Choosing & Using a Gas Buret Correctly – Final Version
Key Takeaways
A gas buret is graduated glassware used to collect and measure gas by liquid displacement rather than to dispense a liquid.
Always start with clean, degassed confining liquid and remove bubbles before any reading to avoid systematic error.
Read the meniscus at eye level; modern digital or e-burets can reduce parallax and transcription errors.
Standard borosilicate glass withstands most laboratory chemicals, but gas burets are rated only for near-ambient pressure; high-pressure work needs reinforced metal or thick-walled glassware.
Variants include volumetric glass, digital (piston), electronic, and specialty designs such as the Tutwiler buret for on-tube titrations.
Introduction
Precise gas volume measurement is essential in stoichiometry, gas-law verification, and purity checks. A gas buret—spelled burette in UK usage—is a calibrated tube filled with a confining liquid (commonly water or non-volatile oil) attached to a reservoir. Incoming gas displaces the liquid, and the displacement equals the collected gas volume once temperature and pressure are equilibrated.
Gas vs. Liquid Burets
Stopcock location: bottom for liquid dispensing, top or side for gas collection.
Operating principle: gravity-driven outflow for liquids vs. displacement for gases.
Interchangeability: not recommended; glass thickness, graduation alignment, and valve orientation differ and affect accuracy.
Achieving Accurate Gas Measurements
Use degassed, isothermal liquid to minimise dissolved-gas errors.
Equalise internal and external pressure by adjusting the reservoir height before every reading.
Record ambient barometric pressure and temperature to convert the observed volume Vobs to standard conditions via VSTP=Vobs×Pobs760 mm Hg×273.15 KTobs.
Gas Buret Types and Applications
| Type | Distinguishing Features | Typical Use |
|---|---|---|
| Volumetric glass | Graduated tube, manual reading | Educational and routine synthesis |
| Digital (piston) | Syringe barrel, hand wheel, LCD read-out | High-precision research titrations |
| Electronic (e-buret) | Motorised piston, micro-controller | Automated QA/QC labs |
| Tutwiler gas buret | Dual stopcocks, internal titration bead | Rapid H₂S or CO₂ determinations in fuel gas |
The Tutwiler Gas Buret
Developed for field hydrogen-sulfide assays, the Tutwiler buret combines gas collection and immediate titration in one unit. A glass bead agitates the contents, allowing iodine or cadmium acetate solutions to react directly with the gas; volume change and colour shift yield concentration without sample transfer.
Cleaning and Maintenance
Rinse with deionised water followed by the confining liquid; avoid strong bases on grease-free stopcocks.
Inspect graduations for etching or duplication errors (rare but documented) before first use and after storage.
Store vertically in a padded clamp; keep PTFE or glass stopcocks lightly lubricated with silicone grease rated for the working solvent.
Frequently Asked Questions
Materials? Borosilicate glass tube with PTFE or glass plug stopcock for chemical and thermal resistance.
High pressure? No; use a metal gas buret or pressure transducer for pressures > 1 atm to prevent shattering.
Cleaning steps? Rinse, soak in mild laboratory detergent if needed, flush stopcock, dry inverted, and store clamped.
Conclusion
Correct selection and meticulous handling of a gas buret ensure reproducible gas-volume data across academic and industrial settings. By choosing the proper model, eliminating bubbles, and standardising temperature-pressure conditions, analysts can trust their quantitative results and extend the life of their equipment.