322 



Mr. H. H. Poole on the Bate of 



desiccator for a month, while water-cooling experiments were 

 being made. It was then inserted in the calorimeter and a slow 

 stream of nitrogen, prepared from NH 4 C1 and NaN0 2 , and 

 dried by passing through two P 2 5 tubes, was passed through 

 the calorimeter to expel the air and remove an)- free water 

 which might still remain in the powder. This was continued 

 for five or six hours and then the neck was plugged and the 

 calorimeter buried in planed water-soaked ice. After about 

 a fortnight the temperature became approximately steady 

 and continued so for two months, at the end of which time 

 the experiment was discontinued. The variations of tempe- 

 rature during this interval are plotted on the chart (No. 1). 



The mean reading was 7*1 scale-divisions, and as there were 

 539*8 grms. of pitchblende in the calorimeter we find the Heat 

 Evolution = 7*1 x 10~ 5 calorie per hour per gram of pitch- 

 blende. 



In order to ascertain whether the presence of air had 

 much effect the couple was removed from the calorimeter 

 and the nitrogen expelled by blowing in undried air with a 

 cycle-pump. In order to make the couple stiff enough to be 

 again inserted and to penetrate the pitchblende it had to be 

 enclosed in a glass tube. Otherwise no change was made in 

 the arrangements. At the end of a week the temperature 

 became steady and remained so for a month. The mean 

 deflexion was 9'4 scale-divisions. 



