570 RICE ART. L 



If c is small compared to a 



If A is the area occupied by unit mass of the adsorbed solute 

 then 



FA = Rt, 



since A = T~^. The analogy between this and the Boyle- 

 Charles law is obvious, and exactly the same equation can be 

 obtained by applying to this two dimensional phase the familiar 

 kinetic argument which derives that law for a three-dimen- 

 sional gas. These gaseous films, however, deviate in practice 

 from such an ideal law in the case of larger concentrations for 

 which the approximations used above are no longer valid. Ac- 

 tually the deviations resemble the deviations for gases. Thus 



Rt " da dF 



— = RtV = - 7- = c -7- • 

 A dc dc 



Therefore 



Rt^ _ d logF 

 FA~ d log c 



or 



PA _ d log c 

 Rt ~ dlogF' 



From the tables of c and F (or ao — a), the values of FA/Rt 

 for various concentrations can be calculated and plotted against 

 F. The curves show a resemblance to the {PV /Rt, P) curves 

 for gases. (See Rideal's Surface Chemistry, Chapter II, 



