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The opacity of ice formed from water containing dissolved air is due to the presence of bubbles of air in the ice. Both bubble concentration and sizes were found to depend on the rate of freezing. Bulk water saturated with air at 0°C was found to freeze into ice containing about six bubbles per mm3 when freezing proceeded at 0.5 mm min-1 and 300 per mm3 at a rate of 5 mm min-1. Bubbles were formed at the ice-water boundary when the concentration of dissolved air reached a critical value which, for rates of freezing greater than 2 mm min-1, corresponded to a supersaturation ratio of 30. Agitation of the water could prevent the critical concentration from being attained and clear ice then formed.
A. E. Carte (Wed,) studied this question.