COMPRESSION. 



67 



machine. It will be observed, from what has already been 

 said, that the upper gripping shackle suspended from the 

 knife edge in the beam is at A. The second gripping 

 shackle is attached to the crosshead C, and by it the 

 lower end of the tension specimen is gripped. A tension 

 specimen thus held is shown dotted in the figure. The 

 crosshead C can be raised or lowered by two screws D, D, 

 rotated by means of a worm wheel and worm attached to 



FIG. 25. Arrangement for a Compression Test. 



the handle G. The screws pass into nuts attached to a 

 crosshead, which itself is carried by the ram of the straining 

 cylinder E. So that when the ram is driven out of its 

 cylinder by the influx of the pressure water, the crosshead 

 F, the two screws D, D, the crosshead C, and the lower 

 tension shackle, all move downwards together. The screws 

 are necessary for varying the distance between the shackles, 

 so as to suit specimens of different lengths, and also for 

 tightening the wedges when fixing a specimen in the 

 machine for tesLinsr. 



