SANITATION 



59 



probability that it will not be completely removed with a moderate 

 Hushing. It is advisable for the inlet to provide a sudden fall 

 so as to give some impetus to the outgo of sewage, but the outlet 

 should be more gradual so as to render easy the discharge of solid-. 



One of the earliest forms of traps is the dip-stone, masons or 

 built trap. This, as the figure shows, is a receptacle built of brick 

 or other mason's material for containing a body of drainage into 

 which dips a flagstone which is supported by being built into two 

 sides of the structure. The dip-stone is supposed to prevent the 

 backward passage of gases into the inlet pipe. It is one of the worst 

 forms of traps and is figured for the purpose of showing its bad 

 points. Owing to the nature of its formation there is liable to be 

 a settlement of part of the structure with resultant leakage at the 

 top of the dip-stone, and the whole fabric may allow sewage to 

 escape into the surrounding ground. The trap is not self -cleansing, 

 and indeed it is impossible to clean it out thoroughly by any method. 

 The dip-stone becomes coated with organic scum, which remains 

 to decompose and give off noxious gases which pass up the inlet pipe. 

 Solids settle to the bottom of the chamber, accumulate, and grad- 

 ually putrefy on both sides of the seal. It is indeed a " trap," 

 but not in the sense that is intended to be implied. 



Figure 20 illustrates the trap in use to-day. It was designed 

 by Buchan and is called Buchan's Disconnecting Syphon Trap. 

 The illustration shows 

 that it is provided with an 

 abrupt inlet and a gradual 

 outlet. It might be 

 thought that the water on 

 entering this trap would 

 strike the perpendicular 

 wall facing the inlet and 

 thus check the flow ; this, 

 however, is not so because, 

 should the water enter 

 with sufficient force to 

 carry to the opposite side of the inlet, then the pipe would be 

 running full bore and there would be no question of the trap not 

 being completely flushed. Should the pipe be running less than at 

 its full capacity, the sewage would fall over into the centre of the 

 trap, thus forming Buchan's Cascade, the object of which is to 

 break up any scum that may have formed on the surface of the 

 water seal. The seal in this trap is very effectual, and the body of 

 water retained is just sufficient and no more to fulfil its intended 



FOR CLEANING 



OR VtNTILATIXG 



FIG. 20. Buchan's Disconnecting Syphon 

 Trap. Note the abrupt inlet giving a 

 cascade action to the inflowing fluid. 



