FIFTH ANNUAL YEAR BOOK — PART VI. 



535 



people, thoroughly and completely disposes of all organic, eflfete and 

 poisonous matter with no residuum or deposit, and the product flows away in 

 a clear sparkling stream of water, ninety-eight per cent pure by chemical 

 analysis when it strikes the air, the remaining two per cent of impurities 

 being liberated on exposure to the atmosphere, leaving a stream of clear 

 water pure enough for any purpose whatever. That this sewage can enter 

 at one end of a tank a foul, offensive stream, reeking with filth, and emerge 

 from the other end a limpid stream of water, actually pure enough to drink, 

 seems wholly incredible, and yet such is the case, and the wonder of it all 

 is that it cleanses itself automatically, without any artificial agency, solely 

 through the work of the filth bacteria preying upon each other. This 

 system works continually, summer and winter, year in and year out, never 

 freezing. It is practically adapted to use in the country at a distance from 

 city sewers, and even for the use of towns and cities is entirely reliable and 

 effective. 



At the Watertown asylum the system consists of two oblong tanks of 

 70,000 gallons capacity each, placed side by side, one tank emptying into the 

 other through a pipe. For all practical purposes, however, one tank with 

 a weir box at one end, is exactly as good as two tanks, as it has been found 

 that the water as it emerges from the first tank is just as pure as after it has 

 passed through the second tank. The object of this wier box is to check 

 the overflow and prevent any agitation of the sewage in the tank. 



The tanks in this system are located about a quarter of a mile from the 

 buildings. They might be located forty feet or four miles away according 

 to the convenience, the result would be the same. 



The sewage tank as shown in the illustration, consists of a brick box 

 with eight-inch walls and floor, lined within and without with cement. Con- 

 crete would make a better tank. The roof is made air tight with a heavy 

 coating of pitch and all crevices are tightly sealed with the same material. 

 The sewer inlet is about two feet below the surface of the sewage in the 

 tank. A short distance from the opposite end of the tank a cross wall is 

 built, having a narrow opening extending across the tank on a level with 

 the inlet. This opening has little if any greater capacity than the inlet. 

 Such an opening causes less current in discharging than would a circular 

 opening. In the end wall is a row of curved tile so placed that the out- 

 lets are two feet above the sewer inlet and the opening cross wall. The 

 cross wall forms a weir, or dam, which retards the outflow from the main 

 tank, and of course there can be no discharge until the contents of the 

 tank and weir box reach the level of the curved tile outlets. Thus both 



