SPONTANEOUS GENERATION OF HEAT IN RECENTLY 

 HARDENED STEEL. 



By CHARLES F. BRUSH. 

 (Read April 22, 19 15.) 



Two or three years ago, when studying the behavior, under cer- 

 tain conditions, of several specimens of hardened tool steel, I ob- 

 served that they all spontaneously generated a small quantity of 

 heat, the amount of which diminished from day to day, but which 

 was observable for several weeks. In each case the steel had been 

 hardened only a few days prior to its use. It seemed highly prob- 

 able that the generation of heat was associated with some sort of 

 " seasoning " or incipient annealing process, perhaps accompanied 

 by slight change of volume, and that it would be most rapid imme- 

 diately after hardening. I resolved to investigate this curious phe- 

 nomenon more fully, but failed to spare the time until a few months 

 ago. This investigation forms the subject of the present paper. 



Fig. I is a diagram of the apparatus employed. A, B represent 

 two large silvered Dewar vacuum jars selected to have very nearly 

 equal thermal insulating efficiency. They are supported in a wooden 

 rack inside a thick copper cylinder C packed in granulated cork in 

 a wooden box E. D is a. paper extension of C, packed with layers 

 of felt by removal of which and the loose copper cover of C easy 

 access is had to the Dewar jars. The copper cylinder weighs 52 

 pounds and its functions are, by reason of its large thermal capacity 

 and high conductivity, to protect the Dewar jars from any rapid 

 change of temperature, and from temperature stratification. 



The box E is surrounded by a much larger wooden box F lagged 

 with a half-inch layer of felt. A long resistance wire is strung 

 back and forth in the air space between the boxes at the bottom and 

 four sides of E. Electric current controlled by a thermostat warms 

 the wire, whereby the temperature of the air space may be main- 

 tained very nearly constant as many days or weeks as desired. A 



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