Cork Stopper, Extra Soft, Two Holes

Quick Answer: This two hole cork stopper is an extra-soft tapered rubber stopper bored with two parallel holes. It seals a flask or bottle while carrying two pieces of glass, typically an inlet and an outlet, as in gas preparation and wash-bottle set-ups.

Inlet and Outlet in One Stopper

Many classic set-ups need two openings in one neck. For preparing carbon dioxide, marble chips sit in a conical flask, dilute hydrochloric acid is added through a thistle funnel in one hole, and the gas leaves through a delivery tube in the other. In a gas-washing arrangement, a long tube dips below the liquid while a short tube takes gas out above it. Respiration experiments with germinating seeds use the same idea to draw air through limewater.

With two holes, the rubber between them is the weak point. The extra-soft compound seals easily, but it also tears more readily, so both tubes should be lubricated and eased in one at a time without levering sideways. Like the one hole version, this series is rubber despite the word cork in the title, so it suits aqueous acids and alkalis but not organic solvents.

Specifications

Applications

• Preparing carbon dioxide or hydrogen with a thistle funnel and delivery tube
• Gas-washing and drying trains with a long inlet and short outlet tube
• Respiration experiments drawing air through limewater
• Siphon and aspirator arrangements that need air and liquid lines

Care & Handling

• Insert the longer tube first, then the shorter one, each lubricated and eased in with a twisting motion.
• Do not bend the tubes once fitted; sideways force splits the rubber between the holes.
• Check the seal by blowing gently into one tube with the other closed; bubbles or hissing show a leak.
• Wash stoppers after acid work and let them dry before storage.

Why Choose LabEquip

Chemistry teachers use two hole stoppers in almost every gas preparation practical, so schools often keep them in several sizes. LabEquip lists this extra-soft grade in the General Lab Products range; send your flask neck sizes through the contact page.

Frequently Asked Questions

What is a two hole stopper used for?

Any set-up that needs an inlet and an outlet through one neck, such as gas preparation with a thistle funnel and delivery tube, or a gas-washing bottle.

Why must the thistle funnel dip below the liquid?

If the funnel’s end is above the liquid, gas escapes up the funnel instead of through the delivery tube. Keeping it below the surface forces gas out the delivery tube.

How do I test the stopper for leaks?

Fit the stopper into the flask, close one tube with a finger and blow gently into the other. A hiss, or bubbles when a little water is dabbed around the joint, shows a leak.

Why did the stopper split between the holes?

The rubber there is thin, and forcing or levering glass tubes stretches it. Lubricate the tubes, insert them one at a time and avoid bending them once fitted.

Is it suitable for making hydrogen in class?

It is commonly used for this, but hydrogen forms explosive mixtures with air. Keep flames away, collect the gas as the practical instructs and test only small test tubes of gas.

Can I use it with organic solvent vapours?

It is rubber, which swells in many organic solvents. For solvent work, choose a cork, glass or PTFE closure.

Last Updated: September 2026