Liquid nitrogen is very cold! At room temperature and pressure, liquid nitrogen boils into nitrogen gas. It even looks like boiling water, except that it is surrounded by a cloud of water vapor. Here is a look at the temperature of liquid nitrogen, liquid nitrogen facts and uses, and safety information.
How Cold Is Liquid Nitrogen?
The temperature of liquid nitrogen is −195.79 °C (77 K; −320 °F). This is the boiling point of nitrogen. However, nitrogen can exist as a liquid between 63 K and 77.2 K (-346°F and -320.44°F). Below this temperature, nitrogen forms a solid, while above its boiling point, nitrogen exists as a gas.
Liquid Nitrogen Facts
Here are some interesting liquid nitrogen facts:
- Liquid nitrogen is diatomic nitrogen, N2. For this reason, it’s often called LN2.
- Liquid nitrogen is colorless, odorless, flavorless, and non-toxic.
- Liquid nitrogen looks much like boiling water.
- Liquid nitrogen has a low viscosity. In other words, it readily flows.
- Polish physicists Zygmunt Wróblewski and Karol Olszewski were the first to liquefy nitrogen on April 15, 1883.
- Liquid nitrogen is produced by fractional distillation of liquid air.
Liquid Nitrogen Uses
Liquid nitrogen has many uses:
- Science projects, such as demonstrating the Leidenfrost effect, making liquid nitrogen ice cream, making fog, and flash-freezing flowers
- Freezing food for storage and transportation
- Protecting samples from oxygen exposure
- As a source of dry nitrogen gas
- Branding livestock
- Molecular gastronomy
- Cooling materials to make them easier to fracture or machine
- Preserving biological samples
- Cooling superconductors, vacuum pumps, and other equipment
- Cryotherapy, such as wart removal
- Quick-freezing water in pipes for plumbing
- Fire suppression
- Shrink welding
Liquid Nitrogen Risks
Nitrogen isn’t toxic, but liquid nitrogen does pose some health and safety risks. It can cause frostbite, poses an asphyxiation risk, and can cause containers to burst.
- Liquid nitrogen is a cryogenic fluid. So, it can immediately freeze living tissue. But, this risk is somewhat diminished by the Leidenfrost effect. Since liquid nitrogen is a boiling liquid, the droplets are surrounded by insulating vapor. Serious and potentially fatal frostbite typically results from ingesting liquid nitrogen or from extreme spills. Liquid nitrogen ice cream is safe because the nitrogen boils off and is not an ingredient. On the other hand, liquid nitrogen cocktails pose a risk.
- The nitrogen concentration in air increases as the liquid boils into a gas. The cold gas is heavier than air and sinks to the bottom of a room. As the gas warms, it becomes lighter than air and rises. Eventually, nitrogen mixes into air, decreasing the percentage of oxygen. So, the risk of asphyxiation depends on location in a room and whether or not it’s enclosed. Because nitrogen is odorless, colorless, and flavorless, asphyxiation may occur with little or no warning.
- Similarly, as nitrogen boils into a gas, the atmospheric pressure increases significantly. At room temperature, the liquid to gas expansion ratio of nitrogen is 1:694. This isn’t a big deal in a large space, but easily ruptures containers. This is why you use a container called a dewar to store and transport liquid nitrogen and other cryogenic gases. A dewar allows for pressure release. Never store liquid nitrogen in a sealed container.
- Because it’s so cold, liquid nitrogen can liquefy oxygen from air. Oxygen can accumulate around a liquid nitrogen container, leading to oxidation of materials. Organic substances may violently oxidize.
Don’t enclose liquid nitrogen in sealed containers. Wear appropriate clothing and protective gear. Wear long pants and either a lab coat or shirt with long sleeves, insulating gloves, eye protection, and shoes with covered toes. Only work with liquid nitrogen in a well-ventilated area and watch for signs of hypoxia. Asphyxiation causes rapid breathing, fatigue, nausea, faulty judgement, and vomiting. These symptoms can proceed to unconsciousness and death. Liquid nitrogen is a common and useful cryogenic gas, but its storage and use requires caution.
- Almqvist, Ebbe (2003). History of Industrial Gases. Springer. ISBN 0306472775.
- Health & Safety Services, Birkbeck. Liquid Nitrogen – Code of Practice for Handling. University of London.
- Henshaw, D. G.; Hurst, D. G.; Pope, N. K. (1953). “Structure of Liquid Nitrogen, Oxygen, and Argon by Neutron Diffraction”. Physical Review. 92 (5): 1229–1234. doi:10.1103/PhysRev.92.1229
- Wallop, Harry (October 9, 2012). “The dark side of liquid nitrogen cocktails”. The Daily Telegraph. Telegraph Media Group.