A mathematical model is developed in Part I of this study for the ionic mass-transfer rates associated with natural convection developing along both electrodes immersed in a CuSO4 aqueous electrolyte. The additional effect of an excess amount of H2SO4 is discussed through the comparisons with the optical measurements. The concentration profiles of both Cu2+ and H+ ions and the natural convective velocity profile have been measured by a two-wavelength holographic interferometer and the tracer method. The present calculation quantitatively agrees with the measured ionic mass-transfer rates toward the electrode surface except for copper electrolysis in an unsupported CuSO4 electrolyte above one-half of the limiting current density. The optical observation suggests that a substantially steady state is attained within 180 s after starting the electrolysis in every case. The numerical calculation predicts a further development of ionic mass-transfer phenomena over 600 s. It is closely related to both secondary flow and electrolyte stratification phenomena.