The effect of sodium dioctysulphosuccinate on the differential capacity of dropping mercury electrode in 0.1 M KCl solution is studied. It is observed that at the desorption potential, vigorous directed movement of liquid occurs at the mercury-aqueous interface. This movement is shown to be responsible for the desorption peak in the differential capacity-potential curve.
The cause of the directed movement is further examined. Arguments are given to support the ideas of Doss and Kalyanasundaram, that the movement is caused by the emerging surface of mercury having a different interfacial tension from that of the older surface, and that the shielding effect of the capillary postulated by Stackelberg does not appear to play an important part either in the production of the desorption peak or the polarographic maxima.
It is found that the directed movement of liquid occurs although to a less extent at potentials far removed from the desorption potential. This results is of great significance in that it points at the importance of looking for such movements before interpreting quantitatively the data obtained with a dropping mercury electrode.