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The effects of physical disintegration (high-energy ball-milling) on the surface properties (specific surface area and cation-exchange capacity) of beidellite and ripidolite are presented and discussed. The milling caused considerable changes in the morphology of the clay, as shown by SEM and surface properties, followed by loss of crystallinity as shown by X-ray diffraction of the treated clay minerals. The transformation of the crystalline into the amorphous phase takes place directly without the formation of intermediate solids different from the starting crystalline and the resulting amorphous phase. Major changes in specific surface area and cation-exchange capacity were produced after 6 min of milling in beidellite and ripidolite clays, with both samples becoming similar after 30 min and maintaining such a state for 300 min of milling.

The electrochemical impedance of anodically grown passive films on glassy metal Fe 80 B 20 in borate buffered solutions, was measured in the range between +0.50 V vs. sce , the potential of surface film formation, and +1.10 V, which is deep in the range of the oxygen evolution reaction (OER). By modelling, numerical fitting, and validation procedure, equivalent circuits in particular ranges of potentials were established. The values of elements of these were determined and their potential dependence analysed. Results of both the experimental and modelling procedures show that: (i) at passive potentials, between +0.50 and +0.70 V, the electrode impedance exhibits pure capacitance behaviour due to the non-separable film, and Helmholtz double-layer capacitance, with a low ion transfer anodic current density, i a ; (ii) at E ⩾ +0.75 V, the pure capacitance model is complemented by surface (adsorbed) state impedance; (iii) at potentials between +0.95 and +1.05 V the impedance data and a steep increase in i a point towards two-step kinetics of the OER, in which surface (adsorbed) states mediate electron transfer. Comparison of impedance data for Fe 80 B 20 with those obtained for Fe indicates a lower rate constant for the formation of surface (adsorbed) states, a different control step and a lower electrocatalytic efficiency for the OER on Fe 80 B 20 .

Anodic films formed by electrochemical passivation of Fe80B20 ribbons in borate-buffer and in acid sulfate solutions, were studied using impedance spectroscopy, in a broad range of frequencies, at potentials within a range of constant passive currents. The impedance data were analysed according to the general, multiparameter electrode admittance equation, which takes into account at the most, four relaxation processes. An insulator or n-type semiconductor barrier layer impedance determines the total electrode impedance of the passive film formed in the borate buffer solution. In acid sulfate solutions, the total electrode impedance is determined by both an ion-conducting inner layer and a precipitated outer layer. The impedance of the outer layer is characteristic for diffusion in a finite length region, coupled with an ion accumulation hindered kinetics at the inner/outer layer boundary at moderate frequencies, and modulation of the outer layer thickness at very low frequencies. In the borate buffer solution, there is negligible influence of boron on the corrosion rate. Films formed in acid sulfate solutions show a pronounced effect of boron, through formation of a more ion conductive inner layer. Higher corrosion rate of the substrate is caused by a higher dissolution rate of the anodic film.

Experimental investigations of corrosion behavior of glassy metal Fesolfco in 1.0 mol dm"3 H2SO4 are described. Results are presented on voltametric and impedance measurements in three distinct anodic potential ranges. Two relaxation processes have been observed and identified: i) a kinetically controlled interfacial charge transfer mediated by adsorption of some intermediate species in the active dissolution range; ii) the same process, but with a blocking effect due to adsorption of the passivating species in the passivation or transition range; and iii) ion migration in a high electric field within the passive layer with adsorption of surface states in the passive range. Using a general impedance of the resistance, the measured impedances have been characterized in terms of parameters of compatible equivalent circuits.

Summary Cyclic chronopotentiometry has been applied in studies of the kinetics of homogeneous chemical reactions coupled to electrode reaction, and as a diagnostic technique for distinguishing between various mechanisms. Working curves, the plots of relative transition time a n vs. the kinetic parameter, were obtained by digital simulation. For the e.c.e. mechanism, which includes the equilibrium constant between the initial and final species, the information obtained from the third transition time is most important. Within the limits of the equilibrium constant K eq of 10 −5 to 10 4 the resolution was obtained either in a 2 or in a 3 for a whole range of probable kinetic parameters. In real experimental conditions one can obtain the rate coefficient for the first order chemical reaction between 0.05 and 200 s −1 . For the e.c.e. and the disproportionation mechanisms, which are quite similar in many respects, the working curves offer a means of distinguishing between these: if there is overlapping in the a 2 points the a 3 points for the two mechanisms are perfectly separated.

Summary The dismutation of uranium(V) in carbonate-bicarbonate solutions has been studied by means of cyclic chronopotentiometry. The aim of the investigation has been to elucidate the actual reaction mechanism. There is evidence from the data on the concentration and pH dependence of the rate coefficients for the dismutation of uranium(V) that the disproportionation reaction is paralleled by an e.c.e. mechanism. The e.c.e. path contributes significantly to the overall reaction rate for concentrations of free carbonate ion of 5×10−3 M and of U(VI) of 1 and 3×10−3 M. For higher concentrations of either the free carbonate or of U(VI) in the bulk of solution the disproportionation is the predominant mechanism. It is difficult, if not even impossible, with the presently available electrochemical techniques, to estimate the relative contributions of either reaction mechanism.

Adsorption of lower monofunctional alcohols from hexane solutions on controlled pore glass was studied using flow-microcalorimetry. Original and silicone treated glass surfaces were compared for their adsorption properties. For butan(1)ol adsorption densities of 0.26 and 0.71 nm 2 per molecule were found, respectively, the major difference in the energetics of adsorption on these two types of surfaces being entropic in nature.

The reduction of Ni 2+ ions at mercury electrodes in acidic perchlorate solutions, at perchlorate concentrations below 0.2 M , is characterized by absence of kinetic control in the preceding step, and by a complex reaction mechanism following the electron transfer. This reaction sequence is known to involve intermetallic compound formation between Ni and Hg and is best described, as shown here, by a parallel second and third order kinetic scheme. Apparent rate coefficients for this kinetic scheme were determined using cyclic chronopotentiometric data and fitting by digital simulation. A linearization test of computed kinetic rate coefficients versus the number of transitions permits quantitative tests of validity of assumptions made.

The electrokinetic phenomenon of surface conductivity was studied for capillaries of pure fused silica and of a borosilicate glass, in water, dilute aqueous solutions of HCl and NaCl, in methanol and acetonitrile. Measurements were done in the temperature range between 5 and 30°C by a dc linear voltage sweep technique at a rate of 0.2 V/sec or less, and with applied polarization voltages up to ±40 V. Surface conductivity was calculated from the total specific conductivity measured by two bright platinum electrodes at the mouths of the capillary and from the specific bulk conductivity of the liquid medium measured by a separate pair of Pt electrodes at the same temperature. Absolute values of the surface conductivity were between 10 −9 and 10 −10 ohm −1 . Energies of activation were calculated from the slopes, S , of log κ vs 1 T curves, observed within a temperature range from 5 to 30°C. The energies E defined as S = E / k were: 45–55 kJ/mole for the borosilicate glass, and 25–34 kJ/mole for fused silica in water, in aqueous solutions, and in methanol. In acetonitrile they were 105 kJ/mole for borosilicate glass and 59 kJ/mole for fused silica. The results were interpreted on the basis of the assumption that protonic conductivity is the predominant mode of surface charge transfer, with the rotation of water molecules in the first liquid layer as the rate-determining step.

The Krka River estuary (Yugoslav Eastern Adriatic region near the town of Sibenik) with its Prokljan basin, and copper as water contaminant) is used to model a management strategy based on the environmental (assimilative, absorptive, receiving) capacity. This estuarine region is faced with conflicting land and sea use activities, such as mariculture for salmonids, and mooring of pleasure boats and yachting. All these activities in the Prokljan region are additional to industrial effluents originating from the industrial town of Knin, and in the particular case of copper, land-based run-off from vineyards. The present level of total contaminant load is still not excessive, but the potential of the estuarine basin for mariculture requires anticipatory restrictions which depend on the extent and nature of activities to be accommodated. The calculation of environmental capacity and the ensuing conclusions are based on the available information on hydrology, physical, chemical and sedimentological pro...

The electrochemical reduction of the uranyl (VI) ion at Pt, gold-plated Pt and Ni-based thin mercury film rotating disk electrodes was studied in sodium carbonate solutions by cyclic voltammetry. The stability of TMF electrodes and reproducibility of voltammetric curves was tested with respect to different amounts of mercury deposited, and mechanical resistivity against film rupture. It was shown that the kinetic parameters obtained using TMF electrodes are independent of the base metal nature, and that these can be used for hydrodynamic conditions up to Re = 6000. Results indicate that data on k s for irreversible reactions, overlapping with reduction of the ion of the supporting electrolyte, can be assessed only to an ultimate precision of ± 30%.

Adsorption was studied of small monofunctional organic molecules on the surface of controlled-pore glass using flow microcalorimetry. Adsorption isotherms were obtained and monolayer coverage and heats of adsorption estimated. The hypothesis is put forward that the adsorbent-adsorbate interaction is predominantly pair specific, and that the relative basicity of the adsorbate correlates best with the observed heats of adsorption per unit surface area. A simple schematic model is advanced to help in the interpretation of the results.

Measurements of electrical conductance and of the thermoelectric force are reported for oriented solid Na-DNA samples with different amounts of adsorbed H2O. It is shown that H2O has a profound influence on the electrical transport mechanism, influencing both the absolute values of conductance, its energy of activation, and the sign of charge carriers. The semiconductor band model, with the adsorbed H2O molecules acting either as electron donors or acceptors, or proton donors, has been used in interpretation of results, and shown to be, at least, in qualitative agreement.

Electrokinetic potentials of several glasses of well defined bulk composition in aqueous electrolyte solutions were computed from streaming current measurements. The composition of the bulk is reflected in the magnitude of the potential and in the shape of the curves relating the electrokinetic potential and the pH of the solution. No differences have been found between the crystalline and the vitreous state of silica. Addition of Al 2 O 3 to the bulk results not in doping effects but rather in surface neutralization making the surface less acidic. Glasses with an appreciable amount of B 2 O 3 have higher negative potentials at the same pH, and the derivatives of electrokinetic potential vs pH show them to belong to a different type of surface than vitreous or crystalline silica. Studies involving controlled pore glasses of various pore sizes have shown the importance of below-the-surface ionic penetration and/or adsorption in the pores in establishing the solid-movable liquid interfacial electrical equilibrium.

The reduction of the nickel(II) cyanide complex in aqueous solutions, with and without an excess of free cyanide, was studied using the techniques of cyclic chronopotentiometry aided with computer simulation. The mechanism of reduction is an e.c.e. sequence, the chemical rate determining step being a dissociation reaction. Superimposed onto this reaction sequence is a fast equilibrium disproportionation reaction. The rate coefficient of the chemical reaction was determined by fitting working curves, generated by numerical simulation of the reaction sequence, to experimental data. In solutions containing an excess of free cyanide (0.1 mol l −1 KCN +0.1 mol l −1 KCl) the rate coefficient of the chemical reaction is κ c =0.34 s −1 P2 for any equilibrium constant of the disproportionation reaction, K , between 10 and 100. Corresponding values for 0.1 mol l −1 KCl solutions, in absence of free cyanide, are: κ c =0.03 s −1 , and K =10 −3 . P2

Flow microcalorimetry was used to study the adsorption of butanol on controlled pore glass (CPG) surfaces. Heats of adsorption and some thermodynamic data are reported for the adsorption process at the original, hydroxylated and hydrated surfaces and for those heat treated at temperatures of 450. 650 and 900°C. It was found that the molar free energy of adsorption is the same, 17 kJ mole −1 for all the surfaces studied. The molar enthalpy and entropy of adsorption are indicative of steric effects caused by water molecules. For surfaces heat treated to 650°C monolayer coverage of butanol is close to 5 molecules per nm 2 , the same figure as reported for the total number of vicinal and isolated silanol groups on the surface of silica.

Surface film formation studies using interfacial impedance are described for electrode surfaces of a Ni+Cr+Fe alloy (INCONEL-600) used extensively in various technological applications, particularly heat exchangers. Its corrosion resistivity and thermal conductivity are known to be strongly dependent on the state of the surface. Studies involved samples m the form of a rotating disk electrode, cyclic voltammetric identification of the active/passive transition, comparison between electrochemically and thermally modified surfaces, and interfacial impedance measurements. It is shown that the surface layer, prepared under increased temperature and pressure (480 kPa and 150 ° C), is passive and resembles the electrochemically grown passive layer obtained at potentials of polarization more positive than −0.2 V vs. SCE using a single, relatively dilute electrolyte, 1 × 10 −2 mol/dm 3 H 2 SO 4 . From the analysis of impedance parameters, it is concluded that an initial faradaic reaction runs in parallel to an adsorption process, both being inhibited successively by the formation of an electrochemically inactive surface film. The analysis of the potential, time and frequency dependence of the complex impedance data is used to indicate the relative contributions of faradaic and adsorption processes to the overall impedance in the active/passive transition of this material.

Summary The reduction-reoxidation mechanism for uranium(VI) in acidic perchlorate and nitrate solutions has been investigated by cyclic chronopotentiometry. By analysis of data for the second and third transition times it has been shown that possibly no single mechanism of either the reduction-disproportionation sequence or the e.c.e. mechanism is solely operative. The low order pH dependence, the negative dependence on ionic strength of the formal rate coefficient for the chemical reaction following electron transfer, and the consistently shorter third transition time with respect to the second, suggest interpretation based on the involvement of polynuclear complexes, on overlapping of reoxidation waves, and on the existence of an e.c.e. mechanism only in the reverse (reoxidation) step.

Batch and flow microcalorimetry were used to study adsorption of aliphatic amines on silica gel, controlled pore glass (CPG), high alumina glass, and surface-derivatized controlled pore glass. The adsorption of basic aliphatic amines is indicative of the acidity of the surface. Silica gel and controlled pore glass show the same average heat of adsorption for butylamine, 35 ± 2 kJ mole −1, but the CPG, in contrast to the silica gel has nearly homoenergetic surface. High alumina glass (17% Al2O3) has a less acidic surface, and the relevant value for the heat of adsorption of butylamine is only 4.7 kJ mole−1. Surface derivatization with a long-chain aliphatic silane (octadecylsilane) produces a highly hydrophobic surface, when water molecules are used as probes. Interaction with butylamine remains strong, as in the original state of CPG. Derivatization with aminopropylsilane yields a basic surface and the interaction with butylamine is weak, showing a heat of adsorption of only 3–4 kJ mole−1. The paper indicates that surface acidity of silica and glasses can be understood only as an interactive process between the surface and the adsorbate.

Sea sediments of various origin have been studied with respect to their electrokinetic potential in seawater of varying salinity. All the sediments tested are negatively charged in seawater and most of them are positively charged in freshwater. Charge reversal occurs between 2 and 6‰ salinity. This could possibly influence the deposition of certain ions and minerals at, or near, river estuaries.

Electrical conductivity measurements were done on samples of solid bovine methaemoglobin of various hydration states. The energies of activation calculated from these data, are discussed with regard to Rosenberg's theory. The lowest value of the activation energy (observed at 35% hydration) corresponds to that of pure water. Using spectrophotometric techniques the interaction of “chromohaemoglobin” (“anhydrohaemoglobin” after Haurowitz) with oxygen was followed in situ. The importance of the shell of hydration for the reversible oxygenation is discussed and a new hypothesis advanced. An festen Methamoglobinen verschiedenen Hydratationsgrades wurden Messungen der elektrischen Leitfahigkeit vorgenommen. Die aus den Mesergebnissen berechneten Aktivierungsenergien wurden im Zusammenhang mit einer Theorie von Rosenberg diskutiert. Der niedrigste Wert fur die Aktivierungsenergie (beobachtet bei 35% Hydratation) entspricht der des reinen Wassers. Unter Verwendung spektrophotometrischer Methoden wurde die Wechselwirkung zwischen Chromohamoglobin (Anhydrohamoglobin nach Haurowitz) und Sauerstoff untersucht. Die Bedeutung der Hydratationssphare fur die reversible Oxygenierung wird untersucht und eine neue Hypothese aufgestellt.

An electronic device is described for the automatic reversal of the current flowing through an electrochemical cell at a predetermined potential. Provision is made for accurate selection and reproducibility of the potential for current reversal with the accuracy of ± 5 mV. In employing fast mercury-wetted contact relays the device has a switching time of 5 msec.

The chronopotentiometric technique has been used in studying the reduction of uranyl on mercury electrodes in sodium carbonate solutions At 1 M of free carbonate no kinetic complications were observed at experimental conditions pertinent to galvanostatic techniques at quiescent solutions. At low free carbonate concentrations (0.10 M ) the electrochemical reduction is followed by a second order chemical reaction the rate of which is dependent on the concentration of the free carbonate ion. The potential-time relation, is a suitable means of studying the kinetics as dependent on the free ligand concentration and on the concentration of the electroactive uranyl ion. The data indicate that the uranyl tricarbonate complex undergoes reduction without dissociation, while the coupled chemical reaction (disproportionation) involves rearrangement in the transition of uranium(V) into the uranium(IV) and uranium(VI) carbonate complex forms.

Summary The investigation of the mechanism of the electrochemical oxidation of uranium(IV) in sodium bicarbonate solutions is described. The investigation of the electrochemical reaction was carried out using the chronopotentiometric technique and is confined to concentrations of uranium and bicarbonate, at which the former is soluble and stable (1–4 mM of U4+ and 0.4–1.0 M NaHCO3). The electrochemical oxidation is an irreversible (β=0.7±0.02), two-electron transfer reaction with an Eτ/4=−0.17±0.01 V vs. SCE for 1 mM uranium(IV) in 1 M sodium bicarbonate. Evidence is given for chemical kinetic steps, preceding the electrochemical reaction, dependent both on the concentration of uranium and of carbonate. A hypothesis of a “deactivation” mechanism, involving competing association-dissociation reactions, is advanced.

Cyclic voltammograms obtained for the reduction and reoxidation reactions of nickel cyanide complex with and without an excess of free cyanide in solution are shown and discussed. These reactions could best be described as an ECE mechanism, accompanied by a fast equilibrium disproportionation reaction between the two Ni(I) complex intermediates.

The electrokinetic properties of nickel hydroxide, prepared by slow hydrolysis from NiCl 2 solutions, were studied using microelectrophoresis and streaming potential techniques. The particles of a stable Ni(OH) 2 colloidal dispersion were found to be negatively charged throughout the pH range from 12 to 3 where electrophoretic mobility measurements were made. The isoelectric points (IEP) were determined by extrapolation of the mobility -pH curves. They were: 1.50 in HCl (variable ionic strength), 1.79 with NaCl, and 2.77 with CaCl 2 as background electrolytes (constant ionic strength). Experiments in the liotropic series of alkali chlorides showed decreasing mobilities at constant pH, and increasing values of the IEPs of 1.64, 1.77, 2.04, and 2.49 at constant, 10 −3 M/l of LiCl, NaCl, KCl, and CsCl, respectively. The IEP of precipitated, washed and dried (100°C in vacuo) Ni(OH) 2 was found shifted to alkaline region: 9.7 in NaCl and 9.4 in CaCl solutions. NiO, produced by thermal decomposition (250°C in vacuo) of these precipitates was found to have the IEP at pH 11.0 in 10 −3 M/l NaCl solutions. The interpretation suggests that the acidic surface OH groups are structural elements of Ni(OH) 2 . Successive dehydration results both in the aggregation of particles and in the appearance of hydrophobic parts of the surface.

The construction and operation of a device for the measurement of the thermoelectI1ic force (Seebeck effect) is described. The device i:s suitable for the work with oriented biopolymer samples (DNA salts) of high resastivity in the temperature range between - 30 °c and + 30 °c.

Relaxation times were measured for the surface tension relaxation of spread and soluble surface films at the water/air interface. Measurements were done in a modified Langmuir trough with a Wilhelmy Pt sensor attached to an electrobalance using surface sweeping rates between 6.4 and 57.6 Hz-1• The relaxation times were determined in the stationary state from the phase angle between the perturbation function (surface sweeping) and the response function (dynamic surface tension). The calculated values for the relaxation times of oleic acid films were between 0.25 and 1.25 s, and were inversely proportional to both the rate of sweeping and to the concentration of molecules in the surface film. For the soluble surfactant, sodium dodecylsulfate, the relaxation times were reaching a minimum value of 0.2 s, at a bulk concentration between 9.1 and 18.3 ~t mol dm-3•

The initial stages of surface oxidation of the Ni-Cr-Fe alloy INCONEL-600 are investigated using cyclic voltammetric and impedance measurements.

The case of a preceding chemical reaction in a chronopotentiometric experimentunder second order conditions was studied by digital simulation and experimental verification. Chronopotentiometry is sensitive enough to distinguish second from pseudo-first order preceding chemical reaction, only when the ligand ion concentration . is less than five times higher than the electroactive metal ion concentration. These findings are based on experiments of reduction of Ti(IV) in thiocyanate solutions.

The influenoe of ionic surface active agents (SAA), represented by some aliphatic straight chain amines and acids, on the zeta-potential of Ag! precipitates has been studied. It has been shown that SAA ions are zeta-potential determining in a narrow concentration region only'. This region is independent of the pl of the solution. In case the sign of charge of the SAA ion is the same as that of the original precipitate there is no marked influence on the zetapotential. Whether the sign of the zeta-potential is determined by the activity of the constituent ions in the solution or by the concentration of SAA ions, the magnitude of the zeta-potential is determined by the sign of charge and concentration of the counter ion only. The total potential difference and the zeta-potential are brought about by two differe nt, independent processes.

A description of an electroosmotic apparatus based on the principle of a micro bubble flow meter is given. Statistical analysis of some results obtained on quartz particles in aqueous and methanolic solutions of potassium chloride is given, the mean standard error beeing about 7%.

Using radioactive t32Eu 3+ a nd 6oco2 + indicato11s the adsorption of these ions on the surface of silver iodide precipitates was measured. The experiments were performed in the equivalency region, from pl 5.5 to pAg 5.5. The measurem e nts indicated a constant amount of counter ions o f about 2 mgequiv .. /gmole of Ag! adsorbed from pl 5.5 to pl 7. At higher pl a gradual d esorption occurs, and at pAg 7.3 the zero point of adsorption i s attained. The adsorbed amount is independe nt of the concentratio n of the counter ion in the solution in the range from the coagulation concentration up to ten times its value. By aging the precipitate or by some other kind of pretreatm e nt the adsorbed amount of counter ions is d ecreased. In addition the zero point of adsorption is shifted from pAg 7.3 to pAg 7.1. Series of experments were performed to establish the adsorption-desorption equil ib11ia of one ion in presence of various concentrations of a second one.

The method originally employed by . Hurd & Hackermann to me asure streaming currents on single capillaries has been modified for measurements on porous diafragms of precipitates. An application of microvolt amplifiers and pressure transducers in connection with chart recorders to record the streaming current - pressure relation is described.

A systematic study of the influence of exchange of ions on the surface of silver iodide precipitates on the elektrokinetic potential (EKP) was undertaken. Examples of the exchange o:f ions of valencies 1 :2, 1 :3, 1 :4, 2 :4 and 3 :4 are given. At higher activity of potential determining ions in solution, at pl= 3, larger changes in the EKP were measured. At the same pl effects of specific adsorption o:f Th4+ were found. The conclusion is drawn, that the exchange of ions at the surface bears no direct, simple relation to the EKP.

E. Lederer i M. Lederer: Chromatography. (K. Balenović) K. Arima, W. J. Nickerson, M. Pyke, H. Schanderl, A. S. Schultz, A. C. Thaysen i R. S. W. Thorne (urednik W. Rom an): Yeasts. Hag 1957. (V. Johanides) Prace Konferencji Elektrochemicznej (Radovi elektrokemijske konferencije), Varšava, 15.-19. listopada 1955. (V. Pravdić)

An attempt is described to determine the charge densities at different layers of the surfaces of glass. Three different techniques were used: the heat-of-immersion technique, the electron spin resonance hyperfine splitting measurements, and the electrokinetic streaming potential or current technique. Estimates of the charge densities at the various interfaces show the structure can be subdivided into the high and low charge portions. The heat-of-immersion technique, looks into the actual solid surface: there the charge density is estimated at in excess of 1014 unit e-charges per cm2• The hyperfine splitting of the 107Ag ESR spectrum assumed due to the electrostatic field at the site of the localized atom position: a charge density of 0.7 to l.3Xl013 is estimated. It is assumed that the Ag atom is localized in the gel-like layer- solution interface. The excess counter-ion charge in the diffuse part of the double layer in the liquid phase is estimated at 3 to 7 X 1012• Thus, the high charge density plane is the interface solid-gel layer. The estimates are based on independent models of the interface structure, widely accepted in literature, although not entirely free of arbitrary assumptions.

Proton conductivity is established in lithium sulfate monohydrate by electrolysis.experiments in the solid state. This effect is discussed in relation to the large amplitude oscillations of the water molecule as evidenced by proton magnetic resonance measurements at different temperatures. The importance of unidirectional chainlike structure of hydrogen bonds in this substance is emphasized, and several implications of the proton conductivity are mentioned.

The purpose of this work was to investigate the possibility of preparation of uranium dioxide by electrochemical reduction of uranium(VI) from alkali carbonate solutions. There are many interesting features in deciding whether or not the electrochemical process is applicable to certain conditions of solution equilibria in the uranium-carbonate system. The study ·of the reduction of uranium(VI) from carbonate solutions has been undertaken to determine the reduction potential-current density relationship, the current efficiency, and the O/U ratio in the precipitated uranium dioxide, for which only scarce data are available in the literature.

It was suggested in a preceding communication1 that protonic conduction may be operative in borax. Coulometric measurements have so far been used twice as evidence for such a mechanism of electrical conductivity. In the case of cetyl alcohol Kakiuchi et al.2 measured the pressure of the gas evolved on the cathode and verified spectroscopically that it was H 2• Decroly et al.8 measured the gas volumetrically (in a capillary) on the cathodic side of an ice crystal.

A streaming potential device for work with dispersed material is described. The use of a vibrating condenser electrometer-amplifier in connection with a paper strip recorder gives the possibility to perform measurements in short time and with small volume of liquid. Statistical analysis of the results on quartz particles of three different sizes in KCl solutions (1 X 10-s to 5 X l0-3 N) is given. The determination of the ~-potential with this device and experimental technique can be performed with a standard error of about 5%.

Oxidation - reduction reactions of uranium(V) and (VI) in sodium and caesium carbonate solutions at high pH were studied using the chronopotentiometric technique. Uranium(V) formed by electrolysis of uranium(VI) at constant potential is stable, its rate of disproportionation negligible. The apparent standard redox potential (uncorrected) of the U(VI) /U(V) couple was found to be - 0.760V vs. S. C. E. in 1 M Na2C03 and pH = 11.5. The uncorrected overall transfer coefficients for the oxidation of U(V) and rereduction of U(VI) were: 0.64 and 0.42 in 1 M Na2C03, and 0.47 and 0.47 in 0.5 M Cs 2C03• The formal rate coefficients for the oxidation and re-reduction of 1 mM bulk U(V), referred to the N. H. E. were: 2.1 X 10-9 and 2.7 X 10-s cm/sec in 1 M Na2C03, and 8.0 X 10-9 and 1.1 X 10 -s cm/sec in 0.5 M Cs2C03• Narrow concentration limits for the solubility of uranium complexes and the relatively low concentration sensitivity of the chronopotentiometric technique render precise quantitative calculations and corrections for double layer effects or counter-ion association rather difficult.

The electrokinetic potential was measured for uranium oxide samples of different atomic ratios O/U, ranging from 2.00 to 2.45. It was found that the differences in the oxidation states correspond to small but significant differences of the electrokinetic potential, with higher values. for lower oxidation states. The reversal of sign has been observed for positive suspensions at pH = 3.3 by the phosphate counter ion. The electrokinetic po tential was found to be independent of the us+ /U4+ ratio in the solution, indicating that these ions are not potentia l determining.

The zero point of the ~potential (streaming potential and electroosmosis) on AgI coagulated with a neutral electrolyte lies in the region between pAg 5.1 and 6.2 in which region it is irreproducible. The shift of the zero point towards lower pAg values is smallest for the 3-valent and highest for the monovalent cations. The ~potential is independent of the pI value between 3 and 9. The change in concentration of the neutral electrolyte from 10-' to 10-2 N lowers the ~potential for a factor of 3 to 4. The relation between the ~potential and the coagulation with neutral electrolyte and the isoelectric coagulation is discussed.