ABSTRACT
When a solid is placed in an atmosphere, it will adsorb (or absorb, depending on the substance) moisture from the atmosphere. The rate and extent to which this occurs is usually referred to as hygroscopicity. As well as a kinetic property it also contains a thermodynamic one, and definitions, such as those used for solubility (e.g., very slightly and slightly soluble) are not possible. At best one may talk about very hygroscopic substance (choline salts, for instance) and very nonhygroscopic substances (sand, for instance), but the large gamut of substances call for more detail to describe their hygroscopic classification.
