158 president's address — section h. 



h. The separate system, in which surface and subsoil 

 waters are completely excluded, and are each pro- 

 vided for by separate drains. 



c. The partially separate system, in which a certain 



quantity of storm-water is admitted into the sewers, 

 generally that falling on the back roofs and yards 

 of houses. The surface and subsoil waters are 

 each disposed of by separate drains as in the 

 separate system, 



d. A system proposed by Captain Liernur, in which the 



surface and subsoil waters are dealt with separately, 

 the liquid wastes separately, and the solid excreta 

 separately ; the sohd excreta is removed by cast- 

 iron pipes, in which a vacuum is created by means 

 of engines and air-pumps at a central station, 

 where furnaces are provided for converting the 

 material conveyed by the cast-iron pipes into a 

 poudrette manure. 



e. Shone's system, which consists in dividing up a town 



into a number of districts, each with its separate 

 ontfall and discharging station, the discharge from 

 all the stations converging into one common main 

 leading: to the ultimate common outfall. This 

 system is applicable w^hen the rain-water is entirely 

 excluded, or when it is admitted to a limited extent. 

 1 will first deal with the three separate and combined 

 systems. 



From a mechanical point of view, the combined system 

 performs all the offices required of it in a more or less satis- 

 factory manner, but the disadvantages are obvious. The 

 admission of subsoil water necessitates porous joints, and in 

 times of drought the sewage will flow outwards and con- 

 taminate the ground. The large size of the sewers necessary 

 to convey storm-water i-enders them most insanitary during 

 the dry weather flow, oAving to the large surface exposed to 

 decomposition. Again, the surfiace waters carry with them 

 during heavy rains much sand and silt, which remains to 

 some extent afterwards, forming a nucleus for the deposit of 

 the solid portions of the sewage and subsequent decomposition, 

 resulting in the generation of foul gases, which may increase 

 in pressure sufficiently to force the traps of the house drains. 

 The street gully catch-pits become most oflensive, as they 

 are local centres of decomposition, intercepting as they do 

 the horse manure, mud, and street sweepings, whereas these 



