Effect of the solubility of glass on the behavior of the glass electrode

Application of an interferometer method previously used for determining the relative solubility of optical glasses, to a glass which is commonly used for making glass electrodes, gave results leading to the following conclusions:1.The solubility increases rapidly as the pH of most solutions increases above 8.5 or 9.2. At all values below pH 7 for the solutions investigated (except 10 N H 2SO,) this glass exhibits a slight swelling.3. The rate of swelling is repressed in the acid region beyond pH 2. 4. At intermediate pH values 3.1 to 4.0 the rate of swelling is repressed by high concentrations of magnesium suUate.Considering these conclusions in connection with the performance of glass electrodes, these regions of marked solubility change correspond to the regions of pronounced voltage departures exhibited by electrodes made from this glass.That the anomalies of the glass electrode are definitely associated with the solubility of the glass has been further demonstrated both by the use of glasses which do not exhibit swelling in the acid range, (and hence no detectable change of swelling in the "super-acid region"), and by measurements made in alkaline solutions, such as aqueous ammonia, in which soluble silicates are not formed.Under these circumstances the voltage departures are greatly decreased or completely eliminated.For every case investigated, voltage departures of the glass electrode have been found to be accompanied by changes in the solubility of the glass.