24 ON THE D1SP08AL, OF SEWAGK. 



The automatic flushing-tanks are a noticeable feature in ihe 

 system. Placed at the head of each lateral sewer they can be 

 discharged as often as may be deemed advisable to keep the line 

 of pipes free from gas or any obstruction — the frequency of their 

 discharge being regulated by the quantity of water flowing into 

 them in a given time. The effect of each discharge would be 

 the sudden entrance into, and passage along the sewer of 120 or 

 loO gallons of water, according to the size of the tank, which 

 would force the air contained in the sewer out through the house 

 connections, and forming a vacuum as it proceeded, fresh air 

 would readily enter from the house drains. The house connec- 

 tions are continued above the roofs of the houses ; no nuisance, 

 therefore, would be caused by the escape of the air forced 

 thi'ough them from the sewers at each discharge of the flushing- 

 tank. The cost of the system in America is about one dollar 

 per foot. At Keene (jl,232 feet of sewers cost .'?7(J,UHS-8o, 

 including construction, superintendence, land damage, tees. Sic. 



Tlie disadvantages of a separate system are, that separate 

 channels and pipes have to be provided for the rain ; tJ)at the 

 rain from all larger cities carries from roofs and street much 

 organic deln-is, which pollutes the river or watercourse into 

 which it may be discharged. But with the combined or single 

 system the drains re<iuire to be much larger, and storm overflows 

 must be provided, sufficient to carry oft" the storm water whecp 

 the drams get filled, and with this storm water the whole 

 contents of the sewers are discharged, so the stream would run 

 greater risk of being polluted in this way than if the surface 

 water only were allowed to flow into it. However, the second 

 objection to the Separate System lias been done away with by 

 an ingenious contrivance of Mr. Horace Andrews, by means of 

 which the first portions of rain water, containing the foulest 

 parts of the street washings, etc., may be intercepted, and be 

 thus prevented from polluting any watercoiu^e into which they 

 would otherwise run. It consists in placing an intercepting 

 <hain at a lower level than the conduits for rain water, and so 

 arraaaged that the contents of the conduits Will flow into it until 

 they increase in volume and rapidity sufficiently to shoot over 

 the drain, by which lime they are comparatively pure. 



