Dessicator, Borosilicate Glass

Quick Answer: A borosilicate glass desiccator is a heavy glass vessel with a ground-flanged lid and a perforated plate above a lower chamber that holds a drying agent. It keeps samples in dry air, most often so that heated crucibles and weighing bottles can cool without absorbing moisture before they are weighed.

Cooling to Constant Mass

In gravimetric analysis a crucible or precipitate is heated, cooled and weighed repeatedly until two weighings agree. Cooling in open air would let a hot, dry sample pick up water vapour, so the cooling step takes place in a desiccator. The drying agent in the lower chamber, commonly self-indicating silica gel or anhydrous calcium chloride, keeps the enclosed air dry, and a perforated plate, usually porcelain, supports the crucibles above it.

The lid seals on a ground glass flange that is lightly greased, and it is opened by sliding it sideways rather than lifting it. Borosilicate glass copes better than ordinary soda-lime glass with warm crucibles set on the plate and with changes in room temperature, which is why it is preferred for regular analytical use. It is still not meant for red-hot items: let crucibles cool briefly on a heat-resistant tile before transferring them.

The listing spells the item Dessicator and does not say whether the lid carries a stopcock for evacuation, nor the plate diameter. A plain lid is used at atmospheric pressure; a vacuum lid allows faster drying. See the clear glass desiccator for general storage, and the plastic vacuum desiccator when breakage is the bigger concern.

Specifications

Applications

• Cooling crucibles, weighing bottles and filter crucibles between heating and weighing in gravimetric work
• Holding oven-dried primary standards, such as anhydrous sodium carbonate, until they are weighed for standard solutions
• Storing dried soil, cement or plant samples before moisture-content determination
• Keeping anhydrous salts from absorbing water between practicals

Care & Handling

• Open by sliding the lid horizontally; lifting a greased lid straight up rarely works and risks dropping it.
• Regrease the flange sparingly when the lid starts to catch, wiping off old grease first so grit does not scratch the seal.
• Replace or regenerate the silica gel when its indicator changes colour, and keep desiccant off the plate.
• Carry a loaded desiccator with both hands and a thumb on the lid, never by the knob alone.

Why Choose LabEquip

Analytical, pharmacy and soil-testing laboratories that weigh to constant mass every day need a desiccator that tolerates warm crucibles. LabEquip lists it among its chemistry lab equipment; give the diameter and lid type you need through the contact page.

Frequently Asked Questions

Why must crucibles be cooled in a desiccator before weighing?

A hot crucible cooling in room air takes up water vapour on its surface, and a warm object also disturbs a balance through air currents. Cooling in dry, enclosed air to room temperature gives a reliable, repeatable mass.

Which drying agent should I use?

Self-indicating silica gel is the most common choice because it shows when it is exhausted and can be regenerated in an oven. Anhydrous calcium chloride is cheap for general storage. Stronger desiccants such as phosphorus pentoxide are reserved for special work.

How do I open a desiccator lid that has stuck?

Push the lid sideways with steady pressure on the knob while holding the base. If it does not move, warm the flange gently with a warm cloth to soften the grease. Never lever the lid off with a tool.

Can I put a red-hot crucible straight into the desiccator?

No. Let it cool in the air for a short time on a heat-resistant tile first. Very hot objects can crack the plate or the glass, and they heat the enclosed air, which then contracts and can make the lid hard to open.

How is borosilicate better than clear glass for a desiccator?

Borosilicate glass expands much less when heated, so it tolerates warm crucibles and changes in room temperature with less risk of cracking. For storing chemicals at room temperature the difference matters less.

What grease should be used on the flange?

Use a laboratory stopcock or vacuum grease, applied as a thin, even film. Too much grease lets the lid slide off and collects dust; too little leaves a leaky seal.

Last Updated: September 2026