Bulkglasspack
Spherical round-bottom flask with a long straight neck and ground joint at the mouth
Shown configuration · flask alone / support ring, clamp, joint clip and contents not shown

Reaction & distillation glassware

Round-bottom Flask

A spherical boiling flask in borosilicate 3.3 with an ISO 383 conical joint, made to ISO 4797 for reflux, distillation and any duty involving vacuum or vigorous boiling.

ISO 4797 with ground joint24/29 and 29/32 referencesSphere resists vacuum
Stock status
In stock
Lead time
2–3 weeks
FOB price / pc
$0.75 - $1.05
MOQ
2,000 pcs
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Final availability, dimensions, materials, assembled components and commercial terms are confirmed against the selected drawing and approved sample.

No corners to stress

Even wall carries pressure difference well

Heats without hot spots

Curved base suits a mantle exactly

Needs a support

It will not stand on a bench unaided

Round-bottom Flask profile

The shape exists because a sphere is the only vessel with nowhere for stress to gather.

Joints, heating & the practical consequences of a sphere

What to settle before a round-bottom flask reaches a rig.

Reflux, distillation and rotary evaporation put glass under a pressure difference while heating it unevenly. A sphere handles both better than any other form: the wall is in pure membrane stress and a heating mantle wraps it completely. The price is that it cannot stand up, which is why round-bottom flasks come with a support requirement rather than a base.

01

The joint is the interface to everything else

ISO 4797 flasks carry ISO 383 conical joints so condensers, stillheads and adapters connect without tubing. The size — 14/23, 19/26, 24/29, 29/32 — is what determines whether a flask joins the apparatus a laboratory already owns. Buying capacity without specifying the joint reliably produces a cupboard of flasks that fit nothing, which is a slow and expensive mistake.

02

A mantle fits the curve; a hotplate does not

Heating mantles are made to match standard spherical radii, so the glass is in contact over most of its lower surface and heats evenly. On a flat hotplate a round flask touches at a point, which produces a local hot spot, bumping and eventually a crack. Matching mantle size to flask size is not a convenience, it is the condition under which the flask is safe.

03

One neck or several depends on the chemistry

A single-neck flask suits reflux and rotary evaporation. Two- and three-neck versions let a condenser, a thermometer and an addition funnel work at once, which is what any controlled addition or temperature-following reaction requires. Extra necks are angled rather than vertical, and their sizes are usually specified smaller than the central one.

04

Never heat a closed system, and never trust a stuck joint

A ground joint sealed by heat, by crystallized product or by a clip left in place turns a heated flask into a pressure vessel. Standard practice keeps a vent path open at all times and uses joint clips deliberately rather than habitually. Where a reaction produces gas, the vent is designed into the apparatus rather than left to whichever joint happens to leak.

05

Support it before you fill it

A round-bottom flask lies on its side on a bench and rolls off it. Cork rings, clamped stands and mantle nests are part of the specification of the workstation, not optional accessories. Most laboratory breakages of these flasks happen when a full one is set down for a moment, which is the moment the shape was never designed for.

06

Wall thickness is a compromise, not an upgrade

Thicker glass survives more knocks and resists more pressure difference, and it also stores more thermal stress and heats more slowly. Standard-wall flasks are the right default for atmospheric reflux and rotary evaporation; heavy-wall versions belong on vacuum work where the pressure difference is sustained. Fitting a heavy-wall flask everywhere costs heating performance and gains little.

Application guide

It cannot stand up, and that is deliberate.

A fully spherical base distributes heat and pressure with no flat section to concentrate stress, which is precisely why it tolerates conditions other flasks do not and why it always needs a support. These are development directions confirmed with the actual method.

Round-bottom Flask used for flasks heated for hours in a mantle in a reflux and distillation setting

Reflux and distillation

Flasks heated for hours in a mantle

For a chemist holding a reaction at reflux through an afternoon, with the spherical body sitting in a mantle that matches its curve. The heat arrives evenly over the whole wetted surface and there is no flat base to develop a hot spot, which is why the shape became standard for anything left boiling.

  • Match the mantle to the flask curve
  • Confirm even contact with the heater
  • Clamp securely at the neck
Round-bottom Flask used for a flask that cannot be put down in a crowded benches setting

Crowded benches

A flask that cannot be put down

For anyone working at a bench where space is short and a flask released for a second rolls into something. It needs a clamp, a stand or a cork ring at every stage, including while it cools and while it is being poured out, so the supports belong in the bench layout rather than being improvised.

  • Provide a ring or clamp at every stage
  • Plan for cooling while supported
  • Confirm the clamp suits the neck
Round-bottom Flask used for geometry that resists external pressure in a vacuum work setting

Vacuum work

Geometry that resists external pressure

The sphere is the strongest possible shape against uniform external pressure, which is why chemists reach for this flask for rotary evaporation and other reduced-pressure work. Any scratch, chip or star crack undermines that strength locally and makes the vessel genuinely unsafe to evacuate, however sound the rest of it looks.

  • Inspect for scratches before vacuum use
  • Confirm the rating for the pressure applied
  • Reject any flask with a star crack

Applications describe development directions. Method suitability, thermal and vacuum performance and laboratory outcomes are confirmed for the selected program.

Common questions

Round-bottom Flask questions

Joint size and heating method cause most of the trouble with these flasks.

Can we heat one on a hotplate?

Not directly. A spherical flask touches a flat plate at a point, which makes a local hot spot, causes bumping and eventually cracks the glass. Heating mantles are made to match standard flask radii so the glass is warmed over most of its lower surface. Matching mantle size to flask size is a safety condition, not a matter of efficiency.

Why a round bottom rather than a flat one?

Because a sphere has nowhere for stress to concentrate. Under reduced pressure the wall works in pure membrane stress rather than bending, so it tolerates the pressure difference that would collapse a flat base. It also matches a mantle exactly. The cost is that it cannot stand up, which is why supports are part of the workstation specification.

Should we buy heavy-wall flasks throughout?

Rarely worth it. Thicker glass takes more knocks and more pressure difference, and it also stores more thermal stress and heats more slowly. Standard wall is the right default for atmospheric reflux and rotary evaporation; heavy wall belongs where a sustained vacuum is applied. Fitting heavy wall everywhere costs heating performance for a benefit most work never uses.

Should it be supported before or after filling?

Before, always. A round-bottom flask cannot stand on its own, and a full one set down for a moment is a spill and a breakage at once. Clamp or seat it in a ring first, then fill — the sequence matters more than it sounds.

Next step

Send us the Round-bottom Flask brief.

Tell us the product, fill volume, closure preference and destination market. We will come back with the matching drawings, available configurations and a sample plan before anything is quoted.

Request a project quote Talk to the team
  • 01Send the briefProduct, volume, closure and market
  • 02Get the optionsMatching drawings and configurations
  • 03Approve the sampleConfirm the pack before production