RAILWAY CONSTRUCTION. 209 



Chairs have been made, as in Fig. 299, with a recess in the 

 rail-seat, to hold a piece of prepared wood, or other suitable 

 semi-elastic material, the object being to provide a rest, or 

 cushion, softer and more yielding than the cast-iron. The idea 

 looks well in theory, but in practice the pounding on the rail 

 compresses or crushes the wood lower and lower into the recess, 

 slackened keys have to be tightened, and when the wood has 

 been worn or crushed away down to the level of the stop ribs, 

 A, A, the under side of rail has no longer any seat, or rest, beyond 

 the two narrow ribs of cast-iron. These afford such a very 

 limited support that the rail becomes notched, and produces a 

 very rough clattering road. It is a very simple matter to take 

 out an old key and put in a new one, but to replace a wooden 

 cushion in a chair recess involves the entire removal of either 

 the rail or the chair. Chairs with wooden cushions have not 

 been adopted to any great extent, the tendency of modern 

 practice being to reduce as far as possible the number of parts of 

 the permanent way, and to provide those parts with ample 

 bearing or contact surfaces. 



Although the general practice has been to cast the chairs in 

 one piece, chairs have been made in two pieces, as in Fig. 300, 

 fastened together and to the rail by a bolt passing through the 

 latter, the castings being secured to the sleeper with spikes. At 

 first sight this pattern of chair appeared to possess some features 

 in its favour. The castings were simple, keys were dispensed 

 with altogether, and the under side of rail was not in contact 

 with the cast-iron. A short experience, however, proved that 

 the drawbacks far outweighed the apparent advantages. Holes 

 for the through-bolts had to be punched at fixed distances in the 

 rails, and although this could be readily done at the works, for 

 the general use on the line it was necessary to resort to the 

 tedious process of drilling by hand for a large number of holes on 

 curves, and for rails cut to form closers. 



Sleepers. Wood possesses so many suitable qualities that we 

 can readily understand why it was early selected as the proper 

 material for sleepers. It can be cut to any size and shape, holes 

 can be bored, spikes can be driven, and bolts can be screwed 

 into it without any difficulty and without causing injury to the 

 timber, while the semi-elastic nature of wood absorbs the vibra- 

 tion of the rails and fastenings, and provides a sound-deadening 

 seat so conducive to smooth running. Its only drawback is that 



P 



