Boiling Point (Boil•ing Point)

The temperature at which a liquid boils. Specific: the temperature at which the vapor pressure of a liquid is equal to the external pressure, the boiling point thus decreasing with a decrease in pressure (as 100 °C for water at a pressure of 760 mm of mercury and 51 °C at 100 mm)

Scum (Scum)

1. Extraneous matter or impurities which rise to, or are formed on the surface of liquids. 2. Any foul filmy covering floating on a liquid such as on a stagnant pool.