010 Mr. W. A. Scoble : Further Tests of 



material which was perfectly elastic to fracture it was neces- 

 sary to harden the bars. Unfortunately a suitable furnace 

 was not available for heating them. The assistance of an 

 experienced tool smith was obtained, and a spread fire was 

 arranged on a smith's hearth. A long iron tube was heated 

 as uniformly as possible in the fire over a greater length than 

 that of a bar. A bar was placed inside the tube, and was 

 frequently moved along it, and rotated, further to ensure 

 uniform heating. When the bar had attained a suitable 

 temperature, about 1400° Fahr., it was removed from the 

 tube and lowered into dilute vitriol. The bar was kept 

 vertical in order to keep it straight ; it was washed later in 

 strong soda water to neutralize the acid from the hardening 

 bath. The temperature of a bar before it was quenched was 

 not measured, it was only judged from its appearance. It 

 was, therefore, unlikely that the bars were of equal strength 

 after hardening, and it was decided to make more than one 

 test on each bar, so that each specimen would afford inde- 

 pendent evidence on the law of failure. 



The Apparatus and Method of Testing. 



The apparatus employed has been fully described else- 

 where*. One end of a bar was supported so that it was free 

 to take its natural slope under a bending load, but it was not 

 allowed to twist. The bar rested on rollers at 30 inches from 

 the other support, and therefore was free to twist at this end. 

 A wooden pulley fitted on the squared end of the specimen 

 and was twisted by means of ropes which carried dead weights. 

 A bending load was applied at the centre of the bar. The 

 maximum shear stress due to the torque was confined to the 

 whole of the outer surface of a bar, and the bending load 

 produced its maximum compressive stress only at the highest 

 point, and its maximum tensile stress only at the lowest point, 

 of the mid-section of the specimen. The test of a bar under 

 combined loading was made first. For a further torsion test 

 one part of the original bar w r as held in two hardened, ser- 

 rated grips, or clamps, bolted together. The clamps were 

 bolted to a lathe bed with the bar just resting on the roller 

 bearing. The squared end of the half bar then carried the 

 torsion pulley as before. When it was necessary to make a 

 further bending test, a part of the original bar was supported 

 on knife edges and loaded by weights applied at its centre. 



* Proc. Phys. Soc. London, vol, *x. ; also Phil. Mag. Dec. 1906. 



