Temperature and hysteresis errors in calomel half-cells

Abstract

Saturated and undersaturated KCI-calomel half-cells were subjected to temperature changes between 22.5 and 31.3° C and the difference in electromotive force (emf) between them and saturated calomel half-cells at 25° C was measured. During an 8° C change, maximum differences of 0.5 to 0.9 mv were found between the measured emf values and the equilibrium emf values corresponding to the temperature of the KCl solutions. Potentials within 0.2 to 0.3 mv of the equilibrium value were obtained in 2 to 3 hours after an 8° C change. Calomel half-cells protected with dewar flasks against small fluctuations in room temperature were more stable in potential than the unprotected cells. The saturated half-cell had a tlE/tlT of 0.25 mv/oC and the undersaturated h alf-cell, 3.8 N, gave the value 0.47 mv/o.C One half-cell, saturated at 25° C. without an excess of KCl crystals, was measured and its tlE/tlT was found to be erratic.

Definitions of pH Scales.

“…The potential of the saturated calomel electrode is not considered highly reproducible, and the use of this electrode as a standard cannot be recommended (113). Some possible causes of erratic behavior are hysteresis (163) and variations in the grain size of the calomel (162). Hence, one cannot expect always to make use of standard values of E0> + E¡ such as are given in the foregoing section.…”

Properties of Detergent Solutions

“…Calomel reference electrodes were maintained at the temperature of the solution under test, as were all the salt bridge connec- tions (Figure 1). When an electrode was taken to a higher temperature, it was first filled with a solution saturated with potassium chloride and calomel at a temperature higher than the working temperature and then maintained at the working temperature for several hours before use (30). Hydrogen electrodes were always employed in duplicate.…”

“…The saturated calomel electrode was found more convenient than the 0.10 N electrode and just as satisfactory, provided it was kept at constant temperature for several hours before use to minimize hysteresis (30). The Beckman saturated calomel electrode 1170 is designed to minimize hysteresis effects.…”

The Thermal Temperature Coefficient of the Calomel Electrode Potential between 0° and 70°C

“…The thermal temperature coefficient of the calomel electrode potential was originally studied by Gockel (1) and later in more detail by Richards (2). Subsequent investigations were conducted by Fales and Mudge (3), Ewing (4), Sorensen and Linderstrom-Lang (5), Kolthoff and Tekelenburg (6), Bjerrum and Unmack (7), Burian (8), Young (9), Wingfield and Acree (10), Cary and Baxter (11), and Ikeda and Kimura (12) (who investigated only differences between temperature coefficients in various aqueous chlorides). In most thermal emf studies, the temperature differential has been kept between 5 ~ and 10~ and the thermal temperature coefficient assumed to be valid at the median temperature, which was usually between 15 ~ and 25~…”