The velocity of ice crystallisation through supercooled gelatin gels

It was observed that gelatin gels could be kept for several days at — 3° C. in a supercooled condition. A test-tube containing such a supercooled gel was seeded with a minute piece of ice and, from this point, ice crystals were observed to separate out downwards through the gel. The following preliminary experiment shows that this process occurs at a regular rate:—A solution of gelatin (about 3 per cent.) was poured into twelve test-tubes, of approximately equal internal diameter, which were supercooled by leaving them at — 3° C. for sixteen hours. They were then seeded with ice and, after definite intervals of time, the distance to which the ice crystals had penetrated was measured with a ruler. For each reading the average of the twelve results, was taken, and a curve was constructed (see fig. 1). The distance was plotted against time, and it will be seen that a straight line resulted. The velocity of ice crystallisation in these gels was 5·1 cm./hr., whilst that for distilled water under similar conditions was 1800 cm./hr.