L>I;S 



HIGH AND LOW TEMPERATURE TESTS. 



extensions take place steadily and gradually, producing a 

 smooth load-strain curve, it is noticed that at certain high 

 temperatures the extensions take place suddenly, in jerks, 

 and the free end of the weighing beam of the machine is 

 seen to drop on to the lower stop and remain there for a 

 few moments, as if the maximum load had been reached, 

 when it is again seen to be raised and the bar carry the 

 load as before. On the extensions being measured during 

 the test in the usual way and a diagram plotted, this will 

 have the form indicated on* Fig. 131. As iron and steel 

 have a maximum strength at about |500 deg. Fah., and if 

 .a bar of one of these metals is tested to destruction at about 

 this temperature, it follows that the bar always breaks at a 

 point outside the fluid, that is, if the bar is parallel in form. 



The following tables of flashing points of a number of 

 oils and melting points of alloys may be useful in selecting 

 a suitable one for the heating bath : 



MELTING POINTS OF ALLOYS OF TIN AND LEAD. 



Johnson's "Materials of Construction.' 



