Evolution of Heat hy Pitchblende. 321 



the calorimeter was estimated at about 6*0, making K = 164*4 

 about. This gives C = 0165. The two earlier experiments 

 gave C = 6*31 and = 6*175, so we may take as a mean 

 (j=z(6'2, i. e. when the calorimeter is 1° 0. hotter than the 

 ice 6*2 calories escape per hour. The oil used was intro- 

 duced in the last experiment only, as it was feared that 

 •distillation up the neck of the calorimeter might increase the 

 loss of heat. It was obtained by distilling common petroleum 

 with a pear still-head and collecting a small quantity of the 

 distillate which came over at 205° 0.: about half a cubic 

 -centimetre was poured into the calorimeter after the intro- 

 duction of the water. Since in the experiment to which the 



above table refers ^ = 0*0375 and #j= — 1*9, we have 



a = *071 scale-division per hour. Hence as 1220 scale- 

 divisions are equivalent to 1° 0. a rise of 0°*0014 0. per day 

 iu the temperature of the ice would account for the negative 



temperatures observed. 



Experiments with Pitchblende in the Calorimeter. 



Five experiments were made with pitchblende* The 

 preliminary one gave an extraordinarily high result. This 

 was probably due to chemical action, as, though the powdered 

 pitchblende was in a desiccator for several days, it may not 

 have been perfectly dry, and was in an atmosphere of air in 

 the calorimeter. This experiment was only continued for 

 .about a month altogether. In this experiment the short 

 stem couple was used. 



hi the next experiment the pitchblende was placed under 

 an air-pump over H 2 S0 4 for several days before insertion 

 in the calorimeter. After insertion of the flexible couple and 

 pitchblende the calorimeter was placed under the receiver of 

 an air-pump which was exhausted and then filled with dry 

 atmospheric nitrogen. This was repeated four or five times and 

 then the neck of the calorimeter was plugged with vaseline. 



About ton days after packing the temperature became 

 approximately steady and remained so for over a fortnight. 

 The mean deflexion on reversal was 9*2 scale-divisions. This 

 corresponds to 0°*0080 C. On this occasion the calori- 

 meter contained 560*7 grins, of pitchblende, so Heat Evolved 



6*2 x 8x 1()- 3 o n in s i ■ i e 



= ir 7uv7 =o JxlU ° calorie per hour per gram ot 



pitchblende. In this experiment the ice was only finely 

 broken and soaked, but not planed. 



Before the third experiment the pitchblende was kept in a 

 Phil. Mag. S. 6. Vol. 19. No. 110. Feb. 1910. Y 



