A nonequilibrium version of measuring the electromotive force during a continuous decrease in the temperature at a rate of 5-7 °C/min is used to study the thermodynamic properties of solid solutions of magnesium in aluminum. The studies show that the abrupt change in the potential of an alloy containing 20-30 mol % Mg at 370-380°C reliably correlates with the decomposition of the solid solution formed at 450°C. © Pleiades Publishing, Ltd., 2009.