A laboratory desiccator is a pot that is used to absorb water vapors from chemical reagents that are hygroscopic, which are reagents that absorb water. This allows for the accurate measurement of the chemicals before any reaction occurs and ensures that the appropriate amount of reagents are used.
The most common desiccators used in labs are circular and made of heavy glass. These desiccators have two compartments: a lower compartment that stores a desiccant and an upper compartment where the reagent is placed. Desiccants are drying agents that are used to ensure that any water vapor still present is absorbed before reaching the reagents. These desiccants are typically made of sodium chloride or silica gel. The reagents inside the desiccator are exposed to water vapor whenever the desiccator is opened and require some time before low humidity levels are achieved. Because of this, desiccators aren't used in situations in which the reagent reacts quickly or violently with water, such as what occurs with alkali metals like sodium.
Dessicators are typically sealed off from outside air, and some models include a vacuum fitting for further evacuation of air. Samples that are almost dry are typically placed in desiccators to remove any remaining water vapor. If further drying is required, the samples are dried at elevated temperatures using a drying pistol.