Since no electrons are being injected into the solution (via Ru(NH3)6 3+ reduction) during this latter 6 second period, it is clear that the translocation of the concentration profiles is due to a selfsustaining reaction. From the shift in the concentration profiles between t = 6 and 12 s, we estimate that the traveling wave velocity is ~18 µm/s. Self-propagating chemical waves are known to be associated with autocatalytic chemical systems, with the chemical wave velocity determined by the kinetics of the autocatalytic reaction.