Evolution of Heat by Pitchblende. 325 



us assume that all the oxygen entering the calorimeter is 

 absorbed ; then to generate the required 9 '4 calories, the 

 evolution would have to be nearly 1800 calories per gram of 

 oxygen. This is almost as much as is generated by the 

 union of one gram of oxygen with one gram of sulphur. As 

 uraninite is essentially an oxide the formation of a higher 

 oxide is the only likely occurrence, hence this evolution 

 seems excessive ; moreover, our assumption that all the 

 oxygen enters into combination is an extreme one. A rough 

 analysis of air which had lain over some powdered pitch- 

 blende in a closed jar for two months indicated that the 

 absorption of oxygen was very small, and indeed could not be 

 detected with certainty. 



It is worth noting in this connexion that in the long ex- 

 periment (chart No. 1) which gave a higher result than 

 either of the last two, there was no evidence of the entrance 

 of air as the vaseline plug was absolutely intact at the end. 



Irregularities in the Temperature of the lee. 



The ice is frozen from the Dublin water-supply. The 

 total solids in this water amount to about one part in 23,000, 

 but the greater part consists of colloidal substances which 

 would not much affect the freezing-point. The chief salts 

 present are chlorides, mostly of Na, Ca, and Mg, there being 

 0-70 part of CI per 100,000 by weight. If we assume that 

 NaCl is alone present in amount equivalent to the total CI 

 we shall over-estimate the lowering of freezing-point, which, 

 on this assumption, will be 0^00074 C. corresponding to a 

 deflexion of 0*85 scale-division. The concentration of salts in 

 the last parts frozen might cause larger variations. This may 

 explain some of the irregularities observed, as the purity and 

 hence the temperature of the water in contact with the outer 

 junction may vary from time to time, but it is exceedingly 

 unlikely that the outer junction was in every experiment in 

 a region considerably below the average temperature. 



Difference of Temperature beween Centre and Surface 

 of Pitchblende. 

 If r be internal radius of calorimeter, 



h be thermal conductivity of pitchblende, 



q be quantity oE heat evolved per second per unit 



volume, 

 6 be difference of temperature between centre and 

 surface when a steady state has been reached, 

 we readily find that 



•-£■ 



