The standard molal potentials E°m of the Hg/Hg2(OPr)2, OPr- electrode at 15°, 20°, 25°, 30° and 35° C have been determined. The E°m values obtained are 0.5114, 0.5072, 0.5031, 0.4988 and 0.4942 V respectively, which can be fitted to the equation Edgm/V = 0.5031 -8.56 × 10-4 (itt/°C - 25)-3.0588 × 10-6 (t/ °C -25)2. The changes in standard free energy, entropy and enthalpy for the cell reaction have been calculated. © 1978.