90 Journal of the Mitchell Society. [fune 



using the corrected data and find no material change in the 



results or conclusions there expressed. ) 



8 P 

 For comparison with these values the -^7= can be calculated 



from any equation connecting vapor pressure and tempera- 

 ture. Of the numerous equations that have been proposed 

 the one usually known as Biot's has proved by far the most 

 serviceable. It takes the form, 



[6] Log P = a+b.at + c.p t . 



By differentiating and changing to Naperian logarithms we 

 g-et, 



[7] ]^ = 5.3019 P(£. log a. a<+£. log /^/?). 



Since we had previously used Biot's formula for calculating 

 heats of vaporization more directly, we found it easier to 

 throw equation 7 into the form, 



[8] -^- = .031414 PA, 



where, A = 168.775 (3 . log a . a< + c log /3 . j3*). The constants 

 for this equation have already been given 1 for all of the sub- 



iJour. Phys Ohem., 8, 383 (1904). 

 stances examined except those noted below. 



A = antilog (1.9882227 - .00172541/) 



+ antilog (L7399799 - .00869664), 



A = antilog (1.4256719 + .0001302029/) 



-I- antilog (0.1799122 — .00410411/), 



A = antilog (1.5561254 - .00011584/) 



+ antilog (.2.51667 - .00400204 /), 



A = antilog (2.3965216 + .003377538/) 



+ antilog (0.3342413 - .00317576/), 



Ethyl oxide. 



/ = /° C. 



Benzene. 



/ = /° C. 



Methyl alcohol 



/ = /° C. 



Ethyl alcohol. 



/ = /° C. 



