Editing Refrigerator (section)

===Ultra-low temperature refrigerators===
"Ultra-cold" or "[[ULT freezer|ultra-low temperature (ULT)]]" (typically {{convert|-80 or −86|°C|F|disp=sqbr}}) freezers, as used for storing biological samples, also generally employ two stages of cooling, [[Cascade refrigeration|but in cascade]]. The lower temperature stage uses [[methane]], or a similar gas, as a refrigerant, with its condenser kept at around −40{{nbsp}}°C by a second stage which uses a more conventional refrigerant.

For much lower temperatures, laboratories usually purchase [[liquid nitrogen]] ({{convert|-196|°C|F|disp=sqbr}}), kept in a [[Dewar flask]], into which the samples are suspended. Cryogenic chest freezers can achieve temperatures of down to {{convert|-150|°C|F}}, and may include a liquid nitrogen backup.