180 Dr. F. A. Lindemann on the 



one finds, since 



-±*/I 



"2ttV m' 



I 1+^ 



that 



h _ ^? __ , , \ fa 



,/ 2 *1 ^ J-^ 



It is probable, though by no means certain, that — -= i 



at any rate as a first approximation. Further, at high 

 temperatures the expansion coefficient should be proportional 

 to the compressibility k. If one neglects the difference of 



Q 2 T 

 the correction terms ~, which are small in any case* 



and only differ by something of the order - . r p-, one finds 

 for temperatures which are great compared to /3v, 



In lead /3v=95°, T m = 600°, and Ao the most important term 

 is approximately 50,000 cal. On the above assumptions 

 therefore, i. e. taking X ^/ and the chemical constant as- 

 derived above 



'°4;-- 8 (" +1 ¥- 6 )- 



If 8 is 1 per cent, it is seen that the vapour pressure of the 

 lighter isotope should be 5 per cent, greater than that of 

 the heavier at the melting-point and nearly 3 per cent, 

 greater at 1200°. 



The differences in Guldberg and Waage's constant would 

 be of the same order. It is, however, in the affinity as- 

 measured by the electromotive force that the best hope lies 

 of testing which hypothesis is right. As above 



TT T7 RT. Pl RT/, , , 1916V. 

 V y o= log^ = -^ 1-4+-^ S. 



* W. Nernst & F. A.. Lindemann, Zeitschrift f. ElektrocJiemie, xviL 



p. 822 (1911). 



