156 BRUSH— SPONTANEOUS GENERATION OF HEAT [April 22, 



ference inside the jars which would follow unequal loss or gain of 

 moisture by the felt and granulated cork. A small thin glass tube, 

 flanged at top and closed at bottom, is located in the axis of each 

 Dewar jar and extends from the waxed cover nearly to the bottom 

 of the inclosed copper cylinder. The glass tubes contain the ends 

 of thermo-electric couples of fine constantan, copper and iron wires, 

 one iron-constantan and one copper-constantan junction at the 

 bottom of each tube. The leading-out wires are copper, and connect 

 the thermo-couples with a reflecting galvanometer having the cus- 

 tomary reading telescope and scale. Careful callibration has shown 

 that 55 scale divisions of the galvanometer indicate one degree C. 

 temperature-difference between A' and B', and that temperature- 

 difference and galvanometer deflection are very closely proportional 

 throughout the range used. 



In the following experiment A' and 5' were removed from the 

 Dewar jars and allowed to attain equal room temperature. Twelve 

 half-inch round bars of tool steel, five inches long and with machined 

 surfaces, were hardened by heating to high " cherry-red " in a re- 

 ducing atmosphere of a gas furnace and quenching in cold water. 

 The bars then had a thin and strongly adhering coating of black 

 oxide. They were next stirred in a large quantity of water at room 

 temperature, to acquire that temperature, wiped dry, and oiled with 

 heavy, neutral mineral oil to prevent generation of heat by further 

 surface oxidation, wiped free of excess of oil and placed in the 

 copper cylinder B'. A weighed quantity of water, also at room 

 temperature, just sufficient to equal the steel bars in thermal capacity 

 had already been placed in A'. The whole apparatus was then as- 

 sembled as quickly as possible, and galvanometer readings com- 

 menced within forty-five minutes of the time of hardening the 

 steel. 



The upper curve in Fig. 2 shows the progress of heat genera- 

 tion in the steel bars during the first 150 hours after hardening. 

 A very slow generation of heat was still easily observable at the 

 end of a month. 



It is seen that the temperature of the steel bars was rising rap- 

 idly when the galvanometer readings commenced, and reached a 

 point (nearly 3° C. at the summit of the curve) where gain and loss 

 of heat balanced each other in about 8 hours. 



