A large number of organic compounds is known to catalyze the evolution of H2 from solution 1 . This property, which was previously ascribed to N-or S-containing compounds 2 , was recently proved to be exhibited by organo-phosphorus, arsenic and antimony compounds as well 3 . It is related to the ability of a free proton to add to the lone pair of electrons of the hetero-atom. The participation of the cation BH + (B is the catalyst molecule) in the H2-evolution reaction, either as a proton-carrier 4 or as recipient for electrons s ,6, accelerates the rate-determining step and brings about a decrease in the H2 overpotential. The magnitude of catalysis depends both on the acid strength of the cation BH +, as well as on its adsorbability on the surface of the electrode. Under polarographic conditions, a catalytically active substance produces in well-buffered solutions a potentialdependent maximum which grows non-linearly with the concentration of the additive 2 . In non-buffered acid solutions, on the other hand, the same material causes the displacement of the diffusion-controlled H2 wave towards more positive potentials 7-9 .
Holleck and Holieck 1Β° were the first to show that catalytically active material exerts the same property on organic electrode reactions involving the transfer of protons. The polarographic reduction wave of p-cyanoazobenzene in a buffered solution of pH 9.15 was found, for example, to be displaced some 40 mV towards nobler potentials, and to acquire a more reversible character, when the solution was 0.01% with respect to gelatin. Other additives, e.g. N-N-dimethyl-p-phenylene diamine, were found later to exert the same effect 11-13" A number of inorganic electrode processes, e.g. the reduction of oxy-anions, take place with the participation of H + ions. It was, therefore, of interest to establish whether these reactions can be similarly catalysed through the addition of the appropriate surface active substance. Such information is expected to be of value in the elucidation of the mechanism of the electrode process since, if catalysis occurs, the rate-determining step involves the simultaneous transfer of protons. As far as we are aware, no work on oxyanions from this standpoint has been published.
In a study on the kinetics of the polarographic reduction of iodate in aqueous solutions (to be published later) the effect of a large number of surface active agents on the diffusion-controlled wave was tested. Some of these compounds were found to exert catalysis. The curves of Fig. , for example, illustrate the behaviour observed when poly-