Phenomenological theory of the kinetics of ultrasonic emulsification

A working model is given for the rate of ultrasonic emulsification, considering the dispersion at the interface (area A) and the coagulations in the volume V of the emulsion. A bimolecular coagulation leads to the equation c=c∞tanh bt;c∞=(Aα/Vβ)1/2;b=(Aαβ/V)1/2 while a monomolecular coagulation gives c=c∞{1-exp (-at)};c∞=Aα/Vβ;a=β. The experiments on the dependence of c∞, a and b upon A and V favour the bimolecular coagulation. The results are satisfactorily explained on general theoretical grounds.

Raman spectra of crystalline double sulphates

Raman spectra of single crystals of K2M(SO4)2 · 6 H2O where M=Mg, Zn, Ni or Co have been recorded for the first time using λ 2537 as the exciting radiation. The corresponding five single sulphates have also been studied. Interesting results concerning the substitution of magnesium, zinc, nickel or cobalt in the double sulphate lattice on the sulphate frequencies are observed. The lattice spectra of these double sulphates are analysed group theoretically and discussed in relation to the lattice spectra of the corresponding individual sulphates. Certain new results concerning the Raman spectra of the individual sulphates have also been obtained and in the case of CoSO4 · 7 H2O the spectrum has been recorded for the first time.

Raman spectrum of strontium titanate

The Raman spectrum of strontium titanate has been recorded using λ 4358 of mercury as exciter. The observed spectrum consists of 7 Raman lines, one of which is of low frequency, as expected from the recent theory of Cochran. 6 of these Raman lines have been interpreted as the first order spectrum arising from a small deviation of the cubic strontium titanate from its idealized symmetry. It has been shown that one normal mode of SrTiO3 neglected by J.T. Last, will be really active in infrared absorption in the region of 440 cm-1 and that it has to be taken into account in the interpretation of the infrared spectra of titanates. The four vibrational modes of the unit cell of SrTiO3 correspond to frequencies of 90, 335, 441 and 620 cm-1 observed in Raman effect. The large width of the Raman lines and the additional lines at 256 cm-1 and 726 cm-1 have been attributed to a splitting of the longitudinal and transverse optical modes. With the observed frequencies it has been found possible to account for in a satisfactory manner the specific heat of SrTiO3 in the range 54·84° K to 1800° K.

The effect of temperature on the magnetic susceptibility of vanadium pentoxide systems

The magnetic susceptibilities of certain vanadium pentoxide systems supported by kieselgur have been determined in the temperature interval 30° to 400° C. The plot of reciprocal susceptibility against temperature for all the systems studied indicates sudden deflections at temperatures which are about 150° lower than those of optimum catalytic activity. It has been suggested that these points may mark the temperatures of commencement of structural changes which may be responsible for the activity of these catalysts.

Oxidation of polythionates with chloramine-T

Chloramine-T has been found to bring about the rupture of S-S link in polythionates in acid medium and oxidise all the sulphur present in the chain into sulphuric acid. Quantitative estimation of a polythionate may be made on the basis of this oxidation reaction.

Lattice vibrations and specific heat of zinc blende

The dispersion relations, frequency distribution function and specific heat of zinc blende have been calculated using Houston's method on (1) A short range force (S. R.) model of the type employed in diamond by Smith and (2) A long range model assuming an effective charge Ze on the ions. Since the elastic constant data on ZnS are not in agreement with one another the following values were used in these calculations: {Mathematical expression}. As compared to the results on the S. R. model, the Coulomb force causes 1. A splitting of the optical branches at (000) and a larger dispersion of these branches; 2. A rise in the acoustic frequency branches the effect being predominant in a transverse acoustic branch along [110]; 3. A bridging of the gap of forbidden frequencies in the S. R. model; 4. A reduction of the moments of the frequency distribution function and 5. A flattening of the Θ- T curve. By plotting (Θ/Θ0) vs. T., the experimental data of Martin and Clusius and Harteck are found to be in perfect coincidence with the curve for the short range model. The values of the elastic constants deduced from the ratio Θ0 (Theor)/Θ0 (Expt) agree with those of Prince and Wooster. This is surprising as several lines of evidence indicate that the bond in zinc blende is partly covalent and partly ionic. The conclusion is inescapable that the effective charge in ZnS is a function of the wave vector {Mathematical expression}.

Ultra-violet bands of mercury iodide

The ultraviolet bands of mercury iodide have been excited in uncondensed discharge and photographed with a quartz Littrow spectrograph. The bands in the region λ 2658 to 2530 Å have been analysed into two systems which may form the two components of a2Π-2∑ electronic transition with a2Π interval equal to 858·9 cm-1. These systems and the systems in the region λ 3095 to 2647 Å have the same lower state.

Phase change on transmission of microwaves through metal disc delay dielectrics

Expressions for the phase change Φ suffered by microwaves when transmitted through an artificial dielectric composed of metallic discs arranged in a three-dimensional array have been derived with different approaches as follows (i) molecular theory, (ii) electromagnetic theory and (iii) transmission line theory. The phase change depends on the distance t that the wave traverses inside the dielectric and also the spacing d between centre to centre of any two adjacent discs in the three principal directions. Molecular theory indicates Φ as an increasing function of t, whereas, the other two theories indicate Φ as an oscillatory function of t. The transmission line theory also exhibits Φ to be real or imaginary depending on t. Experimental values of Φ as a function of t have been obtained with the help of a microwave (3·2 cms wavelength) interferometer for two dielectrics having d as 1·91 cms and 2·22 cms respectively.

Polarisation studies on the Raman spectra of cubic crystals - Part I. Sodium chlorate

neral expressions have been derived for the intensities of the three classes of Raman lines namely totally symmetric A, doubly degenerate E and triply degenerate F, in the case of cubic crystals under the following conditions. The direction of the incident beam which is polarised with its electric vector inclined at an angle α to the normal to the scattering plane makes an angle Θ with one of the cubic axes of the crystal. The transversely scattered light is analysed by a double image prism with its principal axes inclined at angle β to the normal to the scattering plane, which is horizontal. For incident unpolarised light and Θ=22 1/2°, and the scattered light being analysed by a double image prism rotated through 45° from the position when its principal axes are vertical and horizontal ρ{variant} for A lines is equal to one, for E lines >1 and for F lines <1. This gives a method of classifying the Raman lines of a cubic crystal in a single setting. The results have been experimentally verified in sodium chlorate.

Energy dispersive backscattering of electrons from surface resonances of a disordered medium and 1/f noise

Anderson localised states in the bulk of a disordered medium appear as sharp resonances near the surface. The resonant backscattering leads to an energy-dependent random time delay for an incident electron. We derive an analytic expression for the delay-time probability distribution at a given energy. This is shown to give a 1/f noise for the surface currents in general.

An investigation of the PrBa2Cu3O7-δ system

Members of the PrBa2Cu3O7–delta system possessing the orthorhombic structure over a wide range of oxygen stoichiometry (delta=–0.5 to +0.5) have been prepared and characterized. Similar compositions with a tetragonal structure have also been prepared. None of the oxides is superconducting, independent of the structure or stoichiometry. Praseodymium seems to be present to a small extent in the 4+ state in oxygen-excess (negative delta) samples. Orthorhombic PrBa2Cu3O7–delta samples show the presence of twins suggesting that twins arise from orthorhombicity and have no relation to the superconductivity. A neutron diffraction study of a near-stoichiometric sample has shown a disordered orthorhombic structure with 72% occupancy of the 01 (chain) sites and with no interchange between Pr and Ba sites.