of Gibbs s Theory of Surface- Concentration. 



469 



The Interfacial Tension between a Hydeocaebon Oil 

 and Aqueous Solution of Electeolyte. 



The oil employed was similar to that previously experi- 

 mented with. About twenty electrolytes in all were examined 

 and all showed a lowering effect on the oil-water tension — in 

 general monovalent ions of small atomic weight having 

 least effect while copper and barium salts had a marked 

 influence. This lowering of the tension is remarkable in 

 view of the fact that inorganic salts (with the exception of 

 lithium) raise the air-water tension *. Further, it is a 

 general property of salts to be adsorbed by charcoal ; and if 

 this is regarded as indicative of a lowering of tension at the 

 charcoal surface, one may be perhaps justified in saying 

 that for aqueous solutions of an electrolyte at a liquid or 

 solid t interface, one may expect in all cases a lowering of 

 tension accompanied by adsorption, while on the other hand 

 at the solution-air surface no such generalization can be made. 



A certain number of these salts were selected for adsorp- 

 tion determinations — in the case of caustic soda the emulsion 

 method % being employed ; while with the rest the large- 

 dropping apparatus was used — this being rendered necessary 

 as the adsorption determinations were carried out for each 

 ion of the salt separately the, concentration changes being 

 estimated by ordinary volumetric and gravimetric means. 



Tlie Adsorption of Caustic Soda on Hydrocarbon Oil. 



The values of the interfacial tension for different concen- 

 trations of the base (corrected for density) are summarized 

 in the following table. 



Table I. 



Concentration 



Interfacial Tension in dynes/cm. 



per cent. 



in gram-moles/litre. 











45-81 



10 



0-25 



2693 



2-0 



05 



2249 



40 



10 



16*76 



80 



20 



streaming from orifice of pipette 

 — tension to small to be measured. 



* Whatmougb, Zeitschr. Phys. Chcm. vol. xxxix. p. 129 (1901). 

 t Using the word in its ordinary sense. | See former paper. 



