the ph of a chemical copper plating solution is exactly measured for a prolonged time by utilizing a copper oxide prepared by etching metallic copper in an 0 . 1 - 1 n inorganic acid then oxidizing the etched metallic copper in an aqueous 0 . 1 - 1 n alkali metal hydroxide solution as a main electrode for ph measurement or reducing agent concentration measurement in terms of ph . a combination of the ph measurement with well known procedures for measuring concentrations of cupric ions and a complexing agent exactly measures the ph and the concentrations of a reducing agent , cupric ions and a complexing agent for a continuation of longer time than the conventional procedures .