Reflux apparatus symbol

A flask with a vertical condenser above it, in an apparatus diagram.

Also known as: Reflux, Flask with a tube on top

ScientificQuiet profile

Meanings

A flask with an upright condenser is reflux: the mixture boils and the vapour condenses back into it. Drawing the condenser vertical rather than angled is the whole point, and an angled one would be distillation instead.

Common modern usageVerified fact
Depicts apparatus for heating a mixture at its boiling point while returning the vapour as liquid, so nothing is lost over a long reaction.
Contexts: Laboratory
Common modern usageVerified fact
Is distinguished from distillation by the condenser being vertical rather than angled: one returns the condensate and the other collects it.
Contexts: Laboratory

Visual description

A round-bottomed flask drawn in outline with a long vertical tube rising from its neck, the tube shown with an outer jacket and two side ports.

A fuller structured visual breakdown is not yet documented for this symbol.

Confidence

IdentityModerate confidence: Moderate confidence because the identity is documented in encyclopedic references, but only a single source has been found so far.
Historical originLow confidence: Low confidence because the historical origin is documented in encyclopedic references, but only a single source has been found so far, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useModerate confidence: Moderate confidence because the current use is documented in encyclopedic references, but only a single source has been found so far.
Visual matchModerate confidence: Moderate confidence because the visual match is documented in encyclopedic references, but only a single source has been found so far.

Sources

Reflux
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for what a symbol denotes in ordinary scientific practice and for which fields reuse it, never for a claim that any body assigns the letter its meaning.

Last reviewed 2026-07-31

Part of

Chemical equation and structure notation

Help improve this page

Meanings

Common modern usageVerified fact

Depicts apparatus for heating a mixture at its boiling point while returning the vapour as liquid, so nothing is lost over a long reaction.

Contexts: Laboratory

Common modern usageVerified fact

Is distinguished from distillation by the condenser being vertical rather than angled: one returns the condensate and the other collects it.

Contexts: Laboratory

Confidence

IdentityModerate confidence: Moderate confidence because the identity is documented in encyclopedic references, but only a single source has been found so far.
Historical originLow confidence: Low confidence because the historical origin is documented in encyclopedic references, but only a single source has been found so far, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useModerate confidence: Moderate confidence because the current use is documented in encyclopedic references, but only a single source has been found so far.
Visual matchModerate confidence: Moderate confidence because the visual match is documented in encyclopedic references, but only a single source has been found so far.