44 STABLE BUILDING AND STABLE FITTING. 



as a 4-inch drain with a fall of i in loo, viz. 3 feet per second, 

 both pipes running half-full under the same conditions. A 

 9-inch pipe would have a fall of i in 225, a 12 -inch pipe a fall 

 of I in 300, and an 18-inch pipe a fall of i in 450. The size 

 of the main drain is regulated by the number of horses, but 

 is rarely required to be above 9 inches. 

 Manholes. Manholes, inspection, and ventilating pits are, with few 



exceptions, necessary only in long lengths of drains ; but the 

 first of these is often required at important junctions. The 

 author was, on one occasion, obliged by the authorities to con- 

 struct a small manhole on premises where he was carrying out 

 some stable buildings simultaneously with a drainage scheme 

 for the town, as illustrated by the manhole h on Plate 39. 

 Plans and Sections of one of these manholes, with the angle 

 footiron used, are illustrated on Plate 49. It is of exceedingly 

 simple and inexpensive construction, and was built for an egg- 

 shaped sewer, 2 feet by 3 feet. 

 Inspection Pits for the purpose of inspection and cleansing are built 



^^^^' with the pipes running through them, having a 2 -foot length of 



pipe with a movable section, as shown on Fig. 20 ; by the 



Fig. 20. 



insertion of a chisel at the ends, the upper piece may be 

 detached, and replaced. The pits are closed in with air-tight 

 covers. A drain should be ventilated at every 300 feet. A 

 cement-jointed vertical drainpipe built into a chamber of brick 

 in cement is one of the simplest methods. The outlet should 

 have a strong cast-iron grating (bedded on cement brickwork), 

 as shown in Fig 21. The inside surface of the brickwork, at 

 both ends of the pipe being rendered J -inch thick with Portland 

 cement. 



