To establish the applicability of the classical Lippmann electrocapillary equation to a polycrystalline gold electrode, the measurements of the derivative of the surface tension (stress) with respect to charge density (q-estance) have been performed, Measurements were carried out in the solutions of the surface inactive perchlorate anions. For all investigated systems, the estansograms revealed characteristic negative shift of the potential of electrocapillary maximum with respect to the potential of zero charge of the polycrystalline gold electrode found by measurements of the differential capacity. The shift suggests the modified (by A. Gokhshtein) electrocapillary equation - partial derivative gamma/partial derivative E = q + partial derivative q/partial derivative epsilon should be used instead of the classical one. The second term in the modified equation appears due to the variation of the charge density of the solid electrode during the elastic stretching process. This term is positive and almost constant for gold electrode near the potential of zero charge and in the potential range E < E-pzc. In this potential range, a positive term could be associated with the influence of the elastic stretching on the electronic dipole layer charge density of gold. At the potentials positive of E-pzc, a second term strongly depends on both concentration of perchlorate anions and pH. This suggests that perchlorate anions appreciably influence structure of the double layer in this potential region.