The melting point
(or, rarely, liquefaction point
) of a solid is the temperature at which it changes state
at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard
pressure. When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point
or crystallization point
. Because of the ability of some substances to supercool
, the freezing point is not considered as a characteristic property of a substance. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice", that is, the melting point.