We present the first quantitative proof of the diffusive character of
the mass transport in thin gap electrodeposition experiments. Applying
phase-shift interferometry for the local determination of the concent
ration held. we demonstrate that the diffusion equation can accurately
describe the mass transport in cells whose gap is less than 50 mu m.
We also show the correspondence of the time evolution of experimental
interfacial depletion profiles along the reacting electrode with theor
etical prediction of a simple diffusion equation.