On the action exerted by antagonistic electrolytes on the electrical resistance and permeability of emulsion membranes

Abstract

Artificial emulsion membranes suitable for electrical conductivity and permeability experiments may be prepared by interposing layers of filter paper saturated with an emulsion of oil in soap between supporting sections of rubber tubing in a glass U-tube of the type commonly employed for electrical conductivity determinations. A thicker layer or film of emulsion is generally preferable and may be prepared by introducing into the U-tube a section of rubber tubing of any desired length which is then filled with emulsion. Retaining layers of filter paper above and below are held in position by additional supporting sections of tightly fitting rubber tubing. Emulsion membranes of this type when exposed to the influence of various antagonistic electrolytes exhibit variations in electrical conductivity and permeability corresponding almost exactly with those observed by Osterhout in the case of laminaria under similar working conditions. For example, .52 M NaCl causes a rapid rise in the conductivity of a saturated filter-paper membrane until the level of the environing solution is almost reached, while .278 M CaCl2 causes first a considerable fall in conductivity which is followed subsequently by a rise to approximately the same level as in the case of NaCl. The most remarkable paralleling of Osterhout's results may be obtained by exposing emulsion layers or films to brief alternating treatments with NaCl and CaC12. As in the case of laminaria, alternating variations in conductivity within comparatively wide limits may be obtained without any apparent injury to the membrane which may subsequently be returned to sea-water or a balanced solution of NaCl and CaCI2 and exposed to a similar treatment the next day. However, just as in the case of laminaria, too prolonged an exposure to either NaCl or CaCl2 may cause changes in electrical conductivity and permeability beyond the critical point at which recovery is still possible and the membranes subsequently exhibit extremely erratic results or fail entirely to respond to treatment.