58 PHENOMENA, ATOMS, AND MOLECULES 



for the electron emission from tungsten, we obtain 



ln(2.p) = lnv, + (e/kT)(V.-Vi-V), 



(28) 



where Vj is the ionizing potential of caesium, and Vw is the heat of evapo- 

 ration of electrons from tungsten. The values of the contact potential V 

 calculated from Vp in this way are indicated in Fig. 2 by crosses. These 

 points lie on the curve obtained from Vg. . 



This agreement of the values of V obtained by these three methods 

 shows that our theory gives a complete account of the electrical and 



On 



Fig. 2. Contact Potential of Caesium Films on Tungsten against Clean Tungsten. 



chemical properties of moderately dilute adsorbed films of caesium on 

 tungsten. It proves also that the surface of these tungsteh filaments was 

 essentially homogeneous, so that the probability of evaporation of any 

 adatom or adion was independent of the position of the atoms on the 

 surface and was determined wholly from the value of at that point. 



