SANITARY SCIENCE. 



725 



complaint and made necessary an enlargement 

 of the sewer system. 



Sewer-Ventilation. It is the duty of the public 

 authorities to ventilate the sewers, without 

 depending upon house connections. In Frank- 

 fort, Berlin, Hamburg, and Dantzic, soil-pipes 

 act as sewer-ventilators; but there the house- 

 drains are properly designed and securely laid, 

 under official supervision. Where perforated 

 man-holes fail to dilute and render harmless 

 the sewer-air, the fault may be traced to the 

 inadequate number of these vents, or the need- 

 lessly foul state of the sewer due to deficient 

 inclination, excessive size, improper form, rough 

 materials, irregular gradients, badly devised 

 junctions of branch inlets, favoring deposit, 

 etc. With care on the part of the authorities, 

 all these deficiencies may be corrected. 



Many methods have been suggested for venti- 

 lating sewers, but no thoroughly satisfactory 

 plan has been adopted, except to supply per- 

 forated man-holes at frequent intervals along 

 each sewer, and to allow the latter to ventilate 

 by diffusion. Every little while some wiseacre 

 writes to the newspapers proposing an entirely 

 new and original method of ventilating sewers 

 by connecting them with fires in furnaces, fac- 

 tories, or other large buildings, so as to destroy 

 the noxious qualities of the sewer-air. It has 

 also been proposed to have large lamps for 

 lighting the streets, which could be connected 

 with shafts from the sewers, and thus the foul 

 gases would all be consumed. Another ingen- 

 ious individual has proposed to destroy these 

 gases by electricity. The radical difficulty 

 with all such methods is the disproportion be- 

 tween the means proposed and the vast area of 

 the sewers, which cover miles of space. Such 

 an appliance to draw out the foul gases from 

 the sewers would need to be multiplied on a 

 vast scale in order to produce any effect, as the 

 draught upon one part of the sewers would 

 tend to be neutralized by the down current 

 through man-holes, catch-basins, and other 

 openings into the outer air. No general plan 

 for sewer-ventilation has yet been found. Some 

 expedients succeed in one place, and some in 

 another. Charcoal trays in man- holes check 

 ventilation. Draughts by special chimneys 

 exert an influence over a very limited district. 

 To prove efficient, a chimney must be placed 

 at every street corner, and a special fire main- 

 tained at great cost. Gas-burners are a still 

 more costly device for creating a draught. If 

 sewers and cess-pools are ventilated, the vol- 

 ume of foul gas will be small within them ; 

 while if the sewage is carried off at once to the 

 outlet, there will be less chance of decompo- 

 sition and a less volume of gas exhaled. To 

 accomplish this end, sewers must be well con- 

 structed, with smooth interior surfaces and true 

 gradients with facilities for preventing or re- 

 moving deposits and for free ventilation, so 

 that any gases will be dissipated rapidly into 

 the outer air. By diluting sewer-air it may be 

 rendered practically harmless. 



Pressnre of Sewer-Gas. There has been consid- 

 erable discussion as to whether pressure is ex- 

 erted by the gases from sewers. Prof. Chan- 

 dler failed to discover any evidence of such press- 

 ure in siphon-gauges that were placed upon 

 plumbing fixtures in houses and at the School 

 of Mines. But it is a common experience with 

 plumbers to find very strong pressure in pipes 

 connecting with sewers. If the temperature 

 of the outer atmosphere is lower than that of 

 the sewer, as in winter, there will be a strong 

 inward current of air ; but when the conditions 

 of temperature are reversed, the outward press- 

 ure will often be great enough to extinguish a 

 candle. Temporary wooden plugs at the ends 

 of soil-pipes have been blown out with great 

 force during heavy rain-storms. When sewers 

 become gorged by storms especially in locali- 

 ties like Brooklyn, where there is an enormous 

 drainage area to be provided for the foul air 

 is forced out in every direction. James C. 

 Baylis mentions seeing a miniature waterfall 

 over a perforated man-hole in a Brooklyn 

 street where the sewer was too small, and 

 where the belching gases blew the water up 

 in a continual spray. In Washington a sewer- 

 arch was broken by the pressure of rain-water, 

 causing great damage. In many localities it is 

 necessary to supply security against back press- 

 ure from sewers that are tide-locked, or become 

 gorged with rain by placing valves upon house 

 connections. Several forms of valve can be 

 used for this purpose. They can be inserted 

 just as a section of pipe can be put in. The 

 best way is to insert such a valve in the line to a 

 drain as near the sewer as it can be accessible 

 for opening and repair. The old form of valve 

 intended to be placed at the end of a drain is 

 inadmissible. 



The effect of steam in sewers is becoming an 

 important consideration. Many business estab- 

 lishments that employ steam-power discharge 

 their waste steam into the sewers, though this 

 is forbidden by law. Decomposition is thereby 

 hastened, and the sides and top of the sewer 

 become coated with an offensive slime, which 

 can not be washed off excepting during heavy 

 rainfalls. If the sewer is of brick, the mortar 

 is decomposed and an exit made for foul gases 

 under such pressure that they force their way 

 into basements and cellars. The lead joints of 

 house-plumbing connections are often blown 

 out by the steam pressure, which will also force 

 traps or dry out their contents. In a large dry- 

 goods establishment in Broadway, where waste 

 steam discharged into the soil-pipe, the pressure 

 forced several joints, so that part of the build- 

 ing was flooded and damaged to the extent of 

 several thousand dollars. Explosions of illumi- 

 nating gas from leaky mains frequently occur 

 in sewers, the gas saturating the adjacent soil 

 and readily finding its way into the sewer. Sev- 

 eral such explosions occurred during the con- 

 struction of steam-heating mains in New York. 

 In that city the waste of illuminating gas from 

 leaks is from 6 to 10 per cent. A peculiar gassy 



