ABSTRACT
Some substances lose their hydration waters on exposure to air, these are termed efflorescent; others gain water and are said to be hygroscopic. A hydrate of importance in the medical field is Plaster of Paris;
(CaSO4)2 · 2H2O + 3H2O 2(CaSO4 · 2H2O) Plaster of Paris (soft) Gypsum (hard)
Another hydrate, MgSO 4 · 7H
Epsom salts.
