The streaming mercury electrode technique described by Grahame [3] was used to measure the potential of zero charge (pzc). The solutions were made up in alkaline permanganate bidistilled water from Baker Reagent salts and were deaerated by bubbling nitrogen in the cell before each run. Experimental details have been reported elsewhere [8]. In order to check the experimental behaviour of the system, a 0.1 M solution of KC1 was measured at 25°C, and a discrepancy of only ±0.001 V with Grahame's results was found [3].