47 G Mr. W. C. M. Lewis : Experimental Investigation 



It will be noted that potassium shows a greater discre- 

 pancy than silver as regards the calculated value. The 

 results are of about the same order as that obtained for 

 caustic soda. 



Estimation of the Adsorbed Chlorine : — 



The surface area of the oil was 10,000 cm. 2 The change 

 in the chlorine concentration was determined as silver chloride, 

 the difference in weight of AgCl precipitate due to adsorbed 

 chlorine being 0*35 milligram. Hence 



r C i= 8 xlO" 9 grm./cm. 2 

 Eepetition gave r cl = 3 X 10~ 9 grm./cm. 2 



These quantities are, how r ever, so small that one is only 

 justified in stating that the adsorption of the chlorine is of 

 the order 10~ 9 grm./cm. 2 



The calculated value is 1*6 X 10 -9 grm./cm. 2 , so that the 

 agreement between calculated and observed is fairly good. 



These results for potassium chloride appear to point (at 

 least as far as the small changes in concentration observed 

 can be trusted) to the possibility of a certain amount of 

 separation of the ions in the process of adsorption, i. e. a 

 preferential cation adsorption. If this is so, it at once suggests 

 some electrical effect taking place which is not taken account 

 of in Gibbs's capillary theory. 



The Adsorption of Barium Chloride. 



In the case of this substance the chlorine only was esti- 

 mated, this being carried out volumetrically with AgN0 3 

 solution. The surface area of the oil was 4000 cm. 2 . In 

 the titration the change in concentration of chlorine due to 

 adsorption was less than 0*1 c.c. AgN0 3 solution. From 

 this one can only say, therefore, that the adsorption Tci is 

 not of greater magnitude than 10 ~ 8 grm./cm. 2 



Calculation of the Adsorption : — 



The following table (IV.) contains the values obtained for 

 the tension (corrected for density) at different concentrations. 



The values of the tension are plotted against concentration 

 in fig. 4. By taking the tangent to this curve the value of 



-^— is obtained for a particular concentration. 



