Steam Distillation is a technique used for substances that are steam volatile and immiscible with water.

• Mechanism: The mixture (water + substance) boils when the sum of their individual vapor pressures ($P=P_{water}+P_{compound}$) equals the atmospheric pressure.
• Advantage: Since $P$ reaches atmospheric pressure before $P_{water}$ does (i.e., before $100^{\circ }C$), the substance distills at a temperature lower than its normal boiling point. This prevents the thermal decomposition of heat-sensitive compounds like Aniline or Essential oils.