Two different types of experiment were reported. Both used a pure single crystal of ice freshly grown in the laboratory at 2 mm per hour.

Direct volumetric measurements were made by submerging an ice crystal (volume 143 cm3) in mercury in a sealed steel container and electronically monitoring the height of the mercury in a manometer tube connected to it. Measurements over a 60 d period at —4.0°C showed a small gradual decrease in apparent volume. This could be due to the adsorption of perhaps 10-2 cm3 of air trapped by the mercury at the surface of the ice. The total un-certainties of the experiment are such that we believe we would have observed a volume dilation of as little as 2.5 × 10-6 per day.

Direct measurements were also made of the change in length of ice samples from the same crystal. One was cut with length parallel to c and the other perpendicular to c. Over a 28 d period, the fractional change in length at —13.7°C was less than 2 × 10-7 per day and less than 7 × 10-8 per day ║c, leading to an upper bound on volume change of 7 × 10-7 per day.

We conclude that if dilation of ice occurs with time, it is less than 10-6 per day and therefore probably not a factor which needs consideration in ordinary experiments.