desiccant

n.
A substance, such as calcium oxide or silica gel, that has a high affinity for water and is used as a drying agent.

[From Latin dēsiccāns, dēsiccant-, present participle of dēsiccāre, to desiccate. See desiccate.]

desiccant des'ic·cant adj.

A substance (adsorbant) used to withdraw moisture from other materials. Although the removal of large quantities of water is done by evaporation, aided by moving air currents and by elevated temperature, the last traces of moisture are often held very tightly and do not evaporate readily. Furthermore, evaporation ceases when the moisture content of the material is reduced to that of the drying-air current. For final drying, a desiccant is used. It may react with water chemically or retain water through capillarity of adsorption. The drying agent is placed directly into the gas or liquid to be dried; solid materials are placed in a desiccator, a closed vessel in which moisture diffuses to the desiccant through the dry desiccator atmosphere. A desiccant loses potency as it takes on water; often it can be renewed by heating. Desiccants which form hydrates can be selected to maintain certain levels of low humidity in a closed vessel. See also Adsorption; Deliquescence.

Among the more important types of solid desiccants are silica gel, activated alumina, anhydrous calcium sulfate, magnesium perchlorate, oxides (of barium and calcium), and activated carbon.

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Any absorbent or adsorbent, liquid or solid, that will remove water or water vapor from a material. In a refrigeration circuit, the desiccant should be insoluble in the refrigerant.

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1. promoting dryness.
2. an agent that promotes dryness.