Crude oil is a mixture of many liquids. The crude oil enters the bottom of a tall column, where the mixture is heated. The substances rise up the column until they cool down and condense back to liquids.

The column separates the liquids by their boiling points. Substances with different boiling points condense at different heights as they cool, so the choice is boiling point. Density, magnetism, and physical state do not explain this separation process.

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