Glass Desiccators

Silica gel is the most common choice. Use silica gel for general-purpose sample drying and storage. Anhydrous calcium chloride is cheaper but not suitable for use with alcohols, amines, or ketones. Phosphorus pentoxide achieves the lowest attainable humidity but is highly corrosive and cannot be regenerated.

Choose a desiccator diameter based on the largest item you need to place inside it. A 150 mm desiccator suits small samples and crucibles. A 200 to 230 mm desiccator is the most common size in analytical chemistry labs. A 300 mm desiccator is used where large items must be stored.

A standard desiccator is sufficient for most routine drying and storage tasks. Choose a vacuum desiccator if you need to remove residual solvents rapidly, dry heat-sensitive materials at low temperature, or perform outgassing before analysis.

With indicating silica gel, the colour change from blue (dry) to pink or white (saturated) tells you when the desiccant needs regeneration. Regenerate by heating at 120C for 2 to 3 hours. Always replace the desiccant before any visible moisture appears at the bottom of the desiccator.

Indicating silica gel is the best general-purpose choice for most laboratories. For very low humidity, use anhydrous calcium chloride but avoid it with alcohols, amines, aldehydes, or ketones. For the lowest achievable humidity, phosphorus pentoxide is used in specialised analytical work but is highly corrosive and cannot be regenerated.

A crucible heated in a furnace will absorb moisture from the air as it cools, adding mass and introducing systematic error into gravimetric calculations. Cooling inside a desiccator prevents this. Allow at least 20 minutes for a crucible to reach room temperature inside the desiccator before weighing.

No. Only desiccators specifically designed for vacuum use should be evacuated. Standard desiccators with flat lids may implode under vacuum. Vacuum desiccators have a borosilicate glass dome and a ground-glass stopcock. Always inspect for chips or cracks before applying vacuum.

Remove the porcelain plate and desiccant before cleaning. Wash with mild laboratory detergent and warm water, rinse with distilled water, and air-dry completely. Lightly grease the ground-glass rim after cleaning to maintain a good seal.

Slide the lid horizontally across the ground-glass rim rather than lifting it straight up. Grip the lid firmly and push it sideways with a smooth, steady motion until the seal breaks and air enters. If the lid is very stuck, gently warm the glass rim with your hands to expand it slightly.