336 



Dr. G. Bakker on the 



of which the film (black spot) would consist, would be given 

 by a part of the curve HFK (rig. 1). The pressure p in the 

 plane of symmetry having the same value as the vapour- 





Fig. 1. 





A 8 









- "V 







N 





"h 



\ \ 

 \ \ 

 \ \ 

 \ \ 

 \ \ 





*A 



\ \ 







\ \ \ 

 \ \ \ 



\ v \ 





.4. 



-> \ w 



\ \ \^ r. 





U 



\ \ \ ~-.'-«i-& 















- V N *^r' '' *' -''' 





1\ \ i B * y s yy 





\ v ~-*r''' yy 









A, 





pressure, the relation between p and - for the whole film 



would be given by a curve such as in fig. 2 (p. 339), ivhere 

 p and C 4 have the same ordinate. (By this consideration the 

 letter C l of fig. 2 must be changed into K.) Because, how- 

 ever, the values of the ordinates of the curve HFK between 

 the points H and K are always smaller than the vapour- 

 pressure, the curves between p and K (C 4 ) cannot be incom- 

 plete. Hence we conclude : 



A set of films touched by the saturated vapour must be limited 

 by capillary layers, which are complete and congruent with the 

 capillary layer that limits a great bulk of liquid. 



The minimum value of the thickness of a film must there- 

 fore be greater than twice that of the capillary layer. In- 

 deed, if we consider a film as consisting of two complete 

 capillary layers which touch each other in their plane of 



