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result obtained for acetone is thus seen to be compatible with that of simple aldehydes. The actual barrier above the triplet surface origin can only be estimated, as the location of that origin has not yet been determined. In acetaldehyde, the S^Tj separation is 2500 cm"1,13•14 and assuming a similar value for acetone, the

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For reversible electrochemical systems, complete current-voltage curves are calculated for the ring electrode of a ring-disc system ; the equations derived include the effect of passing current through the disc. The equations are obtained by the rigorous application of the proper boundary conditions to the convective diffusion equation. Despite the fact that the surface concentrations on the ring electrode vary with the radius, the results agree with those that would be obtained by the approximate Nernst diffusion layer treatment. The equations are tested for the Ag/Ag+ system and are found to be in good agreement with experiment.The problem of calculating the complete current-voltage curve for a rotating disc electrode has been solved by Levich.1 At the disc electrode conditions of uniform accessibility prevail, i.e., the surface concentration of each species has a constant value over the entire disc electrode. This is not necessarily true for a ring electrode where, although for a reversible reaction the ratio of the concentrations of electroactive species is constant, the values of the individual concentrations may well vary with Y. Hitherto, the calculation of current-voltage curves for such a situation has depended on the approximate Nernst diffusion layer treatment. En this paper the currentvoltage curves for the ring electrode are calculated by the rigorous application of the proper boundary conditions for two reversible systems : system I A & ne+B, system I T mA & ne+B ; in system 11 the activity of A is assumed to be uniform across both electrode surfaces.Throughout the treatment it is assumed that sufficient inert electrolyte is present so that effects caused by the migration of ions in the electric field can be neglected.CURRENT-VOLTAGE C U R V E FOR SYSTEM I For the reversible redox system A&ne+B let the bulk concentrations of A and B be am and bm and let and where C = 0.510 a%-+, and iD is the current at the disc resulting from the electrochemical conversion of A to B or vice versa. We assume that i is positive whenever u = (nr;nFD,@fii,)(a" -a ) = yA(l -alum>, v = -(nr:nFDI;'C%/i,)(b" -b) = yB(l -b/b"),(2.1) (2.2)

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