U-Shaped Drying Tube, Plain

This plain U-shaped drying tube is used to dry gases or protect moisture-sensitive reactions by holding a solid desiccant such as calcium chloride.

Key Features

• Glass: Quality borosilicate 3.3 glass.
• Heat resistance: Handles high temperatures and rapid thermal shock, with a strain point of about 520°C.
• Chemical durability: Highly resistant to water, neutral and acid solutions, and most organic solvents.
• Clarity: Clear glass makes it easy to see the desiccant change colour (for example when silica gel is saturated).
• Design: Plain U-shape

In school labs, U-shaped drying tubes are basic apparatus for removing water vapour from gases. They're usually filled with a solid desiccant (drying agent) such as anhydrous calcium chloride or silica gel.

1. Preparing Dry Gases

When students make gases in the lab (like oxygen, hydrogen or carbon dioxide), the gas often passes through water on the way. The U-tube removes that moisture. For example, when preparing dry hydrogen, the gas passes through a U-tube of calcium chloride before being collected or used in another reaction.

2. Protecting Moisture-Sensitive Reactions

Some reactions fail if even a little humidity from the air gets into the flask. A drying tube fitted to the top of a reflux condenser or reaction flask lets the system "breathe" (so pressure can't build up) while making sure any air entering is bone dry.

3. Quantitative Analysis (Mass Change)

In advanced school chemistry, U-tubes are used to measure how much water a combustion reaction produces. Students weigh the tube before and after. The increase in mass shows exactly how much water the desiccant absorbed, so they can work out the hydrogen content of the sample.

4. Preventing Suck-Back

In experiments that involve heating and gas collection, a U-tube can act as a safety buffer. Its extra volume helps stop water from the trough being sucked back into a hot test tube, which would crack the glass.

5. Demonstrating Desiccants

Teachers use U-tubes to show how materials react with moisture. With blue silica gel in the tube, students can watch it turn pink as it absorbs moisture from a stream of damp air, which shows hydration clearly.

Tip for School Labs

To stop the desiccant falling out of the arms or blocking the gas flow, put small plugs of glass wool or cotton wool at both ends of the U-tube before filling it.