Distillation Assembly, Steam

Quick Answer: A steam distillation apparatus is a glass assembly in which steam from a separate generator is passed through a mixture, carrying volatile, water-immiscible compounds over into a condenser at temperatures below 100 °C. It is used to extract essential oils from plant material and to purify organic compounds that would decompose at their own boiling points.

Why Steam Lowers the Boiling Temperature

When two liquids that do not mix are heated together, each exerts its own vapour pressure regardless of the other. The mixture boils when the two vapour pressures together equal atmospheric pressure, which happens below the boiling point of either liquid alone. Blowing steam through a flask containing an oil or an organic compound therefore makes it distil with the water at under 100 °C, even when its own boiling point is well above 200 °C.

A typical steam distillation assembly has three stages. A generator flask boils water and carries a long safety tube dipping into the water, which acts as a pressure release if the steam path blocks. A delivery tube reaching nearly to the bottom of the sample flask bubbles steam through the mixture, and a condenser followed by a receiver collects the milky distillate of water and oil, which separates on standing.

The listing does not give the parts included, joint type or flask sizes. Separating the oil from the water afterwards is usually done in a separating funnel or by solvent extraction. For a general-purpose set, compare the simple distillation assembly, and for continuous solvent extraction of solids see the Soxhlet extraction apparatus.

Specifications

Applications

• Extracting limonene from orange or lemon peel in organic chemistry practicals
• Isolating eugenol-rich clove oil from crushed cloves
• Separating 2-nitrophenol, which is steam-volatile, from 4-nitrophenol after nitration of phenol
• Pharmacognosy practicals on volatile oils from spices and leaves in pharmacy colleges

Care & Handling

• Check that the safety tube dips below the water in the generator before heating, and never close it off.
• Warm the sample flask gently as well, so that steam does not condense in it and flood the mixture.
• Keep the condenser water flowing strongly; steam carries a much larger heat load than an ordinary distillation.
• Disconnect the steam line from the sample flask before turning off the heat, so the mixture is not sucked back into the generator.

Why Choose LabEquip

Pharmacy colleges, food science departments and natural product researchers need a steam distillation apparatus for work on volatile oils. LabEquip supplies the assembly within its chemistry lab equipment; list the parts and sizes you require on the contact page.

Frequently Asked Questions

Why does steam distillation work below 100 °C?

For two immiscible liquids the vapour pressures add together, and boiling occurs when the total reaches atmospheric pressure. Because water contributes most of it, the mixture boils below 100 °C, even for compounds that boil far higher on their own.

Which compounds can be steam distilled?

Compounds that are volatile in steam, immiscible or only slightly soluble in water, and stable when hot and wet. Essential oils such as limonene and eugenol, and 2-nitrophenol, are classic examples.

What is the safety tube on the steam generator for?

It is an open tube dipping into the water. If the delivery line blocks and pressure rises, water is pushed up the tube instead of the flask bursting, and a sudden rise of water in it warns that something is blocked.

Why is the distillate milky?

The oil and water condense together as tiny droplets that have not yet separated. On standing, or after adding salt, the droplets merge into a separate layer that can be drawn off or extracted with a solvent.

Can I add water to the flask instead of using a generator?

For small, simple work, boiling plant material directly with water in the flask is a common shortcut, often called hydrodistillation. A separate steam generator gives better control and avoids charring material on the hot flask base.

Why is 2-nitrophenol steam-volatile but 4-nitrophenol is not?

In 2-nitrophenol the hydroxyl and nitro groups form a hydrogen bond within the same molecule, so it bonds little with water and is volatile. 4-nitrophenol forms hydrogen bonds between molecules and with water, which holds it in the flask.

Last Updated: September 2026