IP 136 Section 1: Petroleum products - Determination of saponification number - Part 1: Colour-indicator titration method

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  • Method adopted/last revised: 1998
  • Method reapproved: 2006
  • REF/ISBN: IP136S1-35231
  • Status: Current
  • First printed in STM books: January 1998


This part of IS0 6293 specifies a method for the determination, by colour-indicator titration, of the amount of constituents in petroleum products that will saponify under the conditions of the test. The method is applicable to materials having saponification numbers in the range 2 mg/g KOH to 200 mg/g KOH. Compounds of sulfur, phosphorus, halogens and some other compounds interfere by reacting with the alkali and acids under the test conditions.


1 The results on used crankcase and turbine oils, and on oils containing the interfering compounds above as additive constituents, should be interpreted with care, bearing in mind the possible higher values obtainable due to these additional reactants.

2 The interfering compounds above are contained in extraneous materials including certain organic acids and most nonalkali 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.

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