Evolution of Heat by Pitchblende, 319 



the ice. This is borne out by the fact that the greater the 

 precautions taken to bring the ice to zero the smaller was 

 this effect. In the first experiment the ice was only finely 

 broken and then soaked in water for a couple of hours. In 

 this case the water attained an apparently steady temperature 

 of 10*0 scale-divisions, L e. about o, 008 C. below that of the 

 ice. In the second experiment the ice was planed to a fine 

 powder but not soaked, and in the third experiment it was 

 soaked for an hour after planing. The temperatures attained 

 in these cases were —4*0 scale-divisions and —1*9 scale- 

 divisions respectively. 



This effect could hardly persist long enough to greatly 

 affect the pitchblende experiments, and would be greatly 

 reduced by the smallness of the specific heat of pitchblende, 

 but of course would tend to make the results too low. 



In each case the temperature-difference approached its 

 final steady value along a true exponential curve. This is 

 what we would expect from Newton's law of cooling if we 

 assume as an approximation that the ice is rising in tempe- 

 rature at a constant rate. For if a be the rate of rise 

 of temperature of ice in scale-divisions per hour, 6 differ- 

 ence of temperature between junctions in scale-divisions, 

 K thermal capacity of calorimeter and contents, C thermal 

 conductance of calorimeter, 



«(-£-)-"* 



-nf.CO + K*. 

 at 



If the calorimeter finally attains an apparently steady tem- 

 perature l5 



.-. -kJ-C(*-4i). 



If 6' be temperature measured from final steady value as 

 zero so that 



lien 



-<=<*> 



the same eouation as we should obtain for 6 if « were zero, so 



