| the portion of a hydrate that is represented as, or can be expelled as, water: now usually regarded as being in true molecular combination with the other atoms of the compound, and not existing in the compound as water. |

| water of hydration n. Water chemically combined with a substance in such a way that it can be removed, as by heating, without substantially changing the chemical composition of the substance. |
water of hydration n.
Water chemically combined with a substance in such a way that it can be removed, as by heating, without substantially changing the chemical composition of the substance.
| water of hydration
Water that is chemically combined with other molecules to form a hydrate mineral and that is easily removed through heating. |