Boil

Boiling is the rapid transformation of a liquid into a vapor caused by the formation of vapor bubbles within the liquid. This occurs when the liquid’s vapor pressure equals the surrounding pressure, a condition defined by the boiling point. At sea level, pure water boils at 100 degrees Celsius (212 degrees Fahrenheit); impurities, pressure, and heat transfer conditions can raise or lower the effective boiling temperature. Lower ambient pressure lowers the boiling point, which is why water boils at lower temperatures in high-altitude environments.

Boiling involves several mechanisms. Subcooled liquids are heated toward the boiling point, at which nucleation sites in the liquid encourage bubble formation. Nucleate boiling features bubbles that rise and release heat to the surrounding liquid. If heat input is high and the liquid film around a surface becomes insulating, film boiling can occur, reducing heat transfer. In practice, boiling can be categorized as vigorous rolling boiling, simmering, or occasional bubble formation, depending on temperature, pressure, and agitation.

Applications of boiling include cooking, sterilization, and industrial heat transfer. In power generation and chemical processing, controlled boiling is used in boilers and distillation columns to separate mixtures or transfer energy efficiently.

Boil can also refer to a skin infection, a furuncle, caused by bacteria such as Staphylococcus aureus. A boil appears as a painful lump, often with redness and swelling. Treatment typically involves warm compresses and, in some cases, antibiotics or drainage by a healthcare professional. Good hygiene reduces risk, and seek medical care for expanding redness, fever, or signs of infection spreading.

Other related terms include evaporation, heat transfer, and phase transition.