40 Mr. D. L. Hammick on Latent Heat 



Since X ( =X — ^-, we get 



X _ 3x9-81 RT v m 



a 2 ~ d.J + Ma 2 W 



Giving as in (3) the mean value 4*5 xlO -8 to d, the 



3 x 9*81 RT 



molecular diameter, — - 7 — y~ becomes 15*64. Also ^f— r, is 

 a . J Ma" 5 



"R r P Q-Q1 T?T 



equivalent to ^7— X — ^— ; from Table II., ^- is about *35 



Yp . 2 RT V/? 



for organic liquids, so that yr-j is about 1*72. Hence 



-3 = 17*4. Walden's mean value is 17*9. 

 a 2 



Equation (4) is merely (3) altered to provide for the 



expression of surface energy as "specific cohesion." Walden 



has, however, combined his empirical relation -^ with 



Ma 2 a 



Trouton's Rule, and obtained 7ti — =1*2. We can deduce 



±b.p 



this result at once. For Trouton's Rule we have found 

 11 =21 (p. 37) or \ = 21.- 1 bp 



■b.p 



Ma 2 21 

 17*4 has been deduced ; hence rv — = — -=—r =1*3. 



U. P J-'*4 



If the freezing-point can be regarded as being approxi- 

 mately a corresponding temperature, we can obviously 



Ma 2 

 derive Walden's melting-point relationship ^ — = constant. 



The mean value found by Jaeger is 3*65 ; variations from 

 the mean are, however, considerable. Thus for benzene at 

 5°*4 C. the value 1*97 is found. By calculation from Jaeger's 

 data and d = 4:'SS x 10~ 8 cm., we find, on the lines of 



equation (4), -2=15'44 at the melting-point 5°*4 C. 



(288°'4 absolute). From the data : 



^(absolute) = 2-02, - c - =2*94, |^f = 3'755, 



a m . p -05808 . MX OQ . 



whence -^ — tor benzene at its melting-point comes to 1*86. 



^ = 21 (p. 37) or \ = 21.^. For ~ the mean value 



