﻿Bate of Evolution of Heat by Orangite. 191 



no regular change in the deflexion was noted, the fluctuations 

 that occurred being apparently independent o£ the repackings. 

 This is also an argument against the entry of heat into the 

 calorimeter through air-cavities or conduction along the 

 wooden legs. 



As regards the possible loss of heat along the heater leads, 

 these are each 0\195 mm. in diameter and 15 cm. long from 

 the heater-coil to the junction, with the flexible leads in the 

 annular space between the inner and outer Dewar vessels. 

 Assuming that the conductivity of copper is unity, we find 

 that for a difference of temperature of 1° C. between the 

 ends of the leads the flow along the pair is only 0*144 calorie 

 per hour, so for the actual temperature differences involved 

 the flow would be negligible. Moreover, the heating-coil, 

 even when in use, must be at very nearly the same tempera- 

 ture as the rest of the copper vessel, so there is no reason 

 why the heat generated electrically should escape more 

 readily than that produced by the orangite. 



It is possible that the heat-loss may be slightly augmented 

 during the periods that the heater is in use by increased 

 evaporation from the cotton-wool used to plug the mouth of 

 the heater-tube. This probably contains some moisture and 

 may be raised slightly above the temperature of the rest of 

 the copper vessel by the action of the heater. As, however, 

 the evaporated water could only condense on the inner 

 surface of the outer Dewar vessel, it is hard to see how any 

 relatively important increase in the heat-loss could occur in 

 this way, 



Conclusion, 



The apparent decrease in activity observed in the second 

 series of experiments is probably spurious, as the rate of 

 decrease is much greater than that obtained by comparing 

 the first and second series. It is probably due to irregularities 

 in the ice temperature, as already suggested. The mean 

 evolution of heat in the first series is 25'4 x 10~ 5 , and in the 

 second 19*4 xlO" 5 calorie per hour per gram. There seems 

 to be little doubt that this heat must be generated by th 

 orangite. The orangite is from Arendal, Norway, and 

 estimation by the radioactive method indicated the presence 

 of 36 per cent, of elemental thorium. Now Pegram and 

 Webb obtained a value 2*1 x 10~ 5 calorie per hour per gram 

 of thorium oxide in radioactive equilibrium, and this value is 

 much more nearly in accordance with radioactive theory than 

 the very large values obtained in the present experiments. 



The only possible explanation appears to he that the 



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