Ash determination in mineral oils is an analysis method used to determine the amount of inorganic material remaining as a result of oil combustion. This inorganic material is caused by the additives contained in the oil, especially the detergent and dispersant additives. It gives information about the amount of ash, the formulation of the oil and the amount of additives used.

**ASTM D874:** This standard includes the procedure for determining the sulfate ash content of mineral oils.

**Test Administration:**

1. **Sample Preparation:** A specified amount of oil is weighed in a porcelain bowl.

2. **Combustion:** The oil is burned at a specified temperature. This causes the organic components in the oil to burn off, leaving only the inorganic components (usually in the form of sulfates).

3. **Ashing:** The residues left after combustion are baked at a higher temperature for a certain period of time, and ashing is carried out. This process ensures complete combustion of all organic material.

4. **Cooling and Weighing:** After ashing, the ash is cooled and weighed. This weight indicates the ash content of the oil.

5. **Calculation:** Ash content is expressed as a percentage of the weight of the original oil sample.

This test gives information about the additives used in the formulation of the oil. A high ash content may indicate a high detergent and/or dispersant additive content. However, this is not always a positive thing. For example, high ash content in diesel engine oils can cause particulate filters to clog, so a low ash content is preferred in some modern diesel engine oils.