FACT:
from CRC Handbook of Chemistry and Physics and other sources.
Nitrogen:
boiling point at atmospheric pressure:
-195.9 C about -320.6 F [temp of liquid until all boils off]
melting point at atmosperic pressure:
-209.9 C about -345.3 F [temp of slush until all becomes liquid]
F = 9/5(C) + 32
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OBSERVATION:
Unless in an expanding jet, or contained in an evacuated or pressurized vessel, liquid nitrogen can be expected to be between about -320 F and -345 F.
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OPINION:
-396 F??? no idea where that comes from...
(the mistake of subtracting instead of adding the 32 doesn't provide it)
The only thing I can imagine is that a violently venting/expanding/evaporating stream of liquid nitrogen in a jet might cool to this temperature through the Joule-Thomson effect. This effect is what makes the stream projected from an aerosol can cold. One can produce dry-ice from a room-temperature cylinder of pressurized carbon dioxide using simple implements designed for the purpose. The process "wastes" a lot of gas.
So, unless one pumps l-N2 through a nozzel or something, this low temperature isn't attainable. I imagine it might be some sort of "worst-possible case" safety warning requirement in case of accidents.
If anyone knows where this -396 F number comes from, I'd be interested to hear.
Hope this helps.
