Evolution of Heat by Pitchblende. 323 



After the conclusion of this experiment some water un- 

 fortunately got into the calorimeter owing to the failure of a 

 rubber tube. This caused the powder to cake so that it could 

 only be removed by washing it out with water. The wet 

 powder was placed in a steam oven, where it was left for a 

 fortnight, being occasionally stirred to expose fresh surface. 

 The calorimeter was carefully dried out, absolute alcohol 

 being used, and the couple (which was not encased in glass) 

 and the pitchblende were inserted. 



A stream of carefully dried air was then passed through 

 the calorimeter. This air before entering the calorimeter 

 was bubbled through H 2 S0 4 and then passed through four 

 tubes containing solid NaOH, CaCl 2 , and P 2 5 (two tubes). 

 The current was passed for about eight hours a day for four 

 days. Finally, the air was displaced by nitrogen passed 

 through the same drying tubes and the calorimeter closed 

 and buried in the ice. The calorimeter contained 538*5 grms. 

 of pitchblende. 



As will be seen from the chart (No. 2) the temperature at 

 first showed a tendency to become steady at about the same 

 value as before, but after some rather large fluctuations 

 eventually fell rather quickly to about 4*7, where it remained 

 for a fortnight. The experiment was then discontinued. 



The mean temperature for the last 35 days of the experi- 

 ment is 5'45 scale-divisions, but the mean of the last 18 days 

 is only 4*7. This looked as if some chemical heating was 

 occurring at the commencement which subsequently ceased. 



To test this conclusion the calorimeter, which had never 

 been opened, was again buried in the ice three weeks after 

 the conclusion of the last experiment. The temperature 

 variations are shown on the chart (No. 3). The mean foi 

 the last 3G days is 5*85, so that the low readings at the end 

 of the previous experiment are not confirmed, and must 

 probably be ascribed to some irregularity in the temperature 

 of the ice in the neighbourhood of the outer junction of the 

 couple. 



As all these experiments give values for the rate of evolution 

 of heat considerably greater than was to be expected we must 

 consider the most likely sources of error. 



Sources of Error — Chemical Action. 



The most obvious source of error is the possibility of 

 chemical action which would cause too high a result. It is, 

 however, difficult to explain the high results obtained in the 

 foregoing pages by this means. One experiment lasted 



Y2 



