SURFACES OF DISCONTINUITY 675 



Hulett: Z. physik. Chem., 47, 357 (1904). 



Dundon and Mack, and Dundon: /. Am. Chem. Soc, 45, 2479, 2658 



(1923). 

 Thompson: Trans. Faraday Soc, 17, 391 (1922). 



Attempts have also been made to measure the change in 

 total surface energy owing to smallness of particle by determin- 

 ing the heats of solution for small and large particles. See 

 papers by Lipsett, Johnson and Maass in the /. Am. Chem. Soc, 

 49, 925, 1940 (1927); 50, 2701 (1928). 



61. Contact Angles. The Adhesion of a Liquid to a Solid. 



Heat of Wetting 



Pages 326, 327 of Gibbs' treatment deal with the derivation 



B 



Fig. 12 



from the very general method, used earlier on page 280, of the 

 well-known contact-angle relation [672]. The double relation 

 [673] is necessary for an edge. Thus if the line of meeting 

 receives a virtual displacement from the edge of the solid along 

 the face of s in contact with A (Fig. 12) so as to allow the liquid 

 B to come into contact with unit of area of this face, the inter- 

 face between A and B is reduced by an area of amount cos a, 

 where a is the angle YXP. (This is' in general actually an 

 increase since a is usually obtuse.) Thus there would be a 



