The milligrams of KOH required saponifying 1 g of oil known as saponification value determination of saponification value accurately weighed quantity of oil is taken in a flask and 50 mL of 0.1 alcoholic KOH is added. The mixture is heated over water bath using water condenser for one hour. The contents are cooled and amount of unreacted KOH in the flask is estimated by back titration with × N HCl using phenolphthalein indicator.
Similarly, a back titration without oil sample is carried out
The saponification value calculated by-
Saponification value of oil = (volume of ×NHCl-volume of ×NHCl@in blank titration (mL-in back titration (mL))/(weight of oil taken (g))
Significance of saponification value
Petroleum oils do not saponify whereas vegetable and animals oils have a characteristic saponification value. Saponification value indicates presences of vegetable and animal’s oils additive in blended lubricating oils Each blended oil has its own characteristics saponification value hence any deviation indicates changes of adulteration.