Evolution of Heat hy Pitchblende. 59 



the arrangement was about 5 per cent, more sensitive, so 

 that 1° C. corresponded to about 1200 scale-divisions. The 

 chart begins two days after the ice was packed. It will be 

 seen that for a week after packing the temperature difference 



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indicated by the couple in the ice never exceeded 0°'0004 C, 

 and was sometimes in one direction sometimes in the other ; 

 but as time went on the differences and irregularities became 

 greater and greater, the maximum difference of temperature 

 recorded being nearly 0° 0020 C. There can be little doubt 

 that the irregularities observed in the apparent temperature 

 of the pitchblende are to be ascribed to fluctuations in the 

 temperature of the outer junction. These fluctuations almost 

 invariably increase with the time that has elapsed since 

 packing. These variations of temperature may be due to 

 the action of the Mater on the zinc of which the vessel is 

 composed, or to regelation effects ; these points will be further 

 considered later. 



The mean temperature between the pitchblende and the 

 ice for the last 30 days was 8*3 scale-divisons. As the heat 

 escaping from the calorimeter in calories per hour is 6'2 times 

 the temperature difference between the interior and the ice* 



the heat evolution per gram of pitchblende is fiy^r ) '^rp'> 



