Sublimation

Not every substance passes neatly through solid-liquid-gas in sequence. Some substances change directly from the SOLID state to the VAPOUR state (and back) WITHOUT ever passing through an intermediate liquid state -- this is called sublimation, and such a substance is said to sublime. Dry ice (solid carbon dioxide) and iodine are familiar examples -- you can watch a piece of camphor or dry ice visibly shrink away as vapour without ever forming a puddle of liquid. During sublimation, the solid and vapour states of the substance coexist together in thermal equilibrium, just as s …