reproducible temperatures, that an international calibration standard for thermometers called ITS–90 relies upon triple-point cells of hydrogen, neon, oxygen, argon, mercury, and water for delineating six of its defined temperature points. Table of triple points This table lists the gas–liquid–solid triple points of several substances. Unless otherwise noted, the data come from the U.S. National Bureau of Standards (now NIST, National Institute of Standards and Technology). Notes: For comparison, typical atmospheric pressure is 101.325 kPa (1 atm). Before the new definition of SI units, water's triple point, 273.16 K, was an exact number. See also Critical point (thermodynamics) Gibbs' phase rule References External links Chemical properties Phase transitions Thermodynamics Threshold temperatures Gases 1873 introductions