164 BRUSH— SPONTANEOUS GENERATION OF HEAT. [April 22, 



hardened condition the viscosity was many times greater. This is 

 a further illustration of the instability of the hardened steel. 



In conclusion, I am led to regard the hardened steel as being in 

 a condition of very great molecular strain somewhat unstable, espe- 

 cially at first. Spontaneous relief of a small portion of the strain 

 causes generation of heat until stability at room temperature is 

 reached. Any considerable rise of temperature, as in tempering, 

 permits further spontaneous relief of strain, or molecular rear- 

 rangement, doubtless accompanied by more generation of heat, and 

 so on until annealing temperature is reached. It is obvious that 

 the process of tempering or annealing steel is an exothermic one, 

 and conversely that hardening is an endothermic process. 



Cleveland, 



April, 1915. 



