I9IS-] 



IN RECENTLY HARDENED STEEL. 



157 



The " Normal Cooling " curve was obtained five or six weeks 

 after the other, and when the generation of heat had very nearly 



Analysis of Steel 

 Phosphorus 0.012 

 Sulphur 0.016 

 Silicon 0.21 



Manganese 0.31 

 Carbon 1.14 



30 



40 50 60 70 5o 100 



Hours After Hardening 

 Fig. 2. 



140 



ceased. For this purpose the steel bars were removed, warmed a 

 few degrees, and replaced ; then galvanometer readings were made 

 from time to time as before. This curve is plotted in a location 

 convenient for visual comparison with the heating curve, but other- 

 wise might just as well be plotted further to the right. 



From the two observed curves I have computed a third cvirve 

 (not shown) which represents the progressive rise in temperature 

 which would have occurred if the thermal insulation of the steel had 

 been perfect, so as to prevent any loss of heat. The curve is 

 strikingly similar in character to the shrinkage curve shown in Fig. 

 5, and indicates a close association of heat generation and shrinking, 

 to which I shall refer again. The total rise in temperature indi- 

 cated (about five degrees C.) is of little quantitative importance 

 because it is highly probable that it would have been different if the 

 steel had been hardened at a different temperature, or more uni- 

 formly hardened throughout each bar, or had a different carbon con- 

 tent. Yet it is interesting to note that the observed quantity of 

 heat spontaneously generated in the steel, measured by its rise in 

 temperature multiplied by its thermal capacity, indicates internal 



