This is an effect described with regards to the anesthetic gas ENTONOX
ENTONOX is a 50:50 mixture of gaseous oxygen and nitrous oxide
If the cylinder is stored below -6 degree (the pseudocritical temperature of ENTONOX) Celsius, the nitrous oxide component can separate as a liquid (lamination)
This can lead the delivery of uneven mixtures, too much oxygen at the beginning and too much N2O at the end of the cylinder life
Danger of lamination can be avoided by immersing the cylinder in water at 52 degree Celsius and inverting it 3 times, or by keeping it above a temperature of 10 degree Celsius for 2 hours before use.
Other methods are keeping the cylinder horizontal, at a temperature of 5 degrees or more for more than 24 hours OR by connecting a tube from the valve housing at the top to a point near the bottom which prevents the withdrawal of pure nitrous oxide
N.B. The critical temperature of a gas is the maximum temperature at which compression can cause liquefaction. Mixing gases may change their critical temperature. The Poynting effect produces a 50:50 mixture which reduces the crtical temperature of N20 (Critical temperature is 36.5 degree Celsius); so Entonox has a pseudocritical temperature of -6 degree Celsius
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