38 Mr. D. L. Hammick on Latent Beat 



For nitrogen, we have : — 



i = l-64, ^=2-05*, J^ =3-421, ^ = 1-32, 



whence ™ — ~ 18*5. Observed (Nernst as above) ^ — = 17G 

 Similarly, for argon : 



rTr -(calc.) = 18-6, observed = 17-3. 



■U.p 



Turning once more to the equation 



GpV 1 



d 



we can derive the ordinary "external" molecular latent 

 heat as 



whence L — RT _ 6 1 



Vp ~d' J' 



or L 6 RT 



Vp " 5J + V/o (oj 



Now according to Walden, ^— is approximately constant 



for a large number of liquids at their boiling-points and 



equal to 3" 64. Looking at the right-band terms of equation 



(3) it is at once apparent that approximate constancy is to 



be expected. The molecular diameter d has the average 



value of about 4*5 x 10 ~ 8 cm. for the common organic 



substances and variations from this mean value are not very 



1RT 

 great. Neglecting: for the moment the term -ft-, which, 

 to © o V/> ' 



with R in calories, is small, we find for ^— the mean value 



RT 

 3*2. When we introduce the term ^- (R in calories, p in 



ergs x cm. 2 ), we find that 3*2 must be increased, on the 

 average, to 3*55. In Table II. results are given of the 



calculation of ^ r V ' -. for a few liquids. 

 Vp (ergs) 



* From v c ou p. 60, Lewis' ' System of Physical Chemistry, and v b p 

 Ramsay and Prugman, J. C. S. lxxvii. p, 1228 (1910). 



