Liquid measure - Wood, Glass - 1920-1930

A pH meter is a scientific instrument that measures the activity of hydrogen ions in aqueous solutions, indicating their acidity or basicity expressed in pH. [ 2 ] The pH meter measures the electric potential difference between a pH electrode and a reference electrode; it is therefore sometimes called the potentiometric pH meter. This electric potential difference is related to the acidity, or pH, of the solution. [ 3 ] The measurement of pH using a pH meter (pH-metry) is used in many applications, ranging from laboratory experiments to quality control. [ 4 ]