calomel electrode
A reference electrode used in electrochemistry, consisting of mercury and mercury(I) chloride (calomel) in contact with a potassium chloride solution.
In pH measurement, a calomel electrode is often used as the reference electrode.
From English 'calomel' (mercury(I) chloride) + 電極 (electrode). The term 'calomel' originates from Greek 'kalos' (beautiful) and 'melas' (black), referring to its color change upon reaction.