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API scale (American Petroleum Institute scale):
- Definition: The API scale, developed by the American Petroleum Institute (API), is a measure of the relative density or specific gravity of petroleum liquids compared to water. It is calculated using the formula:
\[
\text{API Gravity} = \left( \frac{141.5}{s} \right) – 131.5
\]
where ( s ) is the specific gravity of the petroleum liquid relative to water at 15.56°C (60°F). - Usage: The API Gravity scale is widely used in the petroleum industry to classify crude oil and other liquid hydrocarbons based on their density characteristics. Higher API Gravity values indicate lighter oils (less dense), while lower values indicate heavier oils (more dense). This classification is important for determining the quality and refining properties of crude oil.