The electrification of frost deposits

Experiments showed that the exposure of a frost deposit to an air‐stream caused ice splinters to be blown away from the deposit. These splinters were negatively charged if the air‐stream were warmer than the deposit, and positively charged if it were colder; if they were at the same temperature then no electrification was produced. In a typical experiment, with the frost deposit 10$C warmer than the air‐stream, the average charge carried away on a frost splinter was 6 × 10−7 e.s.u. These results can be explained, in sign and magnitude, by the Latham‐Mason theory of charge transfer associated with temperature gradients in ice; in the frost‐electrification experiments a temperature gradient was produced down a frost needle owing to the difference in temperature between the air‐stream and the frost deposit, thus causing the outer and inner tips of the needle to acquire equal and opposite charges. If the needle were then broken and blown off by the air‐stream it would carry away a charge of one sign leaving that of the other sign on the frost deposit on which it had grown; the sign of the observed charging was in agreement with the theory. Putting into the temperature‐gradient equations measured values of the dimensions of an ice splinter and the temperature difference between its ends it was possible to calculate the theoretical charge residing on the ends of an ice splinter; this value was found to be in good agreement with the measured average charge per splinter.