﻿1158 Floiv of Liquids under Capillary Pressure. 



metals, the period o£ relaxation (Langmuir, Phys. Rev. viii. 

 p. 171 (1916)) is in many cases identical with the period of 

 electronic vibration as determined by the ultra-violet radia- 

 tion frequency (10~ 14 sec), whilst for non-metals a close 

 approximation to the relaxation period is to be found in the 

 vibration frequency of the residual rays or natural infra-red 

 vibration frequency (10~ 12 sec.) (Rideal, Phil. Mag. xl. p. 462 

 (1920)). For liquids, it is to be anticipated that the period 

 of molecular relaxation should lie between these values, 

 i. e. ca. 10 ~ 12 sec, the more polar the medium the shorter 

 being its time of molecular relaxation. This period is given 



by the expression t = -A , where r) is the viscosity of the fluid 



and P the pressure. 



In the case of liquids, P is identical with the internal 



adhesional pressure P 2 = — \f(r)dr. Although f(r) cannot 



be evaluated without a knowledge of the nature of the intra- 

 molecular forces, yet it is possible to obtain values for P 



from various sources, such as the — 9 term of van der Waals' 



equation, from the latent heat of evaporation (Stefan, Wied. 

 Ann. xxix. p. 655 (1886)), from the coefficients of expan- 

 sion and compressibility, or from the surface tension of the 

 liquid. In this latter case 



1 7 



- = K- = K' (penetration coefficient) 2 . 



In the following tables are given the approximate values 

 of P, being the mean values of the determinations bv the 

 various methods, and the values of r calculated therefrom, 

 compared with the values obtained from the penetration 

 coefficient. [K being evaluated from the data for ether.] 



Substance. 



Ether 



Chloroform 



Isobutyl alcohol 

 Isopropyl ,, 



Acetone , 



Water 



p 



nospheres. 



T 10 12 . 



Penetration 



coefficient 



K. 



r 10 1 " frc 



1,590 



1-31 



11-38 



(1-31) 



2,200 



213 



8-93 



210 



1,900 



14-7 



3-76 



122 



2,370 



9'4 



410 



10-1 



2,520 



1-32 



1103 



1-41 



18,050 



054 



11-26 



1-35 



