Tubes, Delivery

Quick Answer: A delivery tube is a length of glass tubing bent to shape, such as an L or U, that carries gas from a reaction vessel to where it is collected or tested. It passes through a hole in a rubber bung or cork on the generating flask or test tube.

Carrying Gas From Flask to Jar

Almost every gas preparation in school chemistry needs a delivery tube. Hydrogen from zinc and dilute acid, carbon dioxide from marble chips and hydrochloric acid, and oxygen from hydrogen peroxide with manganese(IV) oxide all leave the flask through a bent glass tube in its bung and travel to a gas jar over water, a syringe or a test tube of limewater. The bend and length decide whether the gas can reach under a beehive shelf in a trough, up into an inverted jar or down to the bottom of an upright one.

Glass tubes are clear, so a teacher can see liquid creeping back towards a hot flask, and they resist the acids, alkalis and gases met in school work. Common forms are the right-angle L tube, the U tube and tubes bent twice for upward or downward delivery. This listing covers delivery tubes generally, so the shape, length and bore should be confirmed when ordering.

The weak point is the joint with the bung. A common cause of cuts in school laboratories is pushing glass tubing through rubber, when a tube snaps and the broken end is driven into the hand. Wetting the tube with water or glycerol, holding it close to the bung and protecting the hand with a cloth prevent most of these injuries.

Care & Handling

• Take the tube out of the water before you stop heating, or cold water will be sucked back into the hot vessel and crack it.
• Lubricate with water or glycerol and twist gently when inserting into a bung; never force it.
• Fire-polish or inspect cut ends, because a sharp end cuts both rubber and hands.
• Rinse tubes after use so acid spray and limewater deposits do not dry inside.

Applications

• Collecting gases over water in a trough with a beehive shelf
• Bubbling carbon dioxide through limewater to identify it
• Upward or downward delivery of gases that dissolve in water, such as ammonia or hydrogen chloride
• Leading gases from heated solids, such as carbon dioxide from copper(II) carbonate, into test reagents

Specifications

Why Choose LabEquip

Schools buy delivery tubes in class quantities for gas-preparation practicals and replace them regularly as tubes break. LabEquip lists them in the chemistry lab equipment range, where they pair with vessels such as the flat bottom boiling flask; send the shapes and quantities needed through the contact page.

Frequently Asked Questions

What causes suck-back and how is it prevented?

When heating stops, the gas in the hot vessel cools and contracts, and water from the trough is pulled back along the tube into the hot glass, which can crack it. Lift the tube out of the water before removing the heat.

How do I push glass tubing into a rubber bung safely?

Wet the end of the tube with water or glycerol, wrap your hand in a cloth, hold the tube close to the bung and twist it in gently. Never push from the far end of the tube or use force.

Which delivery method suits which gas?

Gases that are only slightly soluble, such as oxygen and hydrogen, are collected over water. Soluble gases lighter than air, such as ammonia, go into an inverted jar by upward delivery, and denser ones such as hydrogen chloride into an upright jar by downward delivery.

Can glass tubing be bent in the laboratory?

Yes, soda glass tubing can be softened in a wide flame, using a fishtail attachment on the burner, and bent to a smooth curve. A narrow flame gives a kinked, weak bend, so rotate the tube evenly while heating.

Why use glass instead of rubber tubing?

Glass is rigid, transparent and resistant to most chemicals, so it holds its shape under water and shows the gas and liquid inside. Rubber or plastic tubing is often added as a flexible link between two glass sections.

How far should the tube go into the collecting jar?

For collection over water, the end only needs to sit under the mouth of the jar. For upward or downward delivery, the tube should reach nearly to the far end of the jar so the air is pushed out completely.

Last Updated: September 2026