(Equivalent Test Methods: IP 136, ISO 6293, DIN 51559, JIS K 2503, and AFNOR T60-110)
EXPLANATION
Petroleum products may contain additives that react with alkali to form metal soaps. Certain used engine oils may also contain chemicals which will similarly react with alkali. The saponification number expresses the amount of base which will react with 1 g of the sample when heated in a specific manner. Since compounds of sulfur, phosphorus, halogens, and certain other elements, which are sometimes added to petroleum products also consume alkali and acids, the results obtained indicate the effect of these extraneous materials in addition to the saponifiable material present.
TEST SUMMARY
A known weight of the sample is dissolved in methyl-ethylketone or a mixture of suitable solvents. It is heated with a known amount of standard alcoholic potassium hydroxide for between 30 to 90 min at 80° C. At the end, the excess alkali is titrated with standard hydrochloric acid and the saponification number calculated. In Test Method ASTM D94, Method A - Color Indicator Titration, the titration is carried out manually with phenolpthalein indicator; in Test Method ASTM D94, Method B - Potentiometric Titration method, the titration is carried out potentiometrically.
TEST PRECISION
The precision of Method A procedure is given in figure below.
The precision of Method B, Potentiometric Procedure is:
Repeatability: 2.76 mg KOH/g
Reproducibility: 10.4 mg KOH/g
The bias of this test method is not known.