1914] William N. Berg 191 



two layers measured against air by Whatmough are due to experi- 

 mental error, according to Antonow. His experimental results and 

 conclusions are practically identical with those of Quincke and 

 Whatmough already quoted. 



For the present purpose these works o£ Quincke, Whatmough 

 and Antonow may be summarized as follows : (i) The surface ten- 

 sion between two partly immiscible liquids is equal to the difference 

 between their surface tensions against air.* (2) If the two hquids 

 are mutually soluble tho not miscible in all proportions, the surface 

 tension between the two layers is less than the above difference, and 

 in some cases (water-phenol, water-isobutyric acid, methyl alcohol- 

 carbon disulfid, etc.) it is zero. (3) Aqueous Solutions of phenol, 

 isobutyric acid and other substances, such as tartaric, citric and 

 oxalic acids, to be considered later, may vary greatly in their con- 

 centration with very little Variation in their surface tension. 



The second class of Solutions to be considered are the aqueous 

 Solutions of organic substances in general. Water has a higher 

 surface tension than any organic liquid. The exceptional physical 

 properties of water manifest themselves here, as in other branches 

 of physics. The result is that, with the few exceptions to be noted 

 presently, practically all Solutions of organic substances have sur- 

 face tensions lower than that of water.^ The general relation be- 

 tween concentration of organic substance and surface tension is 

 illustrated by the following curve for butyric acid and water. 

 Butyric acid is taken as an example ; a very large number of other 

 organic substances depress the surface tension of water in a similar 

 manner. 



The following points about the nature of the curve are of inter- 

 est: (i) A small amount of the organic substance lowers the sur- 

 face tension of water a great deal.^*^ (2) As the concentration of 

 organic substance varies from approximately 20 to 100 per cent., 

 the surface tension remains practically the same. 



8 Vernon (Biochem. Ztschr., 1913, li, p. i) quotes Maxwell to the eflfect that 

 this is not true. But Maxwell's Statement apparently was made before the work 

 of Quincke was done. 



9 Freundlich: Kapillar chemie, p. 58 (Leipzig, 1909). 



'" On the other hand, no amount of any substance can raise the surface ten- 

 sion of water very much. Gibbs : Thermodynamic Studies, p. 321 ; cited from 

 Freundlich, loc. cit., p. 57. 



