530 Prof. A. B. Macallum. Acineta tuberosa : [Feb. 19, 



where S is the surface excess per unit of surface area of the part affected, 

 C the concentration of the solute throughout the fluid, a the surface 

 tension value, * R the gas constant, and T the absolute temperature.* 



The value of S as experimentally ascertained was in a great many 

 instances very small. Forch (3) found that in a normal solution of sodium 

 chloride, which raises the surface tension of water, the deficit in the surface 

 film was - 024 mgrm. per square metre. • Whatmough (16) with a normal 

 solution of acetic acid, which lowers the surface tension of water, determined 

 the surface excess to be - 2 mgrm. per square metre, and this concentration 

 increases by less than 15 per cent, even when the concentration of the acid 

 throughout the system was increased eight-fold. Milner (13) estimated that 

 in a sodium oleate solution of 0'00204 gramme-molecular strength the surface 

 concentration of the sodium oleate was 0"4 mgrm. per square metre over 

 that of the solution generally, but from the data furnished by Eeinold and 

 Kucker(15) regarding the conductivity of films made from a solution of 

 1 part of sodium oleate in 60 parts of water, Milner estimated the surface 

 excess therein to be 2"4 mgrm. per square metre. The results of Benson (1) 

 obtained with aqueous solutions of amyl alcohol of - 0375 molar value gave 

 a considerably higher value, the surface excess of amyl alcohol reaching a 

 concentration of 0'0394 molar value, involving an increase of about 5 per cent. 



Were these the only values to come into consideration, surface concen- 

 tration, as a result of the action of surface tension, would be negligible, 

 except for the solution of certain problems of very limited interest. There 

 are, however, other experimentally determined values which make it plain 

 that surface concentration is, under certain conditions, a very great factor in 

 influencing the distribution of salts in solutions. 



These values were recently determined by W. C. M. Lewisf (6, 7, 8) who, 

 to ascertain them, employed ingeniously devised methods. The surfaces on 

 which the condensations were studied were those of aqueous solutions in 

 contact with hydrocarbon oil or with mercury. The oil or mercury was in 

 the form of droplets or spherules of uniform size, the surface area of each of 

 which was calculated from data derived from the total quantity of oil or 

 mercury used and the total number of droplets or spherules formed. The 

 hydrocarbon oil and the mercury were employed because they do not absorb 

 or dissolve in themselves a trace of the solute from the solutions bathing the 

 surface of the droplets or spherules. 



* For the development of this formula from the original values of Gibbs see S. R. 

 Milner, op. cit. 



t From the Muspratt Laboratory for Physical Chemistry of the University of 

 Liverpool. 



