of Gibbs's Theory of Surface- Concentration, 471 



Experimental Determination of Y : — 



500 c.c. of caustic-soda solution (concentration 0'3Tper 

 cent.) were shaken with 1*075 c.c. of the oil until a uniform 

 emulsion resulted. After emulsification a tension determin- 

 ation showed that there had been a decrease in concentration 

 of 0'003 per cent. The diameter of the emulsion particles as 

 measured in the microscope was on the average 3 x 10 -5 cm., 

 so that the total adsorbing surface was 107500 cm. 2 

 Hence 



r = l*5 x 10~ 7 grm./cm. 2 or 3*7 x 10~ 9 gram-moles/cm. 2 



r (calculated) = 7-5 x 10~ 9 grm./cm. 2 



or 1*9 x 10"-° gram-moles/cm. 2 



The probable error in the experimental result may amount 

 to 25 per cent. A comparison of the observed with calcu- 

 lated values shows once more the considerable discrepancy 

 which exists between them. It should be observed, however, 

 that the absolute value of the experimental determination 

 has fallen from the order 10 -6 (obtained in previous cases) 

 to 10" 7 grm./cm. 2 It should also be mentioned that if any 

 slight trace of acid were present in the oil the adsorption of a 

 base would be considerably altered. 



Re- determination of the Adsorption of Sodium Gbjcocholate. , 



Having obtained a purer specimen of the material than 

 that used in former cases, the values for the tension between 

 the oil and solutions of different concentrations were again 

 determined. There were only small changes noted in the result 

 — the calculated value for the adsorption (at a concentration 

 0*25 per cent.) being 7x 10 -8 grm./cm. 2 , while in the former 

 case the value was about 5 x 10~ 8 . The actual value deter- 

 mined by experiment was from 3*5 to 4*7 x 10 _t3 grm./cm. 3 

 while in the previous case it had lain between the limits 

 3*1 and 5*4 grm./cm. 2 



The Adsorption of Silver JXitrate. 



In the measurements of the adsorption of this substance 

 (and in all subsequent cases) the " large drop " * apparatus 

 was employed. One litre of J molar silver nitrate was pre- 

 pared and about 750 c.c. poured into the tube through which 

 the oil passed in the form of drops (of about 0*3 cm. 

 diameter), and on the surface of these the solute was ad- 

 sorbed. When the oil-reservoir (of 1 litre capacity) had 



* See previous paper. 



