Prévision des courbes de dosage par potentiométrie bimétallique au moyen des courbes de polarisation

The knowledge of polarisation curves permits the interpretation and prediction of the form of the curves obtained by bimetallic potentiometric determination.     

Prévision des courbes de dosages potentiométriques

The knowledge of polarisation curves can be used to explain the facts observed in the neighbourhood of the equivalent point in the course of potentiometric determinations as well as the anomalies presented by certain determination curves.It is also possible to interpret the role of a “potential mediator” during the determinations of oxido-reduction potentials.     

Influence des réactions chimiques préalables sur la forme des courbes de polarisation

Equations have been established for polarographic waves observed while a chemical reaction slowly takes place before the exchange of electrons.The method of calculation is analogous to that already used by one of the authors in the case of polarisation curves relative to the reversible or irreversible systems.The variation of the two half-wave potentials and the limiting densities of current have been deduced. The results have been verified by means of the experimental results of R. brdicka concerning pyruvic and phenylglyoxylic acids.     

Interprétation des spectres d'absorption infrarouges de phosphites et d'hypophosphites métalliques

Résumé L'étude de 15 hypophosphites et de 6 phosphites métalliques en poudre, entre 300 et 3700 cm^–1 permet une interprétation des spectres infrarouges avec la considération des structures moléculaires et la comparaison avec les spectres Raman des solutions. Relativement à ce dernier point, les spectres infrarouges apparaissent beaucoup plus complexes.

---

Summary The study of 15 hypophosphites and 6 metal phosphites in the form of powders, between 300 and 3700 cm^–1, allows an interpretation of the infra red spectra with consideration of the molecular structures and a comparison with the Raman spectra of the solutions. With respect to the latter point, the infra red spectra seem much more complex.

---

Zusammenfassung Die Untersuchung von15 Metallhypophosphiten und 6 Metallphosphiten in Pulverform in dem Bereich zwischen 300 und 3700 cm^–1 ermöglicht eine Interpretation der Infrarotspektren in Bezug auf ihre Molekülstruktur und deren Vergleich mit den Ramanspektren ihrer Lösungen. Dieser zeigt, daß die Infrarotspektren sehr viel komplexerer Natur sind.

     

Interprétation de l'isoréflectance des dépôts périodiques

From the two envelopes of reflectance obtained in the passband of a periodic optical filter, the concept of monochromatic isoreflectance already defined for a single wavelength is generalised to an exended spectral range. A method is proposed to obtain coatings with this property. These coatings are interesting for the design and the manufacture.     

Interprétation de la structure de galaxies entourant le Superamas Local

After numerical simulations by E. Praton, we interpret the Cocoon-like structure observed for the distribution of galaxies around us as an effect of infall velocities onto clusters. In this view structures like the Cocoon (or even like the Great-Wall) could be interpreted as observational artefacts.     

Utilisation des courbes de polarisation dans les dosages électrochimiques: Coulométrie á intensité constante

The conditions for coulometric determinations at constant intensity can be deduced from the polarisation curves; these are choice of current density and auxiliary systems, and possible accuracy of the determination. We have used for this study the results previously obtained for potentiometry at constant intensity.     

Pont électrolytique et électrode de référence pour titrages potentiométriques

A salt bridge and a reference electrode for potentiometric titrations are described.     

Numération et taille des bactéries planctoniques au moyen de l'analyse d'images couplée à l'épifluorescence

The interest of the image analysis procedure is the time-saving in automated planktonic bacterial counting and sizing, with the possibility of manual visual field control at all times. Bacterial biomass (in number and volume) and bacterial projected area histograms were determined with a microcomputer. Performance limits of image-analysed epifluorescence microscopy were: camera sensitivity, considering the very low fluorescence levels on stained bacteria; pixel-μm conversion factor, and the impossibility of the apparatus distinguishing between bacteria and fluorescent small particles. This method is not of interest for counting sediment bacteria.     

Méthode de détermination des épaisseurs de films conducteurs par mesures de résistance de surface

To evaluate the thickness of the layers of a Ti/TiAl₃/Al system, experiments based on surface resistance measurements have been performed. The thickness of each layer is deduced from a comparison among calculated and measured values of resistance. We present here a solution for the simulation of surface resistance and the results obtained with this method on Ti/TiAl₃/Al systems.     

Contribution à l'étude des méthodes de dosages électrotitrimétriques

The author establishes a general equation for the polarisation curve of an oxidation-reduction system taking into account the kinetics of reactions and concentration polarisation, and shows how it can be applied to the interpretation of titration curves obtained by the dead-stop end-point method of Foulk and Bawden and by the derivative method of Reilley, Cooke and Furman.     

Influence de la cinétique des réactions chimiques sur les courbes de polarisation : Application à l'étude des complexes thiocyanés du titane(iv) et du titane(III)

The electrochemical oxidation-reduction of the system titanium(IV) — titanium(III) is slow at dropping mercury electrode in perchloric acid or hydrochloric acid, but becomes rapid in the presence of thiocyanate ions.On the basis of polarization curves, interpreted according to a preliminary theoretical study, the authors conclude that the rapid electrochemical reaction is the following: TiOH.SCN⁺² + H⁺ + e ? TiSCN⁺² + H₂OAn application of the findings to the polarographic determination of titanium is given.     

Etude de la structure des niobotungstates NbnW6—nO−2—n19 au moyen des spectres de vibration

A comparative study of the i.r. and Raman spectra of Nb_nW_6—nO^−2—n₁₉ anions (in the range 1200–50 cm⁻¹) was performed. These anions have the hexatungstate structure with W atoms substituted by Nb atoms. The Nb₂W₄ and Nb₄W₂ compounds have a cis configuration (symmetry C_2υ) and Nb₃W₃ a facial configuration (symmetry C_3υ).     

Analyse qualitative et détermination colorimétrique du cobalt au moyen de la carboxy-2-isonitrosoacétanilide

A new method for the identification and colorimetric estimation of Co(II) with 2-carboxy-isonitrosoacetanilide has been developed. This reagent is specific and its sensitiviness is D = 10^b-6(1:1,000,000). The best possible conditions are indicated for the colorimetric determination whereby Beer's law holds for dilutions to 1,2:1,000,000.     

Étude du mécanisme de polymérisation de l'acide silicique par potentiométre

Ionization and solubility of silicic acid with variation of pH and concentration of silicic acid are studied by potentiometric measurements. Two characteristic points appear on titration plots: the first point occurs at pH = 3 with formation of the ionized silicic acid; the second at pH = 7 is interpreted as revealing monomeric species. Diverse species of ionized silicic acid are in sols between pH = 3 and 7; the sols contain the smallest species of polymer for pH < 6 and show an optimum of polymerization for pH ≥ 6.     

Application de la chélatométrie au dosage des esters et chlorures de mono-esters oxaliques

Esters and chlorides of oxalic mono-esters can be estimated volumetrically. After saponification precipitation is carried out by means of a calcium chloride solution, the excess of which is measured by chelatometry.