Flask, Round/Flat Bottom (Clear Glass)

Quick Answer: This listing covers a clear glass flask with either a round or a flat bottom, both with a spherical body and a narrow neck. The round or flat bottom flask is used for gentle heating, preparing gases, dissolving solids and holding solutions in school and college laboratories.

Choosing Between the Two Bases

One listing covers both base shapes, so the choice belongs to the buyer. A round base is the stronger shape and heats most evenly, but it cannot stand alone and must sit in a cork ring, a heating mantle or a clamp. A flat base stands on the bench, a gauze or a hot plate, which suits simple set-ups in school practicals, but it is weaker and must never be put under vacuum.

The title specifies clear glass without naming the composition. Clear glass flasks sold alongside borosilicate ones are usually the ordinary soda-lime type, well suited to observation, storage, solution making and mild warming, but less tolerant of sudden temperature changes than borosilicate. For reflux, distillation or strong heating, compare the boiling flasks listed as round bottom and flat bottom, and confirm the glass type of whichever listing you choose.

State the base shape, capacity and neck form when ordering, since none of these is fixed in the listing.

Specifications

Applications

• Gas generation in school practicals, with a flat bottom flask standing on the bench and acid added through a funnel
• Showing the expansion of a heated liquid, using a flask of coloured water with a bung and a narrow glass tube
• The ammonia fountain experiment, which uses a dry round bottom flask inverted on a stand
• Holding and swirling solutions during preparation, where the narrow neck limits splashing

Care & Handling

• Warm clear glass gradually over a gauze, never in a direct flame, and let it cool in air.
• Keep round bottom flasks in cork rings, both on the shelf and on the bench.
• Never connect a flat bottom flask to a vacuum pump, and do not evacuate even a round one if the glass shows scratches.
• Clean with a curved bottle brush and warm detergent, then rinse with distilled water.

Why Choose LabEquip

Schools that mainly need flasks for demonstrations, gas preparation and solution work often choose clear glass for everyday classes. LabEquip lists both base shapes under this chemistry lab equipment listing; say which shape and size you need through the contact page.

Frequently Asked Questions

Which should I choose, a round or a flat bottom?

Choose a round bottom for boiling, reflux, distillation and anything under reduced pressure, because the sphere spreads heat and stress evenly. Choose a flat bottom when the flask must stand on its own for gas preparation, demonstrations or storage.

Is clear glass the same as borosilicate?

Not necessarily. Clear simply describes transparent, untinted glass. Borosilicate is a particular composition with low thermal expansion; clear glass listed separately from borosilicate is usually soda-lime glass, which is more sensitive to rapid heating and cooling.

How is the fountain experiment set up with this flask?

A dry round bottom flask is filled with ammonia, closed with a bung carrying a jet tube, and inverted with the tube dipping into water containing an indicator. Ammonia dissolves so readily that water is drawn up and sprays into the flask as a coloured fountain.

Can a flat bottom flask stand directly on a hot plate?

It can stand on one, but warm it gradually at a low setting, since a flat glass base heats unevenly and clear glass tolerates sudden temperature change poorly. A round bottom flask in a heating mantle is the safer arrangement for strong heating.

Why can’t a flat bottom flask be used under vacuum?

Atmospheric pressure pushes on every part of an evacuated vessel. A sphere shares that load evenly, but a flat panel flexes and concentrates stress at its edge, where the glass can crack or implode.

What stopper fits this flask?

The neck form is not fixed in the listing, so it may take a rubber bung or a ground glass stopper. Choose a rubber bung that enters about a third to a half of its length into the neck, which seals well and can still be removed easily.

Last Updated: September 2026