boiling point

Boiling point is the exact temperature at which a liquid turns into vapour throughout its entire volume, not just at the surface.

• It isn't fixed for all conditions — a liquid's boiling point drops at lower atmospheric pressure, which is why water boils below 100°C on a high mountain and cooks food more slowly there.
• A pressure cooker works on the opposite trick: trapping steam raises the pressure inside, pushing water's boiling point above 100°C so food cooks faster.
• Unlike evaporation, which happens quietly and only at the surface, boiling is fast and visible — bubbles of vapour form deep inside the liquid and rise up.

Every pure liquid has its own characteristic boiling point, which is one reason it's used to identify or separate substances, like in distillation.