The empirical quantity defined by \[i=\frac{i_{\text{d},l}}{c_{\text{B}}\ m^{\frac{2}{3}}\ t_{1}^{\frac{1}{6}}}\] the equation where id,l = limiting diffusion current, cB = bulk concentration of the substance B whose reduction or oxidation is responsible for the wave in question, m = average rate of (mass) flow of mercury (or other liquid metal) and t 1 = drop time.