358 BRUSH— GENERATION OF HEAT IN STEEL. 



former experiments, with a hardness of 31, was next gradually 

 heated to 554°, allowed to cool slowly to 532° and quenched. It 

 was then purposely brought to a temperature slightly above room 

 temperature and placed in the calorimeter. The progress of cooling 

 is plotted in the curve "49" (fourth quenching). For easy com- 

 parison the normal cooling curve is drawn as a dotted line through 

 the first station of the 4^ curve. Beyond this point the 4q curve lies 

 everywhere helotv the normal cooling curve, showing conclusively 

 that the steel cooled abnormally fast. In other words, there was 

 spontaneous disappearance or absorption of heat in the steel, most 

 notable during the first few hours after quenching. Hardness was 



35-5- 



The result of this experiment is remarkable, and was quite un- 

 looked for. I had expected to find a small generation of heat, if 

 anything. 



The steel was next heated to 562° and quenched. The result of 

 this treatment is shown in the curve " 5(7," with its own dotted normal 

 cooling curve. Absorption of heat is again indicated, even greater 

 than in 4g but somev/hat differently distributed. Hardness was 

 now 34.5. 



Again the steel was heated, this time to 594°, and quenched. 

 Again there was marked absorption of heat. The curve, 6q, was 

 almost identical with ^q, and is not plotted, to avoid confusion of 

 lines. Hardness was again 34.5. 



The seventh heating was carried to 667° for quenching. This 

 was a much larger temperature advance than in either of the pre- 

 ceding experiments, and w'as above the temperature of the third 

 quenching, which was followed by very considerable generation of 

 heat. But now there was very considerable absorption of heat, as 

 shown in curve " yq." Hardness was now 34. 



It should be noted that the quenchings which were followed by 

 absorption of heat were made at rising temperatures which had not 

 been exceeded (except slightly in the case oi /[q) since the steel was 

 annealed. But in the case of third quenching the quenching tem- 

 perature was a falling one, reached by cooling from the much higher 

 temperature of decalescence. I can think of no other cause than 



