On the Surface Heat of Charging

Calculation of the surface heat of charging for pure metals, for oxide coated metals and for monatomic films.---Two methods are pointed out for calculating the theoretically necessary reversible heat development or absorption accompanying the charging of the surface of a conductor. One method depends on a new relation ηₛ₁-ηₛ₂=kTln(A₁A₂)+εP₂₁ between the surface heats, ηₛ, of the two surfaces, the A's of electron emission equations of the type i=AT²ε^-b/T and the Peltier heat at the interface between the conductors. The other method consists of a comparison of the cooling effect of electron emission and the latent heat calculated from the temperature variation of emission. Experimental evidence points to ηₛ=0 (nearly), $A=60.2$ amps/cm² deg² (nearly) for all pure metals. Oxide coated filaments present a difficulty. For monatomic films the first method gives appreciable values of ηₛ and experimental data for use in the second method is lacking.Stopping potentials of Na, K and Li yield further evidence that ηₛ is very small for all pure metals. The relation between surface heat of charging and certain assumptions fundamental to electron emission theory is discussed.