Vapor pressure: the pressure of a pure liquid in equilibrium with its vapor.  A sealed container partially filled with liquid and evacuated will reach equilibrium. Vapor pressure increases with increasing temperature.  The equilibrium can be represented by the general equation:

liquid gas

For example, for water the equation would be:

H₂O (l) H₂O (g)

Vitamin C: unlike most mammals, humans cannot manufacture vitamin C (ascorbic acid), so it must be provided by our diet.  Ascorbic acid is required by the body for the formation and maintenance of collagen, the primary substance of skin, blood vessels, and the connective tissues which hold our bodies together.  Vitamin C works as a coenzyme to convert proline and lysine (amino acids) to hydroxyproline and hydroxylysine, which are both important to the collagen structure.  Without enough vitamin C, the connective tissue begins to break down, in the disease called scurvy.  Early symptoms of scurvy are bleeding gums and sore teeth.  Scurvy is an exceptionally rare disease today, since we have plenty of fresh fruits and vegetables in our diet.  Nobel Prize winning chemist, Linus Pauling, advocated taking large doses of vitamin C as a cure for the common cold.  However, there is no statistical evidence that it does so, though it may relieve some cold symptoms.  Other suggested benefits of vitamin C are as a cancer-preventing agent, since it is an anti-oxidant and free-radical scavenger.  This is highly speculative.  There is no substantiated evidence of any benefit to humans from vitamin C in doses above those required to prevent scurvy.