The Triple Point of Argon and Oxygen

The triple point temperatures ( T tp ) of argon and oxygen were realized by a calorimetric technique with an accuracy of ±0·15 mK. Their values lie within 0.5 mK of the most recent determinations carried out in other laboratories. Errors in T tp due to the cryostat and to impurities were extensively investigated. After initial conditioning, the gases were sealed into triple point cells, in which T tp was stable at the quoted accuracy over a two-year period. The triple point pressure of oxygen was found to be 146.2 5 ± 0.4 Pa. An extensive bibliography of solid-solid equilibria of mixtures with Ar and O 2 is also given.