Quick Answer: A screw type glass key burette is a graduated titration burette whose glass stopcock key works with a screw fitting instead of being a plain push-fit plug. Depending on the pattern, the screw either retains the key in its barrel or advances it to regulate flow, and the titrant touches only glass.
What the Screw Adds to a Glass Stopcock
A plain glass-key burette relies on a greased, tapered key that is simply pushed into its barrel, and it can loosen, turn out of position or drop out during cleaning. The screw type glass key burette adds a threaded fitting to the stopcock. In supplier catalogues the term covers two arrangements: a glass key held in place by a screw-on retaining fitting, and a glass screw-thread valve whose spindle is turned to open the flow gradually. The listing does not say which pattern this is, so confirm it when ordering.
Whatever the pattern, the flow path is glass. That matters for oxidising titrants such as potassium permanganate and potassium dichromate, and for iodine solution, which attack rubber and so rule out a Mohr burette with a rubber tube and pinch clip. Glass is also easy to inspect: a trace of brown manganese dioxide or a crystal lodged in the bore is visible and can be cleaned out.
The trade-off with a glass key is maintenance. Glass-on-glass surfaces need a thin film of stopcock grease to turn smoothly and seal, and alkaline solutions should not be left standing in the burette.
Specifications
| Item | Graduated burette with screw type glass stopcock key |
| Flow path | All glass; no rubber tubing in contact with the titrant |
| Screw function | Retains or regulates the glass key, depending on pattern |
| Lubrication | Thin film of stopcock grease on the glass-to-glass surfaces |
| Stopcock pattern and capacity | Confirm at enquiry |
Applications
- Potassium permanganate titrations of iron(II) salts or oxalic acid
- Potassium dichromate titrations with a redox indicator
- Iodine and iodometric titrations in school and college analysis
- Acid titrants such as hydrochloric or sulfuric acid in acid-base practicals
Care & Handling
- Apply grease sparingly in two thin bands on the key, away from the bore, then turn the key until the joint looks clear without streaks.
- Remove brown manganese dioxide stains with a little acidified hydrogen peroxide or oxalic acid solution, wearing gloves, then rinse well.
- Do not leave alkaline solutions in the burette; drain and rinse it at the end of the lesson.
- Keep each key with its own burette, since glass keys are ground to fit their barrel and are rarely interchangeable.
Why Choose LabEquip
Chemistry teachers who run permanganate and iodine titrations need burettes with no rubber in the flow path, and the screw type glass key is one of the all-glass options. LabEquip lists it beside the straight bore glass key burette in the chemistry lab equipment range; ask about the stopcock pattern through the contact page.
Frequently Asked Questions
Why can’t potassium permanganate be used in a burette with a rubber tube?
Permanganate is a strong oxidising agent that reacts with rubber, which lowers its concentration and damages the tube. A burette with an all-glass stopcock avoids any contact with rubber.
How is this different from a straight bore glass key burette?
Both have glass keys. The straight bore type has a plain tapered key pushed into its barrel, while the screw type adds a threaded fitting that either retains the key or regulates flow. The exact screw arrangement should be confirmed when ordering.
How much grease should a glass key have?
Only a thin film. Too much grease creeps into the bore and tip, where it blocks the flow or makes drops cling. Too little lets the key stick and leak. A well-greased joint looks transparent with no streaks.
How do I read a coloured titrant such as permanganate?
The bottom of the meniscus is hard to see through a deep purple solution, so read the top of the meniscus instead, and read it the same way for both the initial and the final readings.
What should I do if the glass key is stuck?
Do not force it. Warm the barrel gently with warm water, tap the key lightly with a wooden handle, or soak the stopcock in warm detergent solution. Wear gloves, since a burette that breaks under force can cause deep cuts.
Can the burette be dried in an oven?
Remove the key first, then let the burette drain dry upside down or dry it at a low oven setting. Avoid strong heating, which can affect volumetric glassware, and do not heat it with the key in place.
Last Updated: September 2026
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