510 Transition Layer between Two Adjacent Phases. 

 maximum before falling to zero. The water-oil case might 



be represented thus (fig. 1) : 



Fig. 1. 



W*T£K 



« 



0,L 



A £-!--i 



The vertical dotted line represents the imaginary mathe- 

 matical " surface " ; the distance AB represents the thickness 

 of the heterogeneous layer, the horizontal lines representing 

 the constant bulk densities on each side. For the case of a 

 liquid in contact with its own vapour, we obtain (fig. 2) : 



Fig. 2. 



LiQwoWsirsft 



A* 



f] 



Water fapov/? 



The magnitudes denoted by ar s and K s are the average 

 values over the layer as a whole — the actual values over any 

 small portion of layer may be considerably greater or less 

 than these. 



Summary. 



1. The values for the internal pressure in a liquid, as 

 obtained by the Bakker-Dupre method of calculation, are 

 considerably larger than those calculated from van der 

 Waals's equation. A cause for this is sought in the assump- 

 tion that the density in the surface-layer is greater than in 

 the bulk. 



