The new immersion type calomel reference electrode was designed for the pH measurement at the high pressure. The electrode is for preventing the error apt to occur when the pressures are not equal at the both sides of the junction between the inner solution and test solution, and can use the pressure up to 13kg/cm2. The pH measurement was carried out at 60°C and 10kg/cm2, using the new type calomel reference electrode and the commercial glass electrode. In the measurement of pH 4.01 buffer solution in the nitrogen atmosphere at 10kg/cm2, the change of pH value was not recognized. In the measurement of the pH value under the vinyl chloride polymerization reaction at the high pressure, however, it was found that the pH value deviated from 5.2 to 3.5.
