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Liquid nitrogen is nitrogen in a liquid state at an extremely low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colorless clear liquid with density of 0.807 g/ml at its boiling point and a dielectric constant of 1.43. Liquid nitrogen is often referred to by the abbreviation, LN2 or "LIN" or "LN" and has the UN number 1977. Liquid nitrogen is a diatomic liquid meaning the diatomic character of the covalent N bonding in N2 gas is retained even after liquefaction. At atmospheric pressure, liquid nitrogen boils at and is a cryogenic fluid that can cause rapid freezing on contact with living tissue. When appropriately insulated from ambient heat, liquid nitrogen can be stored and transported, for example in vacuum flasks. Here, the very low temperature is held constant at 77 K by slow boiling of the liquid, resulting in the evolution of nitrogen gas. Depending on the size and design, the holding time of vacuum flasks (Dewars) ranges from a few hours to a few weeks. The development of pressurised super-insulated vacuum vessels has enabled liquefied nitrogen to be stored and transported over longer time periods with losses reduced to 2% per day or less.〔(DATA BOOK for Cryogenic Gases and Equipment ). aspenycap.org〕 Liquid nitrogen can easily be converted to a solid by placing it in a vacuum chamber pumped by a rotary vacuum pump. Liquid nitrogen freezes at . Despite its reputation, liquid nitrogen's efficiency as a coolant is limited by the fact that it boils immediately on contact with a warmer object, enveloping the object in insulating nitrogen gas. This effect, known as the Leidenfrost effect, applies to any liquid in contact with an object significantly hotter than its boiling point. More rapid cooling may be obtained by plunging an object into a slush of liquid and solid nitrogen rather than liquid nitrogen alone. Nitrogen was first liquefied at the Jagiellonian University on 15 April 1883 by Polish physicists, Zygmunt Wróblewski and Karol Olszewski. ==Uses== Liquid nitrogen is a compact and readily transported source of nitrogen gas, as it does not require pressurization. Further, its ability to maintain temperatures far below the freezing point of water makes it extremely useful in a wide range of applications, primarily as an open-cycle refrigerant, including: *in cryotherapy for removing unsightly or potentially malignant skin lesions such as warts and actinic keratosis *to store cells at low temperature for laboratory work *in cryogenics *in a Cryophorus to demonstrate rapid freezing by evaporation *as a backup nitrogen source in hypoxic air fire prevention systems *as a source of very dry nitrogen gas *for the immersion, freezing, and transportation of food products *for the cryopreservation of blood, reproductive cells (sperm and egg), and other biological samples and materials * *to preserve tissue samples from surgical excisions for future studies *as a method of freezing water and oil pipes in order to work on them in situations where a valve is not available to block fluid flow to the work area, method known as a cryogenic isolation (frequently used in industry and New York district steam pipework) – Electrical heat pumps are now often used for small pipe diameters. *in the process of promession, a way to dispose of the dead *for cryonic preservation in hopes of future reanimation. *to shrink-weld machinery parts together *as a coolant * *for CCD cameras in astronomy * *for a high-temperature superconductor to a temperature sufficient to achieve superconductivity * *for vacuum pump traps and in controlled-evaporation processes in chemistry. * *to increase the sensitivity of infrared homing seeker heads of missiles such as the Strela 3 * *to temporarily shrink mechanical components during machine assembly and allow improved interference fits * *for computers and extreme overclocking * *for simulation of space background in vacuum chamber during spacecraft thermal testing *in food preparation, such as for making ultra-smooth ice cream.〔(Liquid Nitrogen Ice Cream Recipe ), March 7, 2006〕 See also molecular gastronomy. *in container inerting and pressurisation by injecting a controlled amount of liquid nitrogen just prior to sealing or capping.〔(Liquid nitrogen – how to dose effectively ), June 19, 2012〕〔(Chart Dosers Dosing Products ), June 19, 2012〕 *as a cosmetic novelty giving a smoky, bubbling "cauldron effect" to drinks. See liquid nitrogen cocktail. *as an energy storage medium. *branding cattle. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Liquid nitrogen」の詳細全文を読む スポンサード リンク
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