For a single-band conductor where two or more scattering mechanisms are present, each giving rise to a characteristic thermoelectric powerSn and a electrical resistivityϱn the resultant thermoelectric powerS is given, as a first approximation, by\(S = \sum\limits_n {\varrho _n S_n /\varrho } \). Denoting withS0 the characteristic thermoelectric power due to the scattering of the conduction electrons by the boundary atoms, and withSi andϱi the resultant thermoelectric power and electrical resistivity arising from all other scattering mechanisms, one may writeS=S0+ϱi(Si−S0)/ϱ. The thermoelectric powerS and the electrical resistivityϱ of thin layers of potassium, evaporated in a vacuum ∼5·10−9 Torr on a glass substrate at 90° K temperature, were measured at different thicknesses. The variation ofS as a function of 1/ϱ verifies the above mentioned relation. Thus, the thermoelectric power, characteristic for the scattering by potassium boundary atoms can be determined.