SANITARY SEWERAGE. 533 



cool climate of England a velocity of flow for the sewage of 2' 6 " 

 per second is found to be necessary, in the warmer climate of this 

 country the velocity should be three feet per second. These 

 velocities must be obtained in every instance where sewers are laid 

 down, and under no circumstances whatever should sewage be 

 allowed to stagnate if the greatest efliciency be desired. Failure 

 to obtain these velocities has been a far too common occurrence in 

 the past, and evil results have followed, but no-w, owing to recent 

 advances inhydraulicand pneumatic engineering, the mostdesirable 

 velocity may be obtained under any circumstances whatsoever. 

 Up to the present time sanitary engineers have graded the sewers 

 laid down by them according to the natural features of the site. 

 If the surface slopes happened to be favourable the sewer grades 

 were hIso favourable. Jf the surface happened to be flat, the sewers 

 were laid with infei'ior grades and hence became unsanitary. A 

 rap d flow is also necessary to prevent silt lodging in the sewers ; 

 the velocities before-mentioned ensure this result. 



House sewer connections should dischai'ge their contents (juickly 

 into the sewers. There should be no places in which sewage may 

 find a lodgment and stagnate. All water traps should contain 

 the least amount of liquid necessary for perfect trapping, and 

 should be so constructed that their contents may be renewed at 

 every discliarge into them. All w^ater used for sanitary purposes 

 should be discharged into the house drain immediately after it has 

 taken up the burden of filth for the I'emoval of which it has been 

 applied. 



All refuse water from operations of manufacture should be 

 removed before fermentation has set in. To ensure this quick 

 and eflicient removal all sewer connections should be carefully laid 

 and graded. With the before-mentioned velocity of flow which is 

 about equal to two miles per hour, the sewage may be quickly 

 passed to its destination outside the populated area whilst com 

 paratively fresh. 



The impermeability of sewage conduits is essential. If the 

 sewers be leaky or porous, sewage will pass through into the 

 surrounding ground where it will stagnate and putrify. The 

 resulting gases will penetrate into the sewer and contaminate 

 the air therein. A reverse action will occur in water laden soils. 

 The water will penetrate the sewer, and augmenting the volume 

 of sewage overcharge the system 



It has been shown how very necessary it is to prevent stagna- 

 tion of the sew'age, it is of equal importance to prevent stagnation 

 of the air contained in the sewers. Systematic ventilation of the 

 sewage conduits is imperative. It may be eftectually done. JMany 

 objections have been raised against ventilation of sewers ou 

 account of the oflensive odours which have been found to flow out 

 of some of the ventilators. These objections too often are founded 

 upon facts, and these oflensive odours indicate, badly graded, foul 

 sewers, ill-designed house drains, and putrid sewage. The cure 



