Electronic Commutator Determination of E^o of Formation and Related Thermodynamic Quantities for Molten Lead Chloride¹

Emf of Isothermal and Nonisothermal Formation Cells of Molten Silver Halides

“…Pulsing current or the ratio of on-to offtime was increased until the extrapolated emf became constant with further increase in current. The vapor pressures of the silver halides (5,6) and the solubility of silver in silver chloride and silver bromide (7,3) are negligible in the temperature ranges of these measurements. In the absence of quantitative data concerning the solubility of silver in silver iodide and of each halogen in the corresponding silver halide, it has been assumed that these solubilities are negligible, and that the observed maximum extrapolated emf values at 1 atm are E ~ values.…”

“…Electrodes.--Each electrode consisted of a short length of spectroscopic graphite rod (Ultra Carbon Corporation, lot 1001-5, 3/32 in. diam) the pointed end of which had been thermally pretreated as described by Warner (2,3). The graphite was sealed in a 4-mm ID fused quartz tube by evacuating the tube and, hy heating, collapsing the quartz onto the graphite from 1 cm above the pointed end of the electrode for a length of 1-2 cm, which covered the junction of a platinum wire lead with the graphite.…”

“…Apparently this is due primarily to thermal gradients within the cells and/or to depolarization when the halogen is introduced too slowly or does not contact the entire surface of the electrode or, as in some cases, when its flow has been interrupted during emf measurements. The pulsed electrolysis, or electronic commutator, technique for determining the reversible E ~ of such cells has been shown to be reliable in studies with silver chloride (1) and lead chloride (2). In each case, however, a temperature existed above which it was not possible to produce cells free of depolarization, 910~ for AgC1 and 640~ for PbC12 (extended to 865~ with chlorine atmosphere above the melt).…”

“…Because no gas bubbles through the melt from an external source, it is easier to maintain a uniform cell temperature. A more detailed discussion of the technique has been given by Warner (3).…”

CHEMICAL EQUILIBRIA AT HIGH TEMPERATURES AND THE MECHANISM OF VAPORIZATION OF COMPOUNDS. Final Report.

“…The highest values of cell emf achieved were obtained during a run of short duration. After the first three measurements the cell resistance suddenly increased to 240 ohms after having been 21,18 The above difficulties were not encountered in the work with the other halides.…”