1 This International Standard specifies a method for the determination of the existent gum in motor gasoline, aviation gasoline, volatile distillates used in their preparation and aircraft turbine fuel, at the time of test.
2 The determination of the unwashed gum content of motor gasoline is also specified.
3 The true significance of this method for determining gum in motor gasoline is not firmly established. It has been proven that high gum can cause deposits on induction manifolds, car-burettors and intake valves as well as sticking of intake valves, and in most instances it can be assumed that low gum will en-sure absence of induction-system difficulties. It should, however, be realized that the test is not of itself correlative to induction-system deposits. The primary purpose of the test, as applied to motor gasoline, is the measurement of the oxidation products formed in the sample prior to and under the condi-tions of the test, which are not as severe as those encountered in practical use. As many motor gasolines are purposely blen-ded with non-volatile oils or additives, the heptane extraction step is necessary to remove these from the evaporation residue so that the deleterious material, gum, may be determined.