Laboratory Glass Tubes

Test tubes have a rounded bottom for flame heating and general use. Boiling tubes have a thicker wall for vigorous heating. Culture tubes have straight sides for microbiology and incubation. Nessler tubes are tall flat-bottomed cylinders for colorimetric comparisons. Centrifuge tubes are designed to seat in a centrifuge rotor.

Standard test tubes range from 10 x 75 mm (about 3 ml) to 25 x 200 mm (about 60 ml). A 16 x 150 mm tube holding 15 to 20 ml is most versatile for school chemistry. For microbiology, 13 x 100 mm or 16 x 125 mm is standard. Choose a tube that holds 1.5 to 2 times the sample volume for safe mixing.

Glass test tubes can be closed with rubber bungs, silicone stoppers, or cotton wool plugs. Screw-cap culture tubes provide a secure seal for liquid cultures and tolerate autoclave sterilisation with the cap loosened. Ground-glass stoppers provide a chemical-resistant hermetic seal for storage.

Yes. Borosilicate glass test tubes can be autoclaved at 121 degrees C at 15 psi for 15 to 20 minutes. Fill no more than two thirds full to prevent boilover. Soda-lime glass should not be autoclaved repeatedly. Always loosen screw caps before the cycle to prevent pressure build-up.

Test tubes are slender round-bottomed tubes 16 to 18 mm wide for small-scale reactions and culture work. Boiling tubes are larger with thicker walls, typically 25 mm wide, designed for more intensive direct Bunsen burner heating. Use a test tube for routine bench work; use a boiling tube for more volume or vigorous heating.

Yes, borosilicate glass test tubes are designed for direct flame heating using a test tube holder. Hold the tube at an angle, never pointing at anyone, and move it in the flame to distribute heat evenly. Never heat a stoppered tube. Allow heated tubes to cool in a rack rather than on a cold bench surface.

Nessler tubes are matched-volume flat-bottomed glass cylinders for visual colorimetric comparison. A series of standards and an unknown sample are filled to the same volume and viewed from above against a white background. Used in water quality testing for ammonia, nitrate, iron, and other analytes. Must be used as a matched set for accurate comparison.

Autoclave at 121 degrees C at 15 psi for 15 minutes with cotton wool plugs or loose caps. Alternatively, dry heat sterilise at 160 degrees C for 2 hours with tubes wrapped in aluminium foil. Dry heat is preferred when tubes must be completely dry after sterilisation.

Glass tubes can be autoclaved, heated directly, and reused indefinitely. They resist organic solvents, strong acids, and bases. Plastic tubes (polypropylene or polystyrene) are disposable, lightweight, unbreakable, and pre-sterilised, suited to high-throughput clinical and molecular biology labs. Choose glass for chemical resistance and reuse; choose plastic for single-use sterility and convenience.