Superheatedand supercooled liquids exist in a state of precarious equilibrium knownas metastable equilibrium.
Metastable liquids can also exist under tension,that is to say, at negative pressures.
In trees, mineral nutrients and water for photosynthetic transpirationare conveyed upwards from roots to leaves as liquid columns under tension. Metastable liquids can also be found in mineral inclusions and clouds. Novel cryopreservation technologies rely on the deep supercooling of aqueoussolutions to increase the shelf life of labile biochemicals. These andother examples attest to the natural and technological importance of metastableliquids. Fundamental questions on the physics of fluids arise in connectionwith metastability.