494 On Gibhss Theory of Surface-Concentration. 



Scmmaey. 

 (1) The adsorption of various substances on a hydrocarbon- 

 oil surface has been measured. The results are 

 collected in the following table : — 



Substance. 



Adsorption per cm. 2 of the substance assumed to be 



in the form of un dissociated salt or in chemically 



equivalent ionic proportions. 



Found value. 



Calculated value. 



Sodium glycocholate. . 



5x10-6 gnn./cm. 2 



7XlO -s grm./cm. 2 



Congo-red 



3-7x10-6 



1-1x10-7 



Methyl-orauge 



5-5x10-6 



1-2x10-7 



Sodium oleate 



10-6 



10-8 



Caustic soda 



1-5x10-7 



7-5x10-9 



Caffeine 



3-7X10-& 



2-4x10-8 



Substance. 



Adsorption of cation per cm. 2 



Adsorption of 



anion per cm. 2 



Found 

 value. 



Calculated 



value. 



Found 

 value. 



Calculated 

 value. 



Silver nitrate 



Potassium chloride . 

 Barium chloride ... 

 Copper chloride ... 



grm./cm. 2 

 2-5X10-S 



5x10-8 



gnn./cm. 2 , 

 4-5X10-9 



1-7x10-9 



3x10-9 



2x10-9 



grm./cm. 2 



2-3x10-9 



1-6x10-9 



1-6x10-9 



2x10-9 



10-9 



note*. 10-8 



2x10-8 



3-5x10-8 



(2) The large discrepancy between observed and calculated 



values for the first four substances is possibly due to 

 gelatinization upon the oil-surface. 



(3) Caffeine obeys Gibbs's law within the limits of experi- 



mental error. 



(4) There is evidence of slight selective adsorption, the 



cation more than the anion, probably due to elec- 

 trical effects, since the oil is shown to be negatively 

 charged, the potential-difference between the oil and 

 water being approximately 0'05 volt, 



In conclusion, I gladly take this opportunity of expressing 

 my gratitude to Professor F. G. Donnan for his advice and 

 assistance in this work. 



