nonhydrous

Nonhydrous refers to substances that do not contain water, either in the form of water of crystallization, adsorbed moisture, or structural hydroxyl groups. The term is often used interchangeably with anhydrous in many contexts, though some sources reserve anhydrous for substances that have no water of crystallization, while nonhydrous can also imply the absence of any water of hydration or moisture. In chemistry, nonhydrous materials are essential when moisture interferes with reactions or storage; for example, Grignard reagents and many organometallics are extremely reactive with water, so they are prepared and kept in dry, inert environments. Drying methods include heating to drive off water, chemical drying agents (calcium hydride, anhydrous calcium chloride), adsorption drying with molecular sieves, and distillation over drying reagents under inert gas.

In mineralogy and geology, nonhydrous or anhydrous minerals lack water in their crystal structure, whereas hydrous minerals contain hydroxyl groups or water within their lattice. This difference affects density, stability, and metamorphic behavior. In materials science and pharmaceuticals, the presence of water can alter solubility, stability, and shelf life, so nonhydrous forms are often favored for processing or storage.

Measurement and verification of nonhydrous status rely on techniques such as loss on drying and Karl Fischer titration to quantify water content. Overall, nonhydrous materials are defined by the absence of water in any form and are contrasted with hydrous or hydrated variants across scientific disciplines.