A desiccator is a specialized piece of laboratory equipment designed as a controlled, sealed storage container. Its primary purpose is to create and maintain an atmosphere with extremely low humidity, protecting sensitive contents from ambient moisture. This apparatus is foundational in chemistry and other sciences where the purity and integrity of materials must be preserved against the effects of water vapor.
Controlling Humidity: Why Desiccation is Necessary
Ambient moisture poses a significant challenge in the laboratory, particularly when dealing with hygroscopic materials. These substances, which include many common salts and reagents, readily absorb water molecules directly from the surrounding air. This absorption can change the substance’s chemical composition, leading to a loss of purity and unpredictable results in subsequent experiments.
The presence of moisture is especially problematic for accurate quantitative measurements, such as when weighing samples. If a sample absorbs water during the weighing process, the recorded mass will be falsely elevated, compromising the analysis. Humidity can also cause material degradation, initiating unwanted chemical reactions or altering the desired crystal structure of a compound. Therefore, the controlled, dry environment provided by a desiccator is necessary to stabilize these materials.
How a Desiccator Works
A standard desiccator consists of a heavy-walled container, typically made of glass or robust plastic, paired with an airtight lid. Inside the chamber, a perforated plate or shelf sits above the lower compartment, where the active drying agent is placed. The lid creates a secure seal, often assisted by vacuum grease or a gasket, which prevents external moisture from entering the controlled space.
The core mechanism relies on a desiccant, a highly moisture-absorbing material located beneath the shelf. Common desiccants include silica gel, anhydrous calcium chloride, or Drierite, which bind the water molecules present in the air within the container. As the desiccant absorbs water vapor, the humidity level inside the desiccator drops significantly. Some desiccants also contain an indicator compound, such as cobalt chloride, which changes color to signal when the material is saturated and needs replacement.
Common Laboratory Uses
One of the most frequent uses for a desiccator is the long-term storage of moisture-sensitive chemicals and reagents. By providing a continuously low-humidity environment, the apparatus ensures that these hygroscopic compounds maintain their intended purity and reactivity over time. This application is crucial in analytical chemistry, where the exact concentration and composition of reagents are paramount for reliable results.
The desiccator is also routinely used for cooling hot samples that have been removed from a drying oven or furnace. The sample is transferred directly into the desiccator to cool down to room temperature before weighing. This procedure prevents the hot, dry sample from immediately absorbing atmospheric moisture as it cools, a process known as “cooling to constant weight.”
Desiccators also serve to protect sensitive laboratory equipment and biological specimens. Items like electrodes, delicate electronic components, and biological samples must be kept completely dry to avoid degradation or malfunction. The desiccator provides a stable, dust-free enclosure for these materials, extending their lifespan and ensuring their integrity.