scope:

This standard specifies a method of determining the saponification number of the mineral oils specified in Clause 1. The saponification number serves to determine the content of saponifiable constituents of mineral oils. The method specified allows relative changes to be detected which occur in a mineral oil during operation due to a change in the saponification number.

This standard applies to new and used mineral oils, including those containing additives (e.g. of animal and plant origin), which are saponifiable under the conditions specified in this standard. It should be noted that alkali or acid consuming compounds of sulfur, phosphorus, halogens or other elements are likely to affect the result. This aspect shall be taken into account when interpreting results obtained from such products. In such case the saponification number is suitable only for identifying the change in the oil.

NOTE The substances referred to above, which are not considered saponifiable, include inorganic or organic acids, and most nonalkali soaps. The presence of such substances increases the saponification number above that of fatty saponifiable matter. The odour of hydrogen sulfide near the end of the back titration is an indication that certain reactive sulfur compounds are present in the sample. Other reactive sulfur, chlorine, and phosphor compounds give no simple indication during the determination of the actual fatty acid content. A gravimetric determination of the actual fatty acid content is probably the most reliable method for determining such compounds. ASTM D 128:1998 can be used to determine fatty acids gravimetrically.