Allen B. Scott

The Magnetic Susceptibility of Potassium Ferrate

A method of preparation of potassium ferrate of 97 percent purity is described. Although the product contained an inseparable ferromagnetic impurity, the susceptibility of the ferrate was determined by extrapolation to infinite field strength of data obtained by the Gouy method. The observed effective magnetic moment of the ferrate ion agrees approximately with that expected for hexavalent iron.

Transference Experiments on Lead and Thallous Ions in Potassium Chloride Crystals

The electrolytic migration of lead and thallium in potassium chloride crystals to which small additions of lead chloride and thallous chloride have been made has been studied in a transference experiment. Lead was found to migrate toward the anode, indicating that it is bound in a negatively charged complex. Thallium did not migrate appreciably at temperatures below 600°; at higher temperatures it moved toward the cathode. Thallium clearly may exist as the simple cation at elevated temperatures; however, the results at lower temperatures do not permit a conclusion to be drawn with certainty regarding the existence of complex ions.

Chemical Determination of the Oscillator Strength of F Centers

The concentration of F centers in additively colored KCl was determined by measuring the amount of hydrogen evolved when the colored crystal is dissolved in water. This method avoids the uncertainties inherent in previous experiments on the change in acidity occurring upon dissolution. The use of this concentration in the Smakula absorption equation gives the optical oscillator strength f. The value of f, based upon 12 independent experiments, was 1.17±0.15, which disagrees with previously reported values.

Absorption Spectra of Luminescent Thallous Chloride Solutions

The absorption spectra of solutions of KCl, made luminescent by the addition of TlCl, have been analyzed with the assistance of dissociation constants for TlCl and TlCl2— obtained from solubility measurements. Absorptivities for each of the absorbing species have been found at several wavelengths. Spectra of solutions having a wide variety of KCl and TlCl concentrations were calculated from the absorptivities and dissociation constants; these agree quite well with the observed spectra except at high Cl— concentration, where the disagreement is ascribed to the formation of more highly coordinated complexes. Decrease of dielectric constant of the solvent shifts the absorption band in the direction to be expected from an increase in the stability of molecular TlCl and the complex ions.

Discharge Mechanism of the V 2 O 5 Electrode

Abstract : The behavior of V2O5 single crystals, grown from the melt, during cathodic polarization and recovery, was investigated. The dependence of potential upon pH showed that the only plausible reduction product was a solid oxide or oxyhydroxide, polarization being due to the formation of a solid solution. In the pH range 2.0 - 5.5, the curve of electrode potential vs. time during both polarization and recovery was accurately predicted by an equation, already applied to MnO2, derived from the assumption that the product is removed from the surface by diffusion into the electrode. Using tritium as a tracer, it was shown that hydrogen is incorporated in the electrode during discharge at pH 4.7. The activation energy for diffusion was found to be 6.7 kcal/mole, which is consistent with bipolar diffusion of protons and electrons. (Author)

Electron Traps in Deformed Alkali Halide Crystals

Additively colored KBr and KCl crystals were deformed at room temperature, illuminated with F light at −140° and −120°C, respectively, to produce F′ centers and then warmed from −186°C to room temperature. Absorption spectra were obtained at a series of temperatures during warming. Curves of absorption in the region of the F′ band vs temperature showed two temperature regions in which the absorbance decreased rapidly, corresponding to the decomposition of two sets of centers of differing thermal stability. Undeformed crystals displayed only one such temperature region, in which ordinary F′ centers were destroyed. The centers in deformed crystals may be F′ centers whose stability is either increased or decreased by the influence of neighboring dislocations. In deformed KCl a new center, absorbing near 1500 mμ and more stable thermally than F′ centers, was found.

Z‐Center Energy Levels

One of the centers proposed to account for Z‐band absorption in alkali halide crystals consists of an electron trapped at the divalent cation. A calculation of the absorption energy has been made using the method of Simpson. This method, though not free of objections, has been surprisingly successful in predicting F‐band absorption maxima.For Ca++ in KCl and NaCl, the absorption maxima were found to lie at 3.92 and 3.70 eV, respectively, for Sr++ at 9.00 and 8.70 eV. These locations are far removed from the Z bands, which lie near 2.0 eV in both crystals. While the numerical accuracy of the calculations is not high, the possibility of a Z‐type center absorbing in the far ultraviolet is raised; this has a bearing on recent thermodynamic arguments concerning the nature of Z centers.

Motion of F Centers in KCl and KI

The drift velocity of F centers in KCl and KI as a function of temperature is determined. The electric field producing this motion in the colored portion of the crystal is measured directly. The electric field in the uncolored region is found to be appreciably higher than the field in the colored portion.The thermal ionization energy for F centers is found to be 2.4 eV for KCl and about 2.0 eV for KI.

Thermodynamic Properties of Molten Mixtures of Cobalt Chloride with Some Alkali Halides

Thermodynamic properties including the activity coefficient, and the partial molar free energy, enthalpy, and entropy of mixing have been determined for the solute in the solvents , , , and . Values of the properties were established by measuring the reversible emf of cells of the type where represents an alkali metal cation. Cell emfs were determined over a range of concentration from approximately 10−4 to as high as fraction of solute and temperatures ranging from the melting points of the solvents to 900° C. Experimentally determined values of the quantity , the standard change in Gibbs function for the reaction have been found to agree to within 1 kcal with values calculated on the basis of Brewers (19) tabulation: the agreement with values calculated fromother data in the literature is not as close, but is still within the stated limits of uncertainty of the data. Reference electrodes of the type which utilized solid porcelain as a bridge, were immersed in the same melts and allowed continuous monitoring of chlorine electrode potentials as solute concentrations varied.

New electron-excess color centers in KCl: Effect of O2− and SO2−4 ions☆

Abstract Two new absorption bands, along with the T bands previously reported by Ring and Grossweiner, have been observed in additively colored KCl. The bands are developed by bleaching F centers at high temperature in relatively pure KCl, but may be produced rapidly at room temperature in colored KCl crystals containing O 2− , or in sulfate-doped KCl which has been additively colored. It is proposed that the development of these bands is accelerated by the presence of negative ion vacancies introduced as charge compensation for the divalent anions, and that the new centers are aggregates containing one or more F centers with a vacancy pair. The segregation coefficient of K 2 SO 4 in KCl, between crystal and melt, was found to be 1.0 × 10 −3 .