The interfacial (surface) tension, St, (dyne cm), can be calculated by applying the equation of capillary rise method (when the contact angle Ө → 0):<br />
where:
* h (cm) is the height of Hg column above the Hg meniscus in the capillary
* r (cm) is the radius of capillary
* g is the acceleration due to gravity
* d (g cm) is the Hg density
The circuit contains Hg electrode as the ideally polarizable electrode and a reference electrode as the non-polarizable electrode. Thus, when an external voltage is applied, only EM/S of Hg/solution fluid interface is changed.