SANITATION 



51 



Internal pressure from the accumulation of a large body of water 

 in any length of piping may be considerable in the case of blockage, 

 and might be sufficient to burst fireclay pipes, especially if these 

 contain faults. Ground subsidence may put a great strain on pipes, 

 but the likelihood of this occurring depends naturally upon the 

 nature of the soil. Drain pipes must have a smooth internal face 

 so that the free passage of waste matter is not hindered. A rough 

 internal surface checks the even flow and facilitates the lodgment 

 of solid particles, which then hold back still more with disastrous 

 results. The internal surface must also resist the corrosion of 

 liquids or gases. Pipes must be durable, be able to withstand alter- 

 nating temperatures, the action of chemicals and the friction of 

 sand and other solid particles. Absolute impermeability to gases 

 and water is an essential feature without which any drain pipe is 

 not only useless but extremely dangerous, as otherwise the surround- 

 ing soil would soon become permeated with sewage and sewer gases, 

 the presence of which is only detected when disease appears and 

 damage is done which might, and should, have been averted. The 

 shape of drain pipes must be such as to offer the least possible 

 friction to the passing fluids, therefore the 

 old-fashioned rectangular-built drains have 

 given place to round pipes. 



If the quality of the pipe is of prime 

 importance, the jointing is no less so; there- 

 fore pipes must be so made that perfect joint- 

 ing can be effected. For this purpose one 

 end of a pipe is fitted with a collar into which 

 fits the spigot end. The joint is made with 

 material which depends on the nature of the Down Pipe. Putty Joint, 

 pipe. The collar or faucet is at the proximal or inflow end and 

 the spigot fits into the collar of the succeeding pipe. 



Drain pipes are made of stone-ware, fireclay or of cast-iron. 

 Stone-ware pipes during the firing process become vitrified through- 

 out the whole thickness of the wall of the pipe and consequently 

 are practically tight ; they are nevertheless salt glazed. On the other 

 hand fireclay pipes are made of a much more refractory material; 

 they are never near the vitrifying point during the firing process 

 and would be fairly porous. To overcome this they are treated 

 inside before firing with a coat of slip glaze which practically forms 

 a thin coat of glass. They are also salt glazed during firing. Fire- 

 clay pipes are mostly used in Scotland as this country possesses 

 no stone-ware deposits. They are made thicker than stone-ware 

 pipes. The thickness of a fireclay pipe is usually one-tenth of its 



FIG. 9. Rain Water 



