RAILWAY CONSTRUCTION. 225 



turned over at the ends to grip the outside flanges. Being made 

 to exact template, they have to be threaded on to the rails 

 before spiking down, and are placed between the sleepers at 

 distances from 7 to 10 feet apart. 



Laying Permanent Way. To preserve a good line and level 

 to the permanent way, it is absolutely necessary that the road- 

 bed should be kept thoroughly drained. If provision be not 

 made for quickly carrying away the rain-water, and if it be 

 allowed to collect under and around the sleepers, the action of 

 the passing trains will work the finer particles of the packing 

 into the consistency of soft mud, which will be gradually squeezed 

 away, leaving the sleepers imperfectly supported and insecure. 

 A loose sleeper involves a depression in the rails, and a corre- 

 sponding lurch in the vehicles of the train, and a series of these 

 depressions may produce such an oscillation in the train as to 

 cause it to leave the rails. 



The height or space from formation-level to rail-level is 

 generally about 1 foot 9 inches for a flange railroad, and about 

 2 feet for a chair railroad. 



Figs. 336 and 337 show cross-sections of both descriptions of 

 road as laid down for a double line in cutting. The same 

 arrangement applies to similar roads laid down in embankment, 

 merely omitting the side-drains or water-tables. The bottom 

 layer of ballast or road-bed should consist of good hard, quarried, 

 or broken stones, each 6 inches deep, set on edge, firmly and 

 closely hand-packed, forming a foundation through which the 

 rain-water can be quickly carried away. On the top of this 

 bottom pitching should be placed a 6-inch layer of broken stone 

 ballast or strong clean gravel, of which none of the stones should 

 be larger than will pass through a 2-inch ring. When the 

 sleepers and rails have been laid on this second layer, and 

 properly packed to line and level, the top ballasting, or boxing, 

 of either broken stones or strong clean gravel, should be filled 

 in to the form and extent specified. Where broken stones are 

 used for the top ballasting none of them should be larger than 

 will pass through a 1^-inch ring. 



Broken stone ballast should only be made from the hardest 

 and soundest description of rock or boulders, so that, however 

 small the particles, they will remain sharp and clean. 



There are many kinds of rock which appear hard and 

 compact when first excavated, but upon exposure to the weather 



Q 



