In thermodynamics, a critical point (or critical state) is the end point of a phase equilibrium curve. The most prominent example is the liquid–vapor critical point, the end point of the pressure–temperature curve that designates conditions under which a liquid and its vapor can coexist. At higher temperatures, the gas cannot be liquefied by pressure alone. At the critical point, defined by a critical temperature Tc and a critical pressure pc, phase boundaries vanish. Other examples include the liquid–liquid critical points in mixtures, and the ferromagnet-paramagnet transition in the absence of an external magnetic field. https://en.wikipedia.org/wiki/Critical_point_(thermodynamics)
Schauberger
(2) "A process for the liquefaction of gases by the Joule–Thomson effect. In this process devised by Carl von Linde (1842-1934) for liquefying air, the air is freed of carbon dioxide and water and compressed to 150 atmospheres. The compressed gas is passed through a copper coil to an expansion nozzle within a Dewar flask. The emerging air is cooled by the Joule–Thomson effect as it expands and then passes back within a second copper coil that surrounds the first coil. Thus the expanded gas cools the incoming gas in a process that is said to be regenerative. Eventually the air is reduced to its critical temperature and, at the pressure of 150 atmospheres (well above its critical pressure), liquefies. The process is used for other gases, especially hydrogen and helium. Hydrogen has first to be cooled below its inversion temperature (see Joule–Thomson effect) using liquid air; helium has first to be cooled below its inversion temperature using liquid hydrogen." [Collins Dictionary of Science. Oxford University Press, Great Britain, 1984, ISBN 0-19-211593-6.] — Ed [The Energy Evolution - Harnessing Free Energy from Nature, The Liquefaction of Coal by Means of Cold Flows]
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