Liquid Nitrogen Facts

Liquid nitrogen immediately boils into its vapor at room temperature. The fog is a mixture of nitrogen gas and water vapor from the air.
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Liquid nitrogen is nitrogen that is cold enough to exist in liquid form. It is used for many cooling and cryogenic applications. Here are some facts about the liquid form of the element and information about handling it safely.

Liquid Nitrogen Facts

  • Liquid nitrogen is the liquefied form of the element nitrogen that is commercially produced by fractional distillation of liquid air. Like nitrogen gas, it consists of two nitrogen atoms sharing covalent bonds (N2).
  • Sometimes liquid nitrogen is denoted as LN2, LN, or LIN.
  • Liquid nitrogen has the UN number 1977.
  • At normal pressure, liquid nitrogen boils at 77 K (−195.8 C or −320.4 F).
  • The liquid-to-gas expansion ratio of nitrogen is 1:694, which means liquid nitrogen boils to fill a volume with nitrogen gas very quickly.
  • Nitrogen is nontoxic, odorless, and colorless. It is relatively inert. It is not flammable.
  • Nitrogen gas is slightly lighter than air when it reaches room temperature. It is slightly soluble in water.
  • Nitrogen was first liquefied on April 15, 1883, by Polish physicists Zygmunt Wróblewski and Karol Olszewski.
  • Liquid nitrogen is stored in special insulated containers that are vented to prevent pressure buildup. Depending on the design of the Dewar flask, it can be stored for hours or for up to a few weeks.
  • LN2 displays the Leidenfrost effect, which means it boils so rapidly that it surrounds surfaces with an insulating layer of nitrogen gas. This is why spilled nitrogen droplets skitter across a floor.

Liquid Nitrogen Safety

When working with liquid nitrogen, taking safety precautions is paramount:

  • Liquid nitrogen is cold enough to cause severe frostbite upon contact with living tissue. Wear proper safety gear when handling liquid nitrogen to prevent contact or inhalation of the extremely cold vapor. Cover and insulate skin to avoid exposure.
  • Because it boils so rapidly, the phase transition from liquid to gas can generate a lot of pressure very quickly. Do not enclose liquid nitrogen in a sealed container, as this may result in it bursting or an explosion.
  • Adding a lot of nitrogen to the air reduces the relative amount of oxygen. This can result in an asphyxiation risk. Cold nitrogen gas is heavier than air, so the risk is greatest near the ground. Use liquid nitrogen in a well-ventilated area.
  • Liquid nitrogen containers may accumulate oxygen that is condensed from the air. As the nitrogen evaporates, there is a risk of violent oxidation of organic matter.

Liquid Nitrogen Uses

Liquid nitrogen has many uses, mainly based on its cold temperature and low reactivity. Examples of common applications include:

  • The freezing and transporting of food products
  • The cryopreservation of biological samples, such as sperm, eggs, and animal genetic samples
  • Use as a coolant for superconductors, vacuum pumps, and other materials and equipment
  • Use in cryotherapy to remove skin abnormalities
  • The shielding of materials from oxygen exposure
  • The quick freezing of water or pipes to allow work on them when valves aren't available
  • A source of extremely dry nitrogen gas
  • The branding of cattle
  • The molecular gastronomy preparation of unusual foods and beverages
  • The cooling of materials for easier machining or fracturing
  • Science projects, including making liquid nitrogen ice cream, freezing flowers and then watching them shatter when tapped onto a hard surface, and making nitrogen fog