Matter has three forms; solid, liquid and gas. Every gas can be liquefied and finally solidified if suitable temperature is maintained, so is liquid nitrogen, liquefied form of Nitrogen.
Nitrogen is a chemical element with atomic number 7. It is the most abundant gas in Earth’s atmosphere contributing to 78% of the total volume of the entire atmosphere. Liquid form of this gas is called liquid nitrogen. Due to its abundance in atmosphere and non-toxicity, it is used as a coolant for various purposes including cryosurgery, biological preservation and experimental cooling.
Liquid nitrogen is extremely cold. Its temperature is in the range of 210 degree Celsius (- 346 degree Fahrenheit) to 195.8 degree Celsius (- 320 degree Fahrenheit) below zero. Also, it does not require pressurization and is in dry form, hence it is used widely in cooling.
Due to extreme liquid to gas expansion ratio i.e. 1:694 at Normal Temperature Pressure (NTP), it can generate tremendous force during conversion from liquid to gas. So, it must be contained in a very strong tank and handling should be done carefully. Also, due to its cold temperature, it can cause severe skin burn when comes in contact to skin. So, one should wear insulating gloves while dealing with it.
How Is It Obtained?
Nitrogen is abundant in the air. So, in order to obtain liquid nitrogen, air is cooled and liquefied. Liquefying of air can be done by Siemens cycle or Hampson-Linde cycle, which uses continuous expansion and compression of gas to cool it down. This liquefied air is then subjected to fractional distillation to obtain liquid nitrogen since air is mostly composed of oxygen with boiling point -183 degree Celsius (- 297 degree Fahrenheit) and nitrogen with boiling point -195.8 degree Celsius (- 320 degree Fahrenheit).
Why won’t ice bucket challenge using liquid nitrogen affect the skin?
Although liquid nitrogen is extremely cold, it does not affect our skin when poured rapidly like in ice bucket challenge. This is due to a phenomenon called Leidenfrost effect. This effect is seen when a liquid is poured on a surface which is significantly hotter than the boiling point of liquid. Due to this effect, an insulating layer of a vapor is formed between liquid and surface, hence decreasing the rate of vaporization. The liquid just levitates above the surface in such case.
Let’s consider a splash of liquid nitrogen comes in contact to your arm. Your skin’s temperature is like 32 degree Celsius (89.6 Degree Fahrenheit), while the boiling point of Nitrogen is 195.8 degree Celsius (- 320 degree Fahrenheit). This difference in temperature allows nitrogen vapor to form a layer within the liquid and skin interface, the Leidenfrost effect. This insulating layer now reduces the rate of vaporization of liquid nitrogen. So, the absorption of heat from your skin is low. This keeps your skin cells from dying due to excess heat release.
Hence no damage is done due to splash of liquid nitrogen. But this challenge can also be so lethal that a slight mistake may burn skin severely. Also, you must not take Leidenfrost effect for granted and play with liquid nitrogen. There are various events where it has caused extreme severity in people. It is customary that you wear insulating gloves and use precaution while you are containing it too.