This discovery definitely marked a great step forward. However, since activity cannot be determined by actual direct measurement, it cannot be used as the basis for theoretical calculation of pH value. Accordingly, actual pH is determined by comparison with the pH of a specific solution, a standard solution that tends to maintain its pH value. Methods for measuring pH are defined by ISO and JIS.
When pH measurement became commonplace, differences between values measured for the same sample emerged as a problem. As a result, it became necessary to give a clear definition of pH and establish a method for selecting standard solutions. Hence, it became a pressing requirement that an effort be made to establish JIS regulations for pH measurement methods as soon as possible. Through various types of research and study, and with the cooperation of various types of organizations, JIS for pH measurement was established in March, 1957.
When drafting the JIS, the authors also referred to the standards for pH measurement in the United States, United Kingdom, and France. This is because the unit of pH is used internationally as well as in Japan. If individual countries created independent definitions, these would be unacceptable as international standards and would cause problems for academic and commercial activity.
For more detailed information on pH, please see the references below.
The following page gives an unmodified excerpt of part of “JIS Z 8802: Methods for determination of pH of aqueous solutions”. The JIS were established for industrial use. In order to gain a further, more precise understanding of pH, we recommend you to read - or reread - them through.
Kameyama: “Denki-kagaku no Riron oyobi Ouyou—Joukan I (Theory and Applications of Electrochemistry, First Volume I),” Maruzen Co., Ltd., 1963
Yoshimura, Matsushita, Morimoto: “pH no Riron to Sokutei-hou (Theory of pH and its Methods of Measurement),” Maruzen Co., Ltd., 1968
Kishimoto, Matsushita: “pH Sokutei to Jidouseigyo (pH Measurement and Automatic Control),” Nikkan Kogyo Shimbun, Ltd., 1968
Bates: “Determination of pH,” John Wiley & Sons, 1964
Ives, Janz: “Reference Electrodes,” Academic Press, 1961
“JIS Z 8802: Methods for determination of pH of aqueous solutions,” Japanese Standards Association
“JIS Z 8805: Glass electrodes for measurement of pH,” Japanese Standards Association
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