Cork Stopper, Rubber, Two Holes

Quick Answer: The Cork Stopper, Rubber, Two Holes is a tapered rubber bung with two parallel bores. A two hole rubber stopper lets two tubes pass into one vessel at once, typically an inlet such as a thistle funnel and an outlet such as a delivery tube.

An Inlet and an Outlet in One Neck

The classic school use is gas preparation. A flat-bottom or conical flask holds the solid, for example marble chips for carbon dioxide or zinc granules for hydrogen; a thistle funnel through one bore adds the acid, and a delivery tube through the other carries the gas to a gas jar or trough. The stem of the thistle funnel must reach below the liquid surface, otherwise the gas escapes back up the funnel instead of along the delivery tube.

The same stopper turns a flask into a glass wash bottle, with a short tube for blowing air in and a longer tube that reaches the bottom and ends in a jet. It also serves when a gas is bubbled through a liquid, or when a reaction flask feeds a drying tube or a second vessel in a chain.

Because the spacing is fixed by the two bores, glass that is too thick for the holes, or bent too close to the rubber, can split the thin web between them. Insert the straighter tube first and fit the bent one second.

Applications

• Preparing carbon dioxide, hydrogen or oxygen in a flask with a thistle funnel and delivery tube
• Assembling a glass wash bottle with an air inlet and a jet outlet
• Bubbling a gas through limewater or another reagent in a boiling tube
• Connecting a flask to a drying tube or second vessel in a chain of apparatus

Specifications

Assembly & Care

• Lubricate each tube with water or glycerol and fit them one at a time, holding the glass through a cloth close to the rubber.
• Point the delivery tube away from students and keep flames well clear, especially when hydrogen is being collected.
• Dismantle the apparatus after the lesson so that tubes do not bond to the rubber.
• Retire stoppers with tears between the bores, as they leak gas.

Why Choose LabEquip

Two hole stoppers are mostly bought by schools running gas preparation practicals, often with a thistle funnel and delivery tube for each bench. LabEquip stocks them in the General Lab Products range; list your flask neck sizes on the contact page.

Frequently Asked Questions

Why must the thistle funnel dip below the liquid?

The liquid forms a seal at the bottom of the funnel stem. If the stem ends above the liquid, gas escapes up the funnel into the room and little of it reaches the delivery tube or gas jar.

Which gases can be prepared with this set-up?

Any gas made from a solid and a liquid without heating, such as carbon dioxide from marble chips and dilute hydrochloric acid, hydrogen from zinc and dilute acid, or oxygen from hydrogen peroxide with a manganese dioxide catalyst.

How do I check the apparatus is airtight?

Close the end of the delivery tube, then pour water into the thistle funnel until the stem end is covered. If the water level in the funnel stays still, the joints are sealed; if it keeps falling, a joint is leaking.

Can I use it to make a wash bottle?

Yes. Fit a short tube for blowing into and a long tube that reaches almost to the base of the flask and ends in a fine jet. Blowing into the short tube forces water out through the jet.

Why did the rubber split between the two holes?

The strip of rubber between the bores is thin. Forcing an oversized tube, levering a bent tube sideways or leaving tubes in until the rubber hardens can all tear it. Lubricate the glass and choose tubes that match the bores.

Is a two hole stopper suitable for heating?

It can be used on a flask that is gently warmed, provided one tube leads to an open outlet so that pressure cannot build. Keep the rubber away from flames and very hot glass.

Last Updated: September 2026