﻿Liquids wider Capillary Pressure. 1157 



viscosities at 20° C. have been determined with accuracy, 

 e g. water and chloroform. In the other cases, with the 

 possible exception of benzene, the variations in ihe values 

 of the determinations by various investigators for these 

 quantities is sufficiently large to account for the dis- 

 crepancies. 



A few experiments were made on the rate of penetration 

 of ethyl alcohol water mixtures, when the following values 

 for the penetration coefficients were obtained : — 



Per cent. r _ . Tr , 



Ethyl alcohol. K obs ' K calc - statlC - 



11-40 11-31 



20 5-6 6-2 



40 51 4-9 



60 50 4-6 



80 5-4 5-07 



100 5-65 5-52 



It will be noted that a minimum is obtained at ca. 50 per 

 cent, in agreement with the calculated * values ; but the 

 discrepancy between the calculated and the observed values 

 is considerably greater than the experimental error. 

 Data are lacking on the dynamic values of the surface 

 tensions of alcohol-water mixtures ; but these figures, in- 

 cluding some experiments on the rate of flow of dilute soap 

 solutions, indicate that the surface film in the capillary tube 

 is being continually renewed during its progress through the 

 tube. The method is consequently applicable to the deter- 

 mination of dynamic surface tensions of mixtures which 

 frequently differ considerably from the stated values. 



The penetration coefficient of a liquid is a physical con- 

 stant of importance in that it is related to similar constants 

 for gases and solids. Determination of the Maxwellian 

 period of molecular relaxation in gases (Jeans, ' Dynamical 

 Theory of Gases/ p. 261; Boltzmann, Vorlesung ilber Gas 

 TJieorie, pt. 1, p. 167) or the " sensibilite" of Perrin (Ann. 

 de Pliys. xi. p. 21 (1919)) indicates that the molecules, even 

 when acted upon by the mutually relatively feeble forces of 

 adhesion in the gaseous state, are highly damped, the re- 

 laxation period for nitrogen at 0° C, and 760 mm. being 

 1'66 10~ 12 sec. In the case of solids, the force fields or 

 adhesion forces are naturally much greater, causing the 

 molecular vibration to be even more highly damped. For 



* Dunstan, J. C. S. lxxxv. p. 824 (1904): Firth, J. C. S. xxxiii. 

 p. 268 (1920). 



