This part of ISO 6293 specifies a method for the determination, by potentiometric titration, of the amount of constituents in petroleum products that will saponify under the conditions of the test. ISO 6293-1 specifies a determination by colour indicator titration. The method is applicable to materials having saponification numbers in the range 2 mg KOH/g to 200 mg KOH/g. Compounds of sulfur, phosphorus, halogens and some other compounds react with the alkali and acids under the test conditions. NOTES 1 The results on used crankcase and turbine oils, and on oils containing the compounds above as additive constituents, should be interpreted with care, bearing in mind the possible higher values obtainable due to these additional reactions. 2 These extraneous materials include certain organic acids and most non-alkali soaps. The odour of hydrogen sulfide near the end of the back-titration step is an indication of the presence of certain reactive sulfur compounds, but other reactive sulfur compounds, as well as those of chlorine, phosphorus and other interfering materials, give no simple indication during the test. A gravimetric determination of fatty acid content is an alternative procedure for the estimation of such compounds.