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How to Make Liquid Oxygen or Liquid O2

Simple Way to Prepare Liquid Oxygen


Liquid oxygen is blue.

Liquid oxygen in an unsilvered dewar flask. Liquid oxygen is blue.

Warwick Hillier, Australia National University, Canberra

Liquid oxygen or O2 is an interesting blue liquid that you can prepare quite easily yourself. There are several ways to make liquid oxygen. This one uses liquid nitrogen to cool oxygen from a gas into a liquid.


  • cylinder of oxygen gas
  • 1-liter Dewark of liquid nitrogen
  • test tube (approximately 200-ml)
  • rubber tubing
  • glass tubing (to fit inside test tube)


  1. Clamp a 200-ml test tube so that it will sit in a bath of liquid nitrogen.


  2. Connect one end of a length of rubber tubing to an oxygen cylinder and the other end to a piece of glass tubing.


  3. Place the glass tubing in the test tube.


  4. Crack open the valve on the oxygen cylinder and adjust the flow rate of the gas so that there is a slow and gentle flow of gas into the test tube. As long as the flow rate is slow enough, liquid oxygen will begin to condense in the test tube. It takes approximately 5-10 minutes to collect 50 mL of liquid oxygen.


  5. When you have collected sufficient liquid oxygen, close the valve on the oxygen gas cylinder.


Safety Information

  • Oxygen is an oxidizer. It reacts very readily with combustible materials.


  • Liquid nitrogen and liquid oxygen are extremely cold. These materials are capable of causing severe frostbite. Avoid skin contact with these liquids. Also, take care to avoid touching any object which has been in contact with the cold fluids, since it may also be very cold.


  • Dewars are easily broken by mechanical shock or exposure to extreme temperature changes. Take care to avoid striking the Dewar. Don't slam a cold Dewar on a warm countertop, for example.


If you have leftover liquid oxygen, the safest way to dispose of it is to pour it over a noncombustible surface and allow it to evaporate into the air.

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