WILLIAM D. HARKINS 



157 



the surface against the attraction of the surrounding molecules, as a part of its migra- 

 tion into the vapor phase, it seems probable that in surface formation as well as in 

 vaporization molecular kinetic energy would be utilized and transformed into poten- 

 tial energy of the surface. That heat is actually used in the formation of the surface is 

 shown by the thermodynamic equation of Clapeyron, which gives the latent heat (/) 

 of the surface as 



87 



l=-T 



hT 



Fig. S. — The free surface energy (or surface tension) of organic liquids. This equals one-half the 

 tensile work (or work of cohesion Wc) per square centimeter. 



Here I gives the amount of molecular kinetic energy which is transformed into molecu- 

 lar energy of position when i sq.cm. of surface is formed. 



TOTAL SURFACE ENERGY 



The total energy Qi) of a surface is equal to the sum of the free energy (7) and the 



latent heat (/), 



h=y-\-l=y-T 



dy 

 dT' 



In the formation of a surface a part of the energy must be supplied in the form of 

 work in order to give rise to the free surface energy, and a part comes from the kinetic 



