EVAPORATION OF ATOMS 



377 



Polyatomic layers with nearly saturated vapor 



A matliematical theory of the building up of polyatomic adsorbed layers 

 as the vapor approaches saturation has already been given.^^ This theory 

 should now be modified by assuming that adsorption of an atom in the nth 

 layer can occur only on an underlying group of at least 4 atoms in the 

 (n — i)st layer. A rough estimate of the number of atoms in each layer 

 may be made by assuming that the number of atoms in the successive layers 

 decreases in the ratio i : 62*. Thus a, the total number of atoms adsorbed 

 (in all layers) per unit area of the filament surface, is 



or (53) 



/.7 



/.6 

 1.5 

 1.4 



e 

 1.3 



I.Z 

 I.I 

 1.0 



230 



JOO 



330 



("K"^ 



^00 



^f30 



300 



330 



Fig. 27. Formation of a second layer of Cs atoms (calculated by Eqs. (6) and (53) ) 



for different values of Ho. Arrows give temperature corresponding to saturated Cs 



vapor. Circles give experimental data obtained at n„ = lo^^ 



The rapidly rising portions of the curves in Fig. 10 near Q = 0.95 have 

 been calculated by this equation with values of Ox and Q^ obtained from 

 Eqs. (6) to (10) and (51). 



^^ I. Langmuir, Jour. Amer. Chem. Soc, 60, 1374 (1918). 



