296 RAILWAY CONSTRUCTION. 



in working, detract from its efficiency as a quick-acting crane 

 for light weights. 



Fig. 449 shows au ordinary fixed three-ton jib crane, a*very 

 convenient size for general station work. The centre pillar is 

 fixed into a bed of masonry or a solid block of concrete. The 

 jib is of wrought-iron or steel, those materials being so much 

 more reliable than timber, and very little more expensive. This 

 crane must be fixed so that in one direction the jib may com- 

 mand the centre of a railway truck, while in the other it can 

 conveniently raise the packages to or from the carts or loading- 

 bank alongside. In the sketch the crane is shown as placed on 

 the loading-bank, but it may be placed on the same level as the 

 rails if preferred. Cranes of this type and strength are fre- 

 quently found necessary for the inside work of goods-sheds, 

 where packages of considerable weight have to be handled. A 

 very similar class of jib-crane is constantly made for lifting 

 weights of five or ten tons or more, the different parts being 

 made stronger and heavier to correspond to the weights to be 

 raised. 



Fig. 450 shows a five-ton travelling crane. Although more 

 costly, it has the advantage over a fixed crane that it can be 

 moved about from place to place. It is mounted on a very 

 strong waggon framework, and provided with springs and spring 

 buffers. Instead of moving round a long deep centre, the jib of 

 the travelling-crane is arranged to work round a bevelled metal 

 roller-path laid down on the platform of the waggon, and has 

 a heavy counterweight loaded to correspond to its capacity. 

 Before commencing to lift any weight strong oak blocks or filling 

 pieces are inserted between the tops of the axle-boxes and the 

 under side of main beams of waggon, to relieve the springs of 

 the pressure which would arise from the weight lifted. From 

 the four corners of the waggon are suspended chains carrying 

 gripping-hooks to be attached or clipped round the rails. These 

 gripping-hooks, when firmly secured to the rails, prevent the 

 crane from tilting over, as the weight of the waggon and also of 

 the rails and sleepers are brought into play to counteract any 

 tendency to throw the crane off its proper balance. With the 

 larger size travelling cranes, capable of lifting ten or fifteen tons 

 or more, outriggers of joist or I-iron, moving in slides, are run 

 out at right angles on either side, and can be loaded with bars of 

 iron or other weights to form a counterpoise. 



