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The crystallization rate of supersaturated sodium sulfate solutions was investigated in the absence of impurities and on introduction of the following additives; sodium chloride, sulfuric acid, sodium bicarbonate, potassium sulfate, zinc sulfate, sodium and potassium acetate, sugar, and gelatin. All of the experiments were performed at a temperature of 7 exp 0 and with sodium sulfate concentration of 21.95%. The crystallization rate as a function of temperature is characterized by the presence of a maximum and a minimum, the positions of which depend on the concentration of the solution. With significant supercooling the crystallization rate does not depend on the temperature and supersaturation, and it becomes directly proportional to the square of the solution concentration. With low supersaturation (less than 12 to 14%) the limiting stage is diffusion, and the crystallization rate depends only on the concentration difference of the supersaturated and saturated solutions. Variation of the viscosity of the solution and dismeter of the vessel has no influence on the crystallization rate. A study made on the effect of adding salts showed that the greatest increase in the linear crystallization rate was caused by sodium acetate. The crystallization rate depends on the pH of the solution, increasing with a decrease in the pH. (ERA citation 06:014483)