Combustion Tube

Quick Answer: A combustion tube is a straight, heat-resistant tube, made of hard glass, quartz or ceramic depending on the temperature needed, inside which solids are heated strongly while a gas such as air, oxygen, hydrogen or nitrogen flows through, usually with the sample held in a combustion boat.

Heating in a Flowing Gas

Some reactions need a solid to be heated in a controlled atmosphere rather than open air: an oxide reduced by hydrogen, a metal oxidised in oxygen, or a sample dried under nitrogen. The tube provides that space. Gas enters at one end through a bung and inlet tube, passes over the heated sample, and leaves at the other end, where it is burned off at a jet or vented.

The tube material decides how hot it can go. Borosilicate glass handles moderate burner heating; quartz or fused silica is used for higher temperatures and in tube furnaces; porcelain and alumina tubes serve furnace work at still higher temperatures. The title does not give this tube’s material, length or bore, so these should be settled before ordering.

The sample normally sits in a combustion boat pushed into the middle of the tube. When hydrogen or natural gas is used, air must be flushed out before any flame is applied, and the exit gas tested for purity before it is lit, because a hydrogen and air mixture in a hot tube can explode.

Specifications

Applications

• Reducing copper(II) oxide with hydrogen or natural gas to determine its formula.
• Heating metals or metal oxides in a stream of air or oxygen.
• Drying or heating samples under nitrogen in a tube furnace.
• Passing steam over heated iron wool in a demonstration of metal and steam reactions.

Safe Set-Up and Care

• Warm the tube gradually along its length before concentrating the flame under the sample.
• Flush the air out with the working gas before heating whenever hydrogen or fuel gas is used.
• Let the tube cool with the gas still flowing, so the hot product does not re-oxidise.
• Clean out deposits with a long brush, and inspect the tube for cracks or cloudiness before reuse.

Why Choose LabEquip

Colleges running quantitative inorganic practicals and labs with tube furnaces buy these tubes together with matching boats. LabEquip lists this tube in General Lab Products; tell us the material and size you need, or the furnace it must fit, through the contact page.

Frequently Asked Questions

What is a combustion tube used for?

It is used to heat a solid strongly while a gas flows over it, for reductions, oxidations and heating under an inert gas. The sample usually sits in a boat inside the tube.

Which material should the tube be made of?

Borosilicate glass suits moderate heating over a burner. For red heat and tube furnaces, quartz or ceramic tubes are used, because glass softens at those temperatures.

Why must air be flushed out before heating with hydrogen?

A mixture of hydrogen and air can ignite explosively. Passing hydrogen through first and testing a sample of the exit gas for purity makes sure no air remains before any heat is applied.

Why let the tube cool with gas still flowing?

In a reduction, the hot metal product can react with air again if air gets in while it is hot. Keeping the gas flowing until the tube is cool protects the product and gives a correct final mass.

How does the sample go into the tube?

It is weighed into a combustion boat, which is pushed into the middle of the tube with a glass rod. After heating it is drawn out with a hooked wire.

How is the tube connected to the gas supply?

One end is closed with a bung carrying a short inlet tube joined by rubber tubing to the gas supply. The other end carries a bung with an outlet tube drawn out to a jet, where excess gas is burned off or vented.

Last Updated: September 2026