Polarography of bismuth in malonic and chloroacetic acid media

The polarographic reduction of bismuth in the presence of malonic acid or chloroacetic acid is quasi-reversible. Bismuth forms only one complex with either chloroacetic acid or malonic acid, the complex having a co-ordination number of three. The stability constants have been calculated from the formal potentials using Lingane’s method and these values are in good agreement with those calculated from the half-wave potentials by the method suggested by Sundaresan and Sundaram.     

Polarography of indium in thioglycollic and ascorbic acid media

The polarographic reduction of indium in thioglycollic acid is reversible whereas in ascorbic acid it is quasireversible. The formal potentials have been determined by amalgam polarography and the stability constants calculated.     

Polarography of indium in glycollate medium

Reversible reduction of indium in glycollic acid has been followed by de polarography and the stability constants of the indium glycollate complexes calculated by the method of DeFord and Hume.     

Polarography of molybdenum in phosphoric acid medium

The polarography of molybdenum in phosphoric acid has been studied. The effects of concentrations of molybdenum as well as phosphoric acid and temperature have been studied. The kinetic parameters and the activation energy for the reduction of molybdenum (V) to molybdenum (III) have been calculated.     

Polarography of europium in aqueous and aqueous methanolic solutions

The standard rate constants for the reduction of europium in perchlorate and chloride media and the formal rate constants in sulphate, acetate and lactate solutions are reported. The rate increases in the order of increasing polarisability of the anion or the increasing stability of the complex,viz., perchlorate < sulphate > lactate ≈ acetate. The effect of methanol on the polarography of europium has been studied. In perchlorate and chloride media, the half-wave potential shifts to negative values and then to positive values as the methanol content is increased. In acetate solutions, the shift is continuously to negative potentials. This is attributed to the effect of complex formation in acetate media and ion-pairing in perchlorate and chloride media. The effect of viscosity on the diffusion current was found to obey the Stokes-Einstein equation.     

Complex compounds of thorium oxalate with ammonium oxalate

The system thorium oxalate-ammonium oxalate-water has been investigated by physico-chemical methods. A new procedure is adopted in preparing the solution for these studies by the mono-variation method. Data have been presented to prove the existence of two complexes in solution from measurements of electrical resistance, pH and relative viscosity.     

Polarography of potassium ethylxanthate,a titrant in amperometry

Polarograpbic studies of potassium ethylxanthate (RSH or xantbate) at the dropping mercury electrode (DME) reveal that the product of the anodic reaction is strongly adsorbed at the mercury drop as indicated by a prewave. The adsorbed film (0·15 mM to 1·0 mM xanthate solution) greatly affects the characteristics of the anodic wave of xanthate in aqueous medium. The current of main wave is proportional to the concentration of xanthate up to 2·5 mM in aqueous medium at DME. This electrode is used as an indicator electrode for amperometric titrations of metal ions with xanthate. Proper buffer composition and pH are developed for the accurate determination of metal ions. The combined use of the cathodic current of metal ions and the anodic current of xanthate under controlled pH conditions makes possible the amperometric titration of two metal ions in a mixture.     

Tensammetric studies of thiourea and its derivatives

Adsorption of thiourea and some of its derivatives at the mercurysolution interface has been studied by the tensammetric technique. It has been found that adsorption of thiourea increased the differential capacity rather than decreasing it. However the adsorption of S-methyl derivative of thiourea decreased the differential capacity. The N-substituted derivatives depressed the tensammetric curve of the supporting electrolyte to a greater extent than the N, N¹-substituted derivatives. The different behaviours of thiourea and its derivatives are discussed.     

Polarography of cobalt (II) in water and 50% methanol

The polarographic behaviour of cobalt (II) in water and 50% methanol in the presence of various supporting electrolytes has been studied. The kinetic parameters and activation energy for the electrode process have been evaluated and compared. The results have been discussed on the basis of selective hydration of cobaltous ion at the electrode surface.     

Emission spectrum of bismuth monochloride

Bismuth chloride has been excited in flowing condition with an uncondensed transformer discharge. About 390 bands are observed in the present experiments of which only 140 were recorded by earlier workers. The vibrational constants obtained are the same as those obtained by Morgan from obsorption experiments except for the addition of a cubic term for the upper state. It appears quite likely that the upper state of the system dissociates into Bi (⁴S_3/2) + Cl (²P_1/2) while the lower state, which is probably the ground state, dissociates into Bi (⁴S_3/2) + Cl (²P_3/2). The rough values of the dissociation energies obtained by extrapolations are D₀′=3750 cm.^?1 and D₀″=24614 cm.^?1     

Problems in nonhomogeneous media

Problems which can arise due to the variation in the properties of a medium are investigated by the use of alien transforms in conjunction with convolution. By way of illustration the method is applied to two particular problems.     

Resonances in periodic media

We study the propagation of linear acoustic waves (a) in an infinite string with a periodic material distribution, (b) in an infinite cylinder with a meterial distribution that is periodic in the longitudinal direction and does not depend on the transverse coordinates. We assume that the wave field is generated by a time-harmonic force distribution of frequency ω acting in a compact set. We show in both cases that resonances of order t^1/2 occur for a discrete set of frequencies and that the solution is bounded as t→∞ for the remaining frequencies. In case (a) ω is a resonance frequency if and only if ω² is a boundary point of one of the spectral bands of the corresponding spatial differential operator of Hill's type. A similar characterization of the resonance frequencies is given in case (b).     

Classical and quantum transport in random media

We study in this article the transport of particles in time-dependent random media, in the so-called weak coupling limit. We show the convergence of a Liouville equation to a Fokker–Planck equation. We also obtain the semi-classical limit of Schrödinger equations. This limit is described by a linear Boltzmann equation. In both cases, the ratio between a typical time scale and the scale of the media determines whether the limit diffusion and the collision process are elastic or not.     

Stability of reaction-fronts in porous media

The stability of reaction-fronts in porous media is studied with analytical and numerical methods. A stability criterion has been derived using linear stability analysis assuming a sharp font. The sharp front assumption is an approximation of the mathematical model in the limit of an infinite rapid reaction. The criterion shows that the stability of a sharp reaction front is dependent on the permeability that develops behind it. The sharp front is unstable for perturbations of any wave-length if the permeability increases behind the front. The criterion shows that short wave-length perturbations are more unstable than long wave-length perturbations. The sharp front is labile when the permeabilities are the same at both sides of the front. This means that the perturbed front moves unchanged forward. Finally, perturbations will die out in case the permeability decreases behind the sharp front. The stability of non-sharp fronts are simulated numerically when dissolution is by first order kinetics, the transport is by convection and diffusion and when the permeability and specific reactive surface depends on the porosity. The numerical experiments behave according to the stability criterion.     

Propagation and scattering of kinks in inhomogeneous nonlinear media

The model of kink scattering in inhomogenous nonlinear media is considered. The existence of kink bound states oscillating periodically and chaotically in time is shown. Translated from Teoreticheskaya i Mathematicheskaya Fizika, Vol. 112, No. 3, pp. 384–394, September, 1997.