This part of IEC 62021 describes a procedure for determination of the acidity of unused and used electrical mineral insulating oils.NOTE 1: In unused and used mineral insulating oils, the constituents that may be considered to have acidic characteristics include organic acids, phenolic compounds, some oxidation products, resins, organometallic salts and additives.The method may be used to indicate relative changes that occur in a mineral insulating oil during use under oxidizing conditions that may or may not be shown by other properties of the resulting mineral oil.The acidity can be used in the quality control of unused mineral oil.As a variety of oxidati