7. Procedure
7.1 Weigh, to 0.1 mg into a 250-mL Erlenmeyer flask, the correct amount of sample for acetylation determined as follows:
7.2 Weigh 9.0 to 11.0 g of the sample into another flask for the acid value. If the test method is being used for fatty acids, such as hydroxystearic acid, the weight should be 0.9 to 1.1 g.
7.3 Pipet 5.0 mL of the pyridine-acetic anhydride solution into the flask containing the specimen for acetylation. For samples having 0 to 20 hydroxyl value, add an additional 5 mL of pyridine to the flask. Thoroughly mix the contents by gentle swirling. Pipet another 5.0 mL of pyridine-acetic anhydride solution into an empty flask for the reagent. Add 10 mL of pyridine, neutralized to phenolphthalein, to the specimen for the acid value blank. Thoroughly mix the contents by gentle swirling.
7.4 Insert reflux condensers into the Erlenmeyer flasks. Place the flasks on an opening of a steam bath and heat for 1 h. By this method of heating only slight, if any, refluxing will occur.
7.5 Add 10 mL of water through the condensers to the flasks. Heat on the steam bath for an additional 10 min with reflux condensers attached. Allow the flasks to cool to room temperature with condensers still attached.
7.6 Add 25 mL of neutralized n-butyl alcohol to each flask in the following manner. About half should be added through the condenser, the condenser removed, and the remaining alcohol used to wash down the sides of the flasks. Add 1 mL of phenolphthalein indicator solution to each flask and titrate to a faint pink end point with 0.5 N alcoholic KOH solution.