Leiden scale

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The Leyden temperature scale could plausibly have been introduced around 1894, when Heike Kamerlingh Onnes' cryogenic laboratory was established in Leyden, Netherlands. The symbol is probably °L.

The scale is supposed to be the kelvin scale shifted so that the boiling points of hydrogen and oxygen become zero and 70 respectively. As it turns out, oxygen under a standard atmosphere boils at a temperature in the 90.15 to 90.18 K range. For hydrogen, it depends on the molecular variety. The boiling point is 20.390 K for "normal" hydrogen (made up of 75% orthohydrogen and 25% parahydrogen) and 20.268 K for pure parahydrogen. If one supposes that absolute zero is at -20.15 °L, the purported definition is satisfied and, as a bonus, the shift between the Leyden, Kelvin and Celsius scales is a whole number in each case.