Wiesbaden were several types of -manholes and shafts. One of the exhibiting firms presented an automatic trap for use with single-conduit sewers to prevent sewage from "back- ing up" and flooding cellars in time of excessive rainfall. Dresden exhibited sewer-gates for closing the mouth of the sewer in times of high-water level in the Elbe.

3. Cleaning of sewers. The sewers are generally cleaned by flushing, the main differences being in the apparatus which

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causes the expulsive rush of water which washes the sewer. The best exhibits of such appliances were full-sized objects in opera- tion, shown by the industrial firms which supply the municipalities therewith. The simplest of these appliances, especially adapted to the single-pipe sewer, is a gate either controllable or auto- matic across the lower half, or two-thirds, of the sewer pipe. This holds back the contents of the sewer until a great volume has accumulated. The sudden release, caused by the opening of the gate, permits a rush of the sewage, which carries with it even the heavier materials along the bottom. A second form is a movable dam, for large, walled sewers exhibited by Berlin which is almost the size of the cross-section of the sewer. At the bottom is a comparatively small opening. The sewage, dammed back except at that point, rushes through, carrying with it the sand and similar deposits along the bottom. A third kind of flushing apparatus is a reservoir with automatic siphon discharge, at regular intervals. The chamber of the reservoir is filled by means of a stream of water (from the ordinary water pipes). When the reservoir is full, discharge through the siphon takes "Out