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Liquid air
Liquid air is air that has been cooled to very low temperatures (cryogenic temperatures), so that it has condensed into a pale blue mobile liquid. To protect it from room temperature, it must be kept in a vacuum insulated flask. Liquid air can absorb heat rapidly and revert to its gaseous state. It is often used for condensing other substances into liquid and/or solidifying them, and as an industrial source of nitrogen, oxygen, argon, and other inert gases through a process called air separation. Liquid air is also replacing liquid nitrogen for theatrical smoke and fog effects.
== Properties ==
Liquid air has a density of approximately 870 kg/m3 (0.87 g/cm3), though the density may vary depending on the elemental composition of the air. Since dry gaseous air contains approximately 78% nitrogen, 21% oxygen, and 1% argon, the density of liquid air at standard composition is calculated by the percentage of the components and their respective liquid densities (see liquid nitrogen and liquid oxygen). Although air contains trace amounts of carbon dioxide (about 0.040%), this gas sublimates (transfers directly between gas and solid, and therefore does not exist as a liquid) at pressures less than 5.1 atmospheres.
The boiling point of liquid air is the same as the lowest of its constituent gases, which is nitrogen; thus air remains liquid below 77 K (-195.79 °C)(-320 F), at standard atmospheric pressure. It can be hard to keep at a stable composition as temperature rises, since the nitrogen will boil off first, leaving the mixture oxygen-rich. This may also occur in some circumstances due to the liquid air condensing oxygen out of the atmosphere.〔Armararego. W. L. F. and Perrin. D. D., Purification of Laboratory Chemicals 4th edition. Reed Educational and Professional Publishing Ltd (1996). p36〕
Liquid air freezes at approximately 58 K (-215 °C)(-355 F), also at standard atmospheric pressure.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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