﻿64 Prof. G-. N. Antonoff on the 



necessarily the same in all directions, and it is therefore 

 necessary to specify the direction in which it is to be applied. 



The question arises now whether it is possible to calculate 

 the surface tension of a solid body. 



For the solid state there is no direct method of determining 

 the surface tension, all methods used for liquids being 

 inapplicable in this case. Some attempts were made to 

 estimate the surface tension of solids from indirect evidence. 

 For example, Ostwald * and Hulett f calculated the surface 

 tension of some calcium and barium salts on a basis of a 

 certain theory from the solubility data. The figure given 

 for the latter is about 4000 dynes per cm. From the point of 

 view of our theory, it seems possible to calculate the surface 

 tension by the use of formula (2) by determining experi- 

 mentally the internal pressure per square cm. of the cross- 

 section, if the molecular structure of the substance in the 

 crystalline state is known. 



At the present time the X-ray analysis throws a light on 

 the above question. 



• For example, according to W. H. and W. L. Bragg, the 

 crystal of rock-salt consists of charged ions situated at regular 

 distances from one another. 



Such a case is somewhat different from the one discussed 

 in my paper {loc. cit.). Here it is necessary to assume that 

 l = d, where / is the length of the doublet and d the distance 

 between them, under which conditions the ordinary inverse 

 square law must hold true. The attraction between the 

 charges in a row is equal to 



where e is the elementary charge, and the value of k is the 

 sum of a series 1 — i + J — i + ^— • • • =0*6931. 



Assuming that the adjacent rows have no effect upon the 

 charges, the expression for the surface tension is of the form 



where p — number of particles per unit volume. 

 For the normal pressure the expression will be 



* Zeit. Phtjs. Chem. xxxiv. p. 503 (1900). 

 t Zeit. Phys. Chem. xxxvii. p. 385 (1901). 



