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A Dewar tank is a type of vacuum flask that is used to store cryogenic liquids, such as liquid nitrogen. The tank is made of two concentric vessels, with the inner vessel containing the liquid nitrogen. The space between the two vessels is evacuated, which creates a vacuum. The vacuum prevents heat from entering the inner vessel, which helps to keep the liquid nitrogen cold.

Liquid nitrogen is a colorless, odorless liquid at a temperature of −195.8 °C (−320 °F; 77 K). It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a versatile substance with a wide range of uses.

Some of the most common uses of liquid nitrogen include:

• Cryogenics: Liquid nitrogen is used to freeze biological samples, such as cells, tissues, and organs. This allows them to be stored for long periods of time without losing their viability. Liquid nitrogen is also used to cryopreserve embryos and sperm.
• Cooling: Liquid nitrogen is a very effective coolant. It is used to cool electronic components, such as superconductors, and to create fog and smoke effects in theater and film productions.
• Food processing: Liquid nitrogen is used to flash-freeze food, which helps to preserve its flavor and texture. It is also used to make nitrogen ice cream, which is made by mixing liquid nitrogen with cream and sugar.
• Manufacturing: Liquid nitrogen is used in a variety of manufacturing processes, such as welding, metalworking, and plastics processing.
• Medical applications: Liquid nitrogen is used in a number of medical applications, such as cryotherapy, which is used to treat warts and other skin conditions. It is also used to create liquid nitrogen probes, which are used to destroy tumors.

Liquid nitrogen is a powerful substance and can be dangerous if not handled properly. It can cause frostbite and burns, and it can also displace oxygen in the air, which can lead to asphyxiation. It is important to use liquid nitrogen in a well-ventilated area and to wear protective clothing when handling it.

Here are some safety tips for working with liquid nitrogen:

• Always wear gloves, goggles, and a lab coat when handling liquid nitrogen.
• Never touch liquid nitrogen with your bare skin.
• Do not store liquid nitrogen in an unventilated area.
• Be aware of the potential for asphyxiation when working with liquid nitrogen.
• If you spill liquid nitrogen, do not try to clean it up with water. Use dry absorbent material to soak up the liquid.