AbstractCoulometric study was carried out according to Lingane to determine the number of electrons involved in the reduction of dipicrylaminate ion on the dropping mercury elctrode. Among the three waves shown in the previous paper, the second wave is most well defined. Therefore,n, number of electrons involved at this step was determined. From thenvalue determined in the present investigation, the mechanism of reduction of dipicrylaminate ion on the dropping mercury electrode was given. The polarographic diffusion coefficient was evaluated fromnand diffusion current constant by using Ilkovic equation.