Production of Electric Charges on Water Drops

A RECENT communication¹ by Gill and Alfrey implies that we have interpreted the potential differences accompanying the freezing of dilute aqueous solutions as contact potentials. On the contrary, we agree with Gill and Alfrey that ``a contact potential difference of 230 volts seems most unlikely''. We further believe that the implied interpretation is completely untenable, because the observed potential differences cause the flow of currents of the order of 1 µamp. The statement in question is that ``the potential barrier is at the water-ice interface''. This statement was intended to convey that the charge separation occurs at the interface, and that each ion involved in the charge separation must cross a potential-barrier equal in magnitude and sign to the measured potential difference between the ice and water.