Probable mechanism of the effect of thermal history of solution on the metastable zone width

The metastable zone width of an aqueous solution of FeSO 4 has been measured as a function of the temperature of solution overheating. For the solution overheated to a temperature lower than that of hydrate transformation, the data fit to a continuous, smooth curve, while points obtained in overheating the solution above the hydrate transformation temperature lie distinctly above the extension of the curve. Of hypotheses advanced in the literature to explain the thermal history of solution, only that based on redistribution of subcritical cluster sizes of crystallizing substance seems compatible with the observation.