and Surface Energy. 37 



"prp 



Again, p^ is on the average equal to 3'7 (Young, 



c RT 



4 Stoichiometry,' p. 211), so that^p-^ = V c . 3'7. We have also 



*- c 



the well-known relationship between boiling-point and 

 critical temperature on the absolute scale, namely that 

 %. P ='62T C (Guldberg, Zeit. Phys. Chem, v. p. 376)/ This, 



V 



together with the approximate value 2*7 for -=7-^ , gives us 



*b.p 



in the above equation 



1-4= x 27x3- 7x2-7 



Li l == ~ — £~7T777vo K.ls.p. 



Putting R = 2 calories, we get 



^ = 19-0. 



To obtain Trouton's Rule in its usual form, we may put 

 L^L — RT 6j5 , 

 or L _ Li_ 



Mi — r\\ ~T Li) 



J-b.p ±b.p 



whence L =19 . + 2 = 21 



±b.p 



which is in very good agreement with the mean empirical 

 value 20-22. It thus appears that Trouton's Rule is merely 

 Bakker's equation expressed in terms of the principle of 

 corresponding states, and liquids to which that principle 

 •does not apply approximately may be expected to give 



values for ^ — differing from the mean value 20-22. 



±b.p 



For oxygen at its boiling-point we have : — 



^=1-72, ^=2-17*, ^ = 3-419 f, £* = 1-467, 



1-b.p V b.p ±cVc <Z C 



av hence 7^ — =17*2. By the application of Nernst's modi- 



p . . L 



fication of Clausius' equation, ^ — =18*0 (Nernst, Tlieor. 



Chem. p. 273). U -p 



* From mean value of v c in Kaye and Lab}''s Tables, 

 t Young's ' Stoichiometry.' p. 212. 



* 



