A reversible galvanic cell of molten potassium nitrate is described. It is represented by the following scheme: K(1)/KNO₃(l)/NO₂(g),O₂(g)/Pt(s). The theoretical standard emf calculated from thermochemical data for the reaction K(I) + NO₂(g) + ½O₂(g) = KNO₃(l) is in very good agreement with the one deduced from the experimental results. The standard emf of the cell is given by E ° = 5∙440 + 3∙812 × 10^-4T 1n T - 6∙231 × 10^-8T² + 2∙623/T - 5∙156 × 10^-3T.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas