DRAINAGE. 43 



need not exceed i in loo, giving a velocity of 3 feet per 

 second; they should be without right-angled junctions or 

 sharp bends, and the gradients may be regulated in long 

 distances by a judicious use of cesspits. 



These pipes are often jointed in clay, which can only be Jointing pipes 

 considered superior to cement in exceptional cases ; where, ^^ ^ ^^* 

 for instance, the ground is liable to subsequent settlement, 

 that would cause a fracture to a too rigid line of pipes. The 

 joints should have two layers of tarred yarn forced into the 

 bottom socket, and the entire remaining space between the 

 spigot and socket filled up with tempered clay, well driven 

 home with proper tools. The joint, externally, should also 

 be enveloped in a band of clay. 



In most cases, however, the use of Portland cement is to be Cement joints, 

 recommended, in preference to clay, and it is sometimes 

 necessary to take the precaution of bedding the pipes half 

 way up in a concrete cradle. The caulking should be done 

 all round with oakum or gaskin, which will prevent the cement 

 escaping through the joints. Wooden scrapers should also 

 be used as the work proceeds, to remove any portions of 

 cement that may afterwards harden and stop the passage. 

 All liquid should be carefully excluded from the pipes until the 

 cement is set, nor should they be covered in until it has 

 completely hardened. It is a good plan to let the socket of 

 every pipe rest on a bedded brick that the joints may be 

 more effectually caulked. The cement used should consist of 

 one part of cement and two parts of clean sharp sand. 



In all cases where the ground has "to be filled in, a liberal Filling in. 

 use of water by means of a hose should be allowed to run into 

 it, so that as firm a bed as possible may be obtained for the 

 concrete and paving. 



Four-inch drain pipes, as shown on Plates 32 and 50, will Velocity in 

 suffice as branches from the stables and gullies, but they should P^P^^* 

 be of 6-inch diameter from the men's closets, and have a 

 fall of not less than i in 150, which will give the same velocity 



