Observation of the “geoelectric effect” in electrochemical concentration cells using ion-exchange membranes

Abstract

1. The potential of the cell, Ag, AgCl, 0.001 M NaCl, cationic ion-exchange membrane, 0.1 M NaCl, Ag, AgCl, exhibits a decrease of 30 mv when the plance of the membrane is changed from vertical to horizontal with the 0.001 M NaCl solution on top. Upon returning the membrane plane to the vertical position, the cell potential recovers to a value at least as large as that expected for the undisturbed cell after passage of a time period of similar magnitude. 2. The potential of the cell, Ag, AgCl, 0.001 M NaCl, anionic ion-exchange membrane, 0.1 M NaCl, Ag, AgCl, exhibits an increase of 20 mv when the plane of the membrane is changed from vertical to horizontal with the 0.001 M NaCl solution on top. This change in potential also appears to be reversible upon returning the membrane plane to the vertical position. 3. These membrane concentration cells show similar behavior when the acceleration force is applied by means of a centrifuge. The maximum GEE resulted when the tangential component of centrifugal acceleration cancelled the tangential component of gravitational acceleration; that is, when the net tangential component of acceleration on the membrane was zero. 4. In an effort to ascertain if the GEE is due to simple osmotic-density gradient phenomena, the GEE was determined for cells containing the usual cationic ionexchange membrane and sodium chloride-water-ethanol solutions which produced known osmotic flow rates. The GEE was observed under conditions of zero osmotic transfer of liquid. 5. The GEE results from the formation of a stagnant region or layer of more concentrated more dense solution resting upon the upper surface of a horizontal membrane. 6. The GEE is not observed when the cell solutions are stirred mechanically; the cell potential is completely indifferent to orientation in the gravitational field.