The measurement of conductivity in electrolytic solutions

A simple conductivity cell is shown in Fig. 31.2. Two platinum electrodes are sealed in the ends of the cell. These are usually coated with a deposit of finely divided platinum, platinum black, to eliminate some of the effects of electrolysis. The cell is filled with the solution, and the resistance is measured by placing the cell in one arm of the alternating current version of a Wheatstone bridge. The frequency ordinarily used is about 1000 Hz. 

The cell constant K = l/A depends on the geometry of the cell it can be determined for cells of special design by measuring the distance I between the electrodes and the area A of the electrodes. In routine measurements the cell constant is determined indirectly by measuring the resistance of the cell containing a standard solution of known conductivity. Solutions of potassium chloride are commonly used for this purpose. Some values of k for KCl solutions are given in Table 31.3. 

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