of the Surface Layers of Liquids. 271 



often asserted that the surface-layers of a liquid are in a 

 state of compression *. According to Lewis f, who has 

 developed a quantitative theory of this supposed surface 

 compression, the variation of the densities of two im- 

 miscible liquids in the neighbourhood of the surface 



Fig. 7. 





i 









\ m 





:> 





1 





»o 









— 









to 









£ 









o> 









Q 









Posit i ion. 



separating them is as shown in fig. 7. In the case of 

 water it is calculated that the mean density in the surface- 

 layer is about twice that in the body of the liquid. An 

 effect of the same order of magnitude is calculated for a 

 number of other liquids. In the exceptional case of mercury 

 the mean density in the surface-layer is only *84 of the bulk 

 density. 



Let us examine this theory of surface compression in the 



* See, for example, ' The Chemistry of Colloids,' by W. W. Taylor 

 (Arnold, 1915), pp. 229 & 250. 



t Phil. Mag. Sept. 1910, p. 502 ; Kolloid-Zeitschrlft, vol. vii. p. 197 

 (1910). 



