of Gibbs's Theory of Surface- Concentration. 479 



Calculation of the Adsorption of Cu01 2 : — 



The following table gives the value of the tension 

 (corrected for density of the solution) at different concen- 

 trations : — 



Hydrocarbon -Oil and CuCL. 



Concentration 



in gram-moles 



per litre. 



Pipette 

 Drop-number. 



Tension 

 in dynes/cm. 





 00125 

 0025 

 005 



o-i 



135 



140 

 143 

 147 



154 



52 



49-0 



48-9 



47-8 

 45 -3 



These values are plotted in rig. 3. 

 For a solution of concentration M/50 



c = 0-0027 grm./cm. 2 , 



tier 

 dc 



R 



= 518, 



_ 8-4xl0 7 

 " 51 



Where 51 is the molecular weight at this 

 concentration as determined by Biltz *. 



T = 289 abs 



Hence 



c do- 

 HT ~dc~ 



= 4-0x10"-° gram QuCL 



2 per cm. 



r cu + r cl (found) = 5*5x10" 



' s grin. cm. 2 



We have here once more inequality between observed and 

 calculated values. It should be noted that it is the experi- 

 mental value of r which is always the greater, and there are 

 indications that the cation is adsorbed in somewhat greater 

 quantity than the chemical equivalent of the anion. 



Further determinations with other electrolytes must be 

 undertaken before one could definitely state whether this 

 important fact — the separation of the ions — takes place or not. 



Before going on to discuss in more detail, however, the 

 data already given, the experiments carried out with non- 

 electrolytes will first be briefly recorded. 



* Biltz, Zeit. Phys. Chem. vol. xl. p. 199 (1901). 



