352 Dr. G. Bakker on the 



of fio\ 1. For our case the axis of volume is a tangent to 

 the isotherm, and therefore 



pnq. = 0. 



Further, I put approximately, 



and Vi = 26 = five (van der Waals). 



The equation (20) gives therefore 



Pi ffvap. _ 3v 1 + 2c k 



Pvap. Pi ~ 3V 2 



Hence, 



-^-=1-048. 



Pvap. 



Now Pl = 7896-2 mm. 10*528 X 10 6 dyne per cm. 2 



The equation of Kelvin gives therefore for the order of 

 greatness of the radius of the bubble of vapour of minimal 



size : 



-o 2H 2H 2x5-17 1 A . Q 1A fi 

 R = — = = 1A , OQ x 1-018 x 10- 6 



/'yap. —Pin. Pvap. 10 '52b 



= about 10 -6 cm. = 10 //,//.. 



We find thus a value of the order of greatness of the 

 thickness of the plane capillary layer at the considered 

 temperature. 



Observation I. 



If we calculate the energy required to convert a film of mea- 

 surable thickness at a constant temperature in a film of minimal 

 thickness in the manner, given by Kelvin in his popular 

 lecture " The Size of Atoms/' we shall find for a water-film of 

 1 gramme, which has a minimal thickness of 6 fjbjju ( Johonnott) 

 an amount of work which is equivalent to almost 9 minor 

 cal. When we go on to stretch the film, the state of the film 

 becomes labile,and, if our considerations and calculations above 

 are exact, the most complete crumbling would be attained 

 when the film was converted into spherical drops with a 

 diameter of about 6 fjbfi. 



For the surface of a film of 6 fx/uu (per gramme) we find 

 further 



2 10% 



6xl0- 7 ~ 3 * 



* Because I calculate the order of greatness and not the exact value 

 of the surface, I have taken for the mean density of the film unity. 



