Desiccators Revised: 4/10/12 DESICCATORS
A traditional desiccator is a glass bowl and lid each with thick glass rims that permit a seal when
greased. Desiccant (a hygroscopic chemical that absorbs water out of the air) is placed beneath
the perforated ceramic disk. A sample in a beaker or crucible is placed on the top of this disk.
The purpose of the desiccator is to either dry a chemical or keep a chemical from becoming
“wet” from atmospheric humidity (water in the air).
Grease rim Ceramic Disk Dessicant (drying agent) Figure 1. Desiccator
Common desiccants are CaSO4 (Drierite), silica gel, MgSO4, and P2O5. Drierite is used quite
frequently because it changes from blue to pink as it absorbs water. Once pink, Drierite can be
dried (regenerated) by placing it in an oven set above 100°C for at least 24 hours.
Room temperature reagents and samples (typically powders or crystals) are placed in an open
container on top of the ceramic disk and the lid is closed. Always place reagents back into the
desiccator immediately so they remain dry. Avoid placing hot samples in a desiccator as they
can raise temperature resulting in an increase in the pressure of the trapped air. The lid could be
disturbed, opening the desiccator.
Use care when opening and closing the desiccator. The lid is heavy and the grease prevents
simply lifting it away from the bowl. The lid must be slid in an even, slow horizontal motion.
Only push the lid halfway off – giving just enough room to put in or take out your sample. Make
sure you always have one hand on the lid until it is completely closed. Removing the lid
completely and placing it on the countertop will transfer grease to the counter and dirt to the lid,
compromising the seal when the lid is placed back on the bowl.