ASTM D5558 Method for Determination of the Saponification Value of Fats and Oils
4. Procedure
4.1 Melt the sample, if not already liquid, and filter through filter paper to remove any impurities and the last traces of moisture. The sample must be completely dry.
4.2 Accurately weigh a sample, of such size (usually 4 to 5 g) that the back titration is 45 to 55 % of the blank, and 50 mL of the alcoholic KOH is added with a pipette, allowing the pipette to drain for a definite period of time.
4.2.1 Prepare a blank determination and conduct simultaneously with the sample.
4.3 Connect air condensers to the flask and boil the solution gently but steadily until the sample is completely saponified. This usually requires approximately 1 h for normal samples. Take care that the vapor ring in the condenser does not rise to the top of the condenser or there may be some loss.
NOTE 1 - Some samples particularly difficult to saponify may require more than 1 h. This can only be determined by trial. Clarity and homogeneity of the test solution are partial indicators of the complete saponification, but they are not necessarily absolute criteria.
4.4 After the flask and condenser have cooled somewhat, but not sufficiently to jell the contents, wash down the inside of the condenser with a little distilled water. Then disconnect the flask, add approximately 1 mL of indicator, and titrate the solution with 0.5 N HCl until the pink color has just disappeared.
