On the output function in a Ginsburg’s machine

We give the form of the output function in Ginsburg’s machine in which the input and output dictionaries are abelian groups and the transition function is of a special form.     

Sur des solutions maximales de l'équation de translation

Sans résumé

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Dédié à la mémoire de Alexander M. Ostrowski à l'occasion de l'anniversaire de sa naissance     

General characteristics of the copper-based mercury film electrode

The optimum conditions for the preparation, storage, conditioning and renewal of copper-based mercury film electrodes (CBMFEs) are given. The voltammetric results obtained at these electrodes are compared with the predictions of the theory of cyclic and stripping voltammetry at the mercury film electrode, as well as with the results obtained at the silver-based and the platinum-based mercury film electrodes. The advantage of a CBMFE is prolonged life-time, whereas the disadvantages ar the decreased range of usable positive potentials and the possibility of interfering reactions of the electrodeposited metals with the copper substrate or copper dissolved in the mercury phase. The presence of copper has no essential influence on the behaviour of lead and thallium; it affects the behaviour of zinc markedly and that of cadmium and indium slightly. The conditions allowing the minimization of the harmful action of copper on the behaviour of cadmium and indium have been found.     

Determination of thallium and lead in cadmium salts by anodic stripping voltammetry with addition of surfactants to suppress the cadmium peaks

Conditions have been found which make possible the determination of thallium and/or lead in cadmium and its salts without preliminary separation. The electrochemical activity of the cadmium, which usually interferes in the determination of thallium, is inhibited by the addition of 0.01% of polyethylene glycol of M.W. 4000. Thallium is determined by electrolysis at ?0.74 V vs. SCE, in 0.1M EDTA solution: 10^?1M thallium can be determined in the presence of 0.1M cadmium, while copper and lead at 10^?2M and 10^?5M respectively do not interfere. Lead is determined in 0.1M acetic acid containing 0.1% cetyltrimethylammonium bromide (CTAB). The addition of CTAB shifts the cadmium peak, as well as the optimum deposition potential for cadmium, to more negative values, making it possible to determine lead in the presence of cadmium as long as the deposition potential lies in the range between ?0.50 and ?0.56 V vs. SCE. Lead can be determined in the presence of ten times as much thallium.     

Evolution and potential of the BiAS procedure for the determination of non-ionic surfactants

The evolution of the BiAS procedure is reviewed and its standard recommended version was compared with the modified version combined with the indirect tensammetric method (BiAS-ITM). New applications of the use of BiAS-ITM for the determination of nonionic surfactants (in the presence of hydrocarbons or adsorbed on particles) and polyethylene glycols were discussed.     

The determination of traces of thiocyanate and copper(II) ions by cathodic stripping voltammetry

Cathodic stripping methods are described for the determination of traces of thiocyanate ions down to 2 × 10^-8 mol l^-1 and Cu(II) ions down to 1 × 10^-8 mol l^-1. The method involves electrolytic accumulation of copper(I) thiocyanate on the surface of a hanging mercury drop electrode followed by stripping of the deposit during the cathodic scan. For the determination of thiocyanate, a copper amalgam electrode can be used. Examples of application of the method for the determination of traces of thiocyanate in common salts, in saliva and urine as well as for the determination of copper(II) ions in tap water are described.     

Voltammetry at the mercury film electrodes: Comparison of theoretical and experimental results obtained for indium in thiocyanate medium

The voltammetric behaviour of the In(III)-In(Hg) system was studied at the silver-, graphite-, and glassy carbon-based mercury film electrodes under cyclic and stripping conditions in thiocyanate media. The reversible curves obtained at high thiocyanate ion concentration showed a good agreement with theoretical predictions, particularly for the cathodic process. The anodic curves obtained at thin silver-based mercury film electrodes deviated from theoretical predictions due to the interactions between indium, dissolved in mercury, and the silver substrate of the film electrode. At low thiocyanate ion concentrations, where the current was controlled partly by the rate of the preceding chemical step and partly by diffusion, the variations in the film thickness affected the position of the curve as predicted theoretically for the reversible diffusion controlled case.     

Adsorption—Nucleation and growth mechanism of CuSCN monolayer formation on a copper amalgam electrode in thiocyanate solutions

Using voltammetric, galvanostatic and potentiostatic techniques, the electrodeposition of cuprous thiocyanate on a copper amalgam electrode has been studied in acidic solutions containing various thiocyanate ion concentrations. Under the conditions used, the formation of two successive monolayers of CuSCN could be studied before the onset of bulk deposition. It was found that the formation of the first monolayer proceeds according to a complex adsorption-nucleation and growth mechanism. In the first stage, cuprous thiocyanate is adsorbed on the amalgam electrode; in the second, the disordered layer of adsorbate rearranges to form two-dimensional crystalline centres; and in the third stage, these centres grow, completing the formation of the entire monolayer. The second monolayer is formed in a much simpler way, according to a mechanism of two-dimensional, instantaneous nucleation and growth. At high thiocyanate ion concentration, the formation of the CuSCN layer is obscurred by the extensive formation of solution soluble species.     

Silver based mercury film electrode: Part IV. Comparison of theoretical and experimental voltammetric results obtained for cadmium

Using the silver based mercury film electrode (SBMFE) and cyclic and stripping voltammetric techniques the behaviour of cadmium has been compared with the behaviour of lead as well as with the predictions of the theory of de Vries and van Dalen. At the SBMFE with film thickness between 0.1 and 2 μm lead behaves with good agreement with theoretical predictions and only at thicknesses higher than 2 μm some deviations occur due to collecting of the excess mercury at the bottom of the wire electrode. On the other hand even at thin film electrodes the behaviour of cadmium deviates significantly from the predictions of the theory. The height of the anodic peak decreases and its width increases; also the displacement of the potentials of both cathodic and anodic peaks is smaller than the values predicted theoretically. The deviations are caused neither by the formation of intermetallic compounds in the bulk of mercury phase nor by the formation of heterogenous cadmium amalgam; they reflect the interaction between cadmium dissolved in mercury and the solid silver amalgam which is the substrate of the mercury film. Owing to the effect discussed the stripping determination of cadmium at SBMFE is characterized by a lower sensitivity and reproducibility.     

Voltammetric and chronoamperometric investigation of germanium amalgams: Part I. Properties of the homogenous amalgam

Using cyclic voltammetry and chronoamperometry with several anodic steps the deposition and particularly the oxidation of germanium from a HMDE was investigated within pH range 4–12 at Ge (IV) concentrations ranging from 4×10^?7M to 1×10^?4M in the absence of ligands capable to form the complex compounds with Ge(IV) in a solution. It was found that the initially formed product of electrodeposition is a homogeneous, usually supersaturated amalgam. Germanium from this amalgam oxidizes at about 1 V (vs. mercury sulphate reference electrode) or after some induction period, the length of which depends on concentration of Ge(0) in mercury, it begins to crystallize forming heterogenous germanium amalgam. Germanium from this heterogenous amalgam oxidizes in a separate voltammetric peak at more positive potentials. The solubility of germanium in mercury was evaluated on the basis of the oxidation current of homogenous amalgam and the value obtained is equal to (2±0.5)×10^?7M i.e. (1.1±0.3)×10^?7 wt. %. Applying the Stevens and Shain method the diffusion coefficient of germanium in mercury was found to be (1.32±0.1)×10^?5 cm² s^?1.