Most of the information presently available on the behaviour of electrolyte solutions is confined to aqueous media at 25 ° C and 1 atmosphere pressure.1We have initiated a programme of work to determine quantities such as electrode potentials, conductances and activities of electrolyte solutions in non-aqueous solvents. In particular, we have studied the mobilities and activities of various ions in liquid ammonia solutions within the temperature range −35° to −70 °C.