HIGH AND LOW TEMPERATURE TESTS. 



265 



time allowance is made for tbe free extension of the bar 

 during the test. The casing is filled with a mineral oil 

 having a high flashing point, this oil being maintained at 

 the required temperature by means of a Bunsen burner 

 placed under the casing. In this arrangement there is no 

 provision for measuring the stretch of the bar during the 

 test, but there would be no difficulty in attaching two 

 small projecting pieces from which the measurements 

 could be taken. In order to preserve the temperature 

 uniform throughout the oil, a perforated stirrer, E, is 

 provided. 



Tensile Test of Locomotive Fire-box Slavs under heat. 



Transverse Section on line X 



For testing of this kind a horizontal machine is much 

 better than one of the vertical type, because it is much 

 more easy to maintain the fluid at the required tempera- 

 ture, when the source of heat can be applied beneath the 

 vessel than when the heat has to be applied through the 

 walls of a vertical vessel, and, moreover, less difficulty 

 is experienced in maintaining a fluid-tight joint, where the 

 bar or the holding shackle passes into the vessel. It is also 

 more convenient to work with a permanently fluid substance, 

 such us mineral oil, than to have to make use of an alloy 

 of lead and tin, which, of course, becomes solid at the 

 normal temperature. Where an alloy of this kind has to 

 be used it will be necessary to melt it in a separate vessel, 



