HIGH AND LOW TEMPERATURE TESTS. 



267 



mixture used by Mr. Andrews consisted of two parts by 

 weight of snow or powdered ice and one part of salt, while 

 the heating was effected by exposing the axles in a bath of 

 warm water. In some more recent tests at Cornell 

 University a bath of alcohol was used, into which was 

 sprayed liquid carbonic acid, by which means a tempera- 

 ture as low as 70 deg. below zero Fah. could be maintained. 

 Experiments to the same end have been made by M. 

 Knut Styffe, of Stockholm, Mr. Sandberg, Mr. Webster,* at 



1-5 



1-0 



10 



20 



Tons. 



30 



FIG. 131. Load Strain Diagram for Steel Bar, Tested at 650 deg. Fah, 



the Watertown Arsenal, the Berlin Testing Laboratory, 

 and a number of other laboratories. The published results of 

 these tests accord fairly well, and show that wrought iron 

 after slightly decreasing in strength to about 250 deg. Fah. 

 reaches a maximum of strength at about 500 deg. Fah. r 

 and from this point steadily decreases in strength as the 

 temperature is further increased. Steel exhibits much the 

 same properties, reaching a maximum of strength at some- 

 where about 500 deg. Fah. Copper and the bronzes 

 decrease in strength continuously as the temperatures are 

 increased. 



The effect of a high temperature on wrought iron and 

 steel bars under a tensile test is curious as regards the 

 extensions. Whereas, at the normal temperature, the 



* Min. Proc. Inst. C.E., Ix. 



