Properties of liquid nitrogen, oxygen, argon and CO₂: reference table

Boiling point, liquid density, gas yield per kilogram and per litre, critical temperature and hazards — the figures engineers look up most often, in one place.

Reference values for the four gases cryogenic systems work with. Gas volumes are given at 15 °C and 1 bar — the same basis used for prices and deliveries in the other blog articles.

Key properties

What follows in practice

• Liquid CO₂ does not exist at atmospheric pressure. Below 5.2 bar it turns into snow or gas, so it is stored only under pressure — about 20 bar at −20 °C.
• The critical temperature of CO₂ is +31 °C. In hot weather a CO₂ cylinder holds a supercritical fluid rather than liquid and gas — hence the limit on the filling ratio.
• A cubic metre of liquid argon weighs almost twice as much as one of liquid nitrogen. Prices per litre cannot be compared across gases — only per kilogram.
• Oxygen is an oxidiser. Oil, grease and combustibles near liquid oxygen can ignite; equipment for it is degreased.

Where these figures are needed

Density and gas yield are the basis of any tank calculation: how many tonnes a vessel holds and how many cubic metres of gas it delivers. Ready tables for tanks of different volumes are in the nitrogen, oxygen and argon tank categories. Price conversion between kilograms, litres and cubic metres is in Price of CO₂, nitrogen and argon.