• Method adopted/last revised: 1994
• Method reapproved: 2004
• REF/ISBN: IP001-2934869
• Status: Current
• First printed in STM books: January 1994

Scope

This standard describes methods for the determination of the acidity of unused lubricating oil (see note 3), fuel oil, and petrolatum.

Two alternative methods, A and B, are given for the determination of acidity. Method A is more suitable than method B for dark coloured oils and oils of viscosity higher than 120 mm2/s (cSt) at 40 C and petrolatums. Method B is often preferred for pale coloured, low viscosity oils such as transformer oil. Method C is used to calculate organic acidity.

Note 1 Oils containing additives may give erroneous results.

Note 2 If there is elemental sulfur in solution, method A shold be used, as method B may give rise to erroneous results due to interference with the indicator.

Note 3 The acidity of oxidized oils may also be determined by this method but precision has yet to be established.

Note 4 Results obtained by IP 139 are generally comparable with those obtained by method A of this standard, though with some oils, particularly used oil and those containing additives, there is a tendency for higher figures to be obtained.