Hydrate

Hydrate, any of various chemical compounds composed of water and some other substance. Common hydrates include blue vitriol (CuSO₄5H₂O) and Glauber's salt (Na₂CO₃10H₂O). As water evaporates, most hydrates change structure. Water that is retained by the hydrate is known as water of crystallization or hydration. Hydrates that have lost all water are called anhydrous.