- Method ASTM D381
- Repeatability variable, see method
- Reproducibility variable, see method
- Blending non-linear
- Additive Correction No
The purpose of this test is to identify if there are compounds that will oxidize quickly under heat and air jet evaporation. When the compounds combine and form longer insoluble oxidized chains they are called gums. There is however an issue with this test. If the product contains other contaminates that are heavier than gasoline (vgo, fuel oil, etc) they will not evaporate and will stay in a liquid form. This causes issues with the test results during the heptane wash. The heptane will mix with the liquid residue and wash out even though there is heavier product that will not wash out during combustion. As a result both washed and unwashed gums should always be asked for when purchasing products to ensure there will be no issues later on.
The test is performed by adding 50mls of sample to a weighted beaker. This is then placed in the heating bath and injected with air for gas and steam for jet. Once 30 minutes passes it is pulled and cooled in order to get the unwashed result. The sample is then washed with heptane and decanted off. Then it is placed back into the bath to evaporate the heptane. After it is pulled and cooled to perform the final weight for the washed gum result. The result is expressed as milligrams per 100ml of sample.