Drawbacks of the well-known potential-step method are briefly mentioned. A new method called the cyclic potential-step method is introduced, the essential of which is that a square wave voltage is applied to a polarisable electrode. It is shown mathematically that the current response approaches rapidly to a constant pattern. The derivations presented are free from restrictions concerning the reversibility of the system and the magnitude of the amplitude of the square wave.It is shown that the cyclic potential-step method offers easy means for the determination of the transfer-coefficient (a) and the standard exchange current density ( loo).

It is proposed to interpret cell responses in the Laplace transformed state. Information concerning the electrode reaction can then be obtained from the measured response on the basis of the derived response, both responses being in the transformed state. Advantages of the approach are: (a) interpretation of a measured response may be simpler and more exact in the transformed state than in the non‐transformed state; (b) the tedious inverse transformation of a derived relationship is omitted. The approach is illustrated on two cases of the so‐called potential‐step electrolysis. Methods for the experimental Laplace transformation of a measured response are outlined.

The cyclic potential-step method and the cyclic current-step method are applied to two Red/Ox systems. Values of the standard exchange current density and of the transfer coefficient of both the ferro-ferri system in IM H,SO, and the ferrocyanide-ferricyanide system in 1M KCI are deter-

Abstract-The potential]pH diagram of silver in aqueous ammonium salt solution at 25°C has been calculated and verified experimentally.Calculations were carried out on the basis of the standard potential of the silver/silver-ion couple, the dissociation constants of the silver mono-and di-ammonia complex, and the dissociation constant of the ammonium ion, the total silver and nitrogen content being kept constant. The calculated diagram was verified by measuring the potential of the silver electrode at pH values varying from 2 to 12.The measured diagram agrees well with the calculated one; minor differences (up to 15 mV) occur only in the alkaline range.The establishment of the potential is sufficiently rapid to record the entire diagram on a suitable pen-and-ink X/Y recorder within a few minutes. Accordingly, such a recording may serve well as a lecture demonstration on potential/pH diagrams.R&urn&-Le diagramme tension-pH de I'argent en solution ammoniacale aqueuse a 25°C a Bte calcule et verifie exptrimentalement.Le calcul a ete effect& a partir de la tension standard du couple Ag/Ag+-et des constantes de dissociation de l'ion ammonium et des complexes de l'argent avec une ou deux molecules d'ammoniaque, les teneurs totales en argent et azote &ant maintenues constantes.Le diagramme calcule a tte v&it% en mesurant la tension de I'electrode d'argent a des valeurs du pH comprises entre 2 et 12Le diagramme mesure est en bon accord avec le calcul; des ditferences relativement faibles (jusqu'a 15 mV) ont 6th observkes settlement en milieu alcalin.

A new method, designated the cyclic current-step method, for the evaluation of kinetic parameters of electrochemical processes (especially the exchange current jo) is introduced in addition to the well-known (single) current-step method. Its essential basis is that a square wave current is forced through a polarisable electrode and the voltage response of the electrode is measured.It is shown mathematically that the voltage response approaches a constant pattern when "coulomb-symmetry'' is present and a gradually changing pattern is observed when a departure from coulomb-symmetry occurs. Even when the pattern is continuously changing due to the presence of coulomb-asymmetry the evaluation of jo may be easily achieved.By means of the cyclic current-step method it is easily visualised whether or not the influence of the double layer capacity is negligible. Moreover, the method provides a ready means for the elimination of the ohmic part of the voltage response of the electrolytic cell.