Anhydrisch

Anhydrisch is the German adjective describing a substance that lacks water. In chemistry, it is used for materials that have no water of hydration or no adsorbed moisture. The English equivalent is anhydrous. The term is commonly applied to reagents, solvents, and minerals that must be moisture-free to maintain stability or reactivity.

In chemistry, many compounds exist in hydrated forms, and the anhydrous form is often required for specific reactions or storage. Examples include copper(II) sulfate, which is blue as the pentahydrate CuSO4·5H2O but becomes CuSO4 when anhydrous, and sodium sulfate, which can be found as the decahydrate Na2SO4·10H2O in nature or solution but is used as the anhydrous salt Na2SO4 in many processes. Anhydrous salts are typically produced by dehydration methods such as heating, vacuum drying, or chemical drying with desiccants like phosphorus pentoxide.

Storage and handling of anhydrisch substances emphasize moisture control. Because many anhydrous reagents are hygroscopic or reactive with water, they are kept in dry environments, under inert atmosphere if necessary, and in containers with desiccants. Dry solvents and properly dried glassware are standard prerequisites in laboratories where moisture-sensitive chemistry is performed.

In mineralogy, anhydrisch refers to minerals without water of crystallization. A prominent example is anhydrite (CaSO4), which contrasts with gypsum (CaSO4·2H2O). The presence or absence of water in mineral structures often reflects the environmental conditions during formation and subsequent alteration.