356 



BRUSH— GENERATION OF HEAT IN STEEL. 



']'/'/° C. One of the bars was quenched at this temperature, and its 

 scleroscope hardness was found to be 74. This may be taken as the 

 hardness of " specimen B " after the first quenching described in 

 connection with the second paper. 



The remaining two bars were allowed to cool very slowly in the 

 furnace until complete recovery of magnetic susceptibility took place 

 at about 660°. Recovery was abrupt in temperature. One of these 

 bars was quenched at this temperature, and its hardness was found 

 to be only 37, which is not much above annealed hardness (31). 

 This seems to me conclusive evidence that true hardening did not 

 take place in " specimen B '' on its third quenching already described 



50 60 70 80 100 



Hours After Hardening 



Fig. I. 



above, although good spontaneous generation of heat followed the 

 quenching. 



The three bars were again heated to complete decalescence and 

 annealed in the furnace so as to leave all twelve bars of " specimen 

 B " in annealed condition. 



Fig. I is the curve sheet of " specimen B." " Galvanometer de- 

 flection " measures temperature difiference, indicated thermo- 

 electrically, between the steel under examination and a thermally 

 equivalent quantity of water, contained separately in silvered Dewar 



