Burette, Straight Bore Glass Key

Quick Answer: A straight bore glass key burette is a graduated glass tube with a glass stopcock at its lower end, in which the hole through the key runs straight across. Turning the key lines the bore up with the burette to deliver titrant, or turns it across to stop the flow.

The Classic Titration Burette

For generations of chemistry students, the straight bore glass key burette has been the burette of the acid-base titration: a long graduated tube clamped vertically, a conical flask on a white tile below, and a glass tap turned with one hand while the other swirls the flask. The straight bore is the simplest stopcock design. The hole runs straight through the key, so a quarter turn takes it from shut to fully open, and any position in between regulates the rate.

The key and barrel are both ground glass. They need a thin film of stopcock grease to turn smoothly and seal, and they are usually matched to each other during manufacture, so keys are not freely swapped between burettes. The all-glass construction resists acids, oxidising agents and most solvents, and the stopcock can be seen through, which helps when checking for trapped bubbles.

Its weak point is alkali. Sodium hydroxide left in the stopcock dries into a glassy film that locks the key, so after an alkali titration the burette should be drained and rinsed with water before it is put away. A strip of paper placed between key and barrel for storage is an old laboratory habit that keeps the two surfaces from sticking.

Specifications

Applications

• Acid-base titrations such as hydrochloric acid against sodium carbonate with methyl orange
• Standardising sodium hydroxide against potassium hydrogen phthalate using phenolphthalein
• Precipitation titrations with silver nitrate, such as chloride determination
• Teaching burette technique: filling, removing bubbles, reading and recording titres

Care & Handling

• Rinse the burette with a few cubic centimetres of the titrant before filling, so leftover water does not dilute it.
• Remove the filling funnel before taking the first reading; drips from it change the volume in the burette.
• Drain and rinse after alkali titrations, and store the key loosened or with a paper strip in the joint.
• Keep keys with their own burettes, labelled if several are stored together.

Why Choose LabEquip

Schools and colleges buy straight bore glass key burettes in class sets for the core titration practicals of the chemistry syllabus. LabEquip lists them in the chemistry lab equipment range, and for alkali-heavy work the PTFE key burette is the greaseless alternative. Send quantities through the contact page.

Frequently Asked Questions

What does straight bore mean on a burette stopcock?

It means the hole through the stopcock key runs straight across it. When the key is turned parallel to the burette, the hole lines up with the burette and tip and the liquid flows; a quarter turn blocks the flow.

How do I grease a glass key correctly?

Clean and dry the key and barrel, apply two thin rings of stopcock grease on the key, one on each side of the hole, then insert and rotate it until the joint looks clear. Wipe away any grease that reaches the bore.

Why do titration results need concordant titres?

One titration can be affected by a missed drop or a misread scale. Repeating until two or more titres agree closely, commonly within 0.10 cubic centimetres in school practicals, shows the result is reliable before an average is taken.

How do I get rid of the air bubble below the stopcock?

Fill the burette, then open the key fully for a moment over a beaker so the fast flow sweeps the bubble out of the tip. Refill and take the initial reading once the tip is full of liquid.

Why should the burette not be left with sodium hydroxide in it?

Alkali attacks the ground glass surfaces and, as it dries, can cement the key to the barrel. Drain the burette after use and rinse it with distilled water, because a seized key is often impossible to free without breaking the burette.

Should the initial reading always be zero?

No. It only needs to be recorded accurately. Starting at or near zero is convenient, but subtracting the initial reading from the final reading gives the titre whatever the starting point.

Last Updated: September 2026