324 Mr. H. H. Poole on the Rate of 



eleven weeks, and in the last two combined the calorimeter 

 was closed for almost four months, yet there was no evidence 

 of any diminution in the rate of heat-generation. Hence it 

 would seem in these two cases that any chemical action 

 occurring must be maintained by the continuous or inter- 

 mittent entrance of air into the calorimeter, as otherwise the 

 action would have diminished considerably towards the end. 



Some estimate can be made of the possible effects of such 

 a cause. When the calorimeter was opened at the close of 

 the last experiment it was inferred from the appearance of 

 the vaseline plug that air might possibly have been forced 

 into the calorimeter by barometric changes and also during 

 the initial cooling, but that absolutely no liquid water could 

 have got in. Also, owing to the plugging arrangements 

 before described, diffusion would seem to.be negligible. By 

 examination of the barograph charts for the period of the 

 last experiment (August 31st-October 19th, 1909) it was 

 found that the total rise of the barometer amounted to about 

 5 inches. 



The volume of the calorimeter is about 160 c.cs., and of 

 this the pitchblende must occupy at least half, so the gas in 

 the calorimeter may be taken as occupying about 80 c.cs. 

 Hence barometric changes would have introduced about 

 13*3 c.cs. The initial cooling from 15° C. to 0° C. would 

 draw in about 4*4 c.cs., making a total of 17*7 c.cs. of air to 

 account for the excessive heat generation. Now, as will be 

 shown further on, the theoretical value for the rate of evolu- 

 tion of heat is 4*4 x 10 -5 calorie per hour per gram of 

 pitchblende, i. e. 23*7 x 10~ 3 calorie per hour for the whole 

 of the contents of the calorimeter. The rate of evolution 



observed in the last experiment was ^ — =31*7 x 10~ 3 

 calorie per hour. 114o 



The difference to be accounted for is therefore 8 X 10~ 3 

 calorie per hour, or a total of 9*4 calories during the 49 days 

 that the experiment lasted. 



Hydration and oxidation seem to be the only likely actions. 

 Now one cubic metre of saturated air at 0° O. contains 4*835 

 grains of water. Hence weight of water-vapour entering 

 calorimeter during the last experiment amounts to 

 4*835 x 17*7 x 10 -6 or 85*5 x 10 ~ 6 gram ; even if each gram 

 of water yielded 840 calories, as much as it would liberate 

 by combining with CaO, the total heat generated would only 

 amount to '072 calorie, so heating due to hydration seems to 

 be negligible. 



As regards oxidation, 3*72 c.cs. or 5'3xl0~ 3 grin, of 

 oxygen entered the calorimeter during the experiment. Let 



