A method and apparatus are disclosed for sensing the changes in the electrical potential across a double layer. By using a conductive plug comprised of the same material that are in suspension in a fluid, the present method can be used to determine the timing and amount of agents to be added to the liquid to promote the removal of the particle. In one embodiment, the sensor is comprised of two closed chambers, a sensor chamber closed by a porous plug made from the subject material, and a reference chamber closed by a plug that prevents particle dispersion therethrough and also offers a negligible variation in double layer interface potential. An exemplary plug could be comprised of agar. Each chamber includes a corresponding electrode probe and is filled with a conductive solution.
To measure potential differences in second-class conductors without interference potentials, there are provided a potential generator cooperating with a potential-measuring structure. This structure includes a substrate of electrically highly insulating and chemically inert material embedding optical indicators whose optical properties change as a function of the applied electric potential difference. Both the potential generator and the potential-measuring structure have boundary surfaces which are in contact with the second-class conductor and opposite surfaces interconnected by an equalizing conductor. A light-measuring device is arranged for intercepting light changes in the indicators, thus measuring the potential difference.
