522 Dr. G. Bakker on the 



If the pressure is expressed in atmospheres, I have found 

 for ether * : 



Pi 



( T \ 2 

 — jt? = 238f 1— ™-j, T=absol. temp., 



and for the temperature at which the (average) pressure f 

 parallel to the surface of the capillary layer is null : 



T = 0-82 TV 



For this temperature (110°* 7 Cels.) the point F in fig. 4 

 lies thus on the volume-axis, which is in accordance with the 

 calculation of van der Waals, which shows (a conceived as a 

 constant) that at the temperature T = 0*844 T k the volume- 

 axis is a tangent to the theoretical isothermf. For the 

 temperature T = 0*82 T/„ p being null, we have for the 

 thickness of the capillary layer : 



, H surface-tension 



h = — = T r— , 



p 1 vapour-tension 



which gives for ether, 



h = 8'5/JL/A. 



At 110°'7 Cels., I find thus for the thickness of the 

 capillary layer of ether a value of the same order of great- 

 ness as the thickness of the capillary layer of a solution of 

 soap in water at ordinary temperatures according to the 

 measurements of Remold and Rucker. 



§ 4. The Gradient of p 2 and the Relation betiveen the Pressure 

 p 2 and the Density p for a Point in the Capillary Layer. 



While the pressure p>i perpendicular to the surface of the 

 capillary layer is a constant and equal to the vapour-pressure 

 (see above, the end of § 2 ; we continue to consider the 

 capillary layer as plane), the pressure p 2 parallel to their 

 surface has a gradient. We will demonstrate how one can 



find the relation between p 2 and the reciprocal value v=- 



P 

 of the density in a point of the capillary layer. For the 



cohesions resp. in the direction of the lines of force (that is 

 to say in the direction normal to the surface of the capillary 

 layer) and perpendicular to the lines of force (and therefore 



* Zeitschr.f.phys. ('hem. li. p. 358 (1905). 



t van der Waals, Continuiteit der (jus en vloeistoftoestand. 



