ASTM D94 Saponification Number of Petroleum Products
Saponification is the hydrolysis of fats or oils to form fatty acids and glycerol. The “saponification number” gives an indication of the amount of hydrolyzeable fat in a sample. Mineral oils normally have very low saponification numbers, animal or plant based oils normally have very high saponification numbers. This test determines the saponification number of lubricants, transmission fluids and additives.
The sample is combined with a standardized potassium hydroxide solution, refluxed, and titrated with hydrochloric acid. The endpoint is determined by either colorimetrically (method A) or potentiometrically (method B). The saponification number is reported in mg KOH per gram of sample.