ASTM D128 standard test methods for analysis of lubricating grease
FREE ALKALI AND FREE ACID
21. Free Alkali
21.1 Weigh a 10 to 30-g sample of the grease in a small beaker, dissolve as completely as possible in 75 mL of n-hexane by stirring with a spatula, wash the mixture into a 250-mL Erlenmeyer flask with a small amount of n-hexane, and rinse the beaker with 50 mL of 95 % alcohol (see 4.4), pouring the alcohol into the flask. Then add a few drops of phenolphthalein solution and shake the contents vigorously. If the alcoholic layer, after setting for a few seconds, is pink, add 10 mL of 0.5 N HCl, boil the solutions on a hot plate for 10 min to expel CO2, and titrate the excess acid back with 0.5 N alcoholic KOH solution. Calculate the free alkalinity in terms of hydroxide of the predominating base.
22. Insoluble Carbonates
22.1 If chalk or any other form of alkaline earth carbonate, or lead carbonate, is present as an insoluble, it will be detected by effervescence on adding the HCl. As the amount of such carbonates is likely to be considerable, increase the volume of 0.5 N HCl added sufficiently to dissolve all carbonate and leave a slight excess of acid. Boil the solution for 2 min, titrate the excess acid back with 0.5 N alcoholic KOH solution, and, from the acid consumed, calculate its equivalent in CaCO3, and so forth, disregarding any other forms of alkalinity that may have been present.
23. Free Acid
23.1 If the original alcoholic layer is not pink, titrate the unheated solution carefully with 0.5 N alcoholic KOH solution, shaking well after each addition. Calculate the acidity as oleic acid.
23.2 If soaps of iron, zinc, aluminum, or other weak bases are present, a determination of free acid is not possible since these metallic soaps react with KOH. Up to the present, no means has been devised whereby this determination can be made directly.
