An interesting question occurred to me today: When you leave a Dewar flask of liquid nitrogen open to the atmosphere, such as when you're using it to cool the trap of a Schlenk apparatus, oxygen will condense in it since the boiling point of oxygen is 90 kelvins vs 77 K for LN. How fast this happens will depend on the air-exchange into the flask, so if it=E2=80™s covered loosely, presumably the dynamics will slow down. Eventually, though, the flask contains liquid air, not liquid nitrogen, which could become excessively exciting for someone who empties the flask by dumping it out somewhere near something combustible.

I've not seen any data, though, on how fast this actually happens. Has anyone ever seen data on this? If you have, please let me know. It would be useful to know how long one can really leave an open Dewar sitting around.

Regards,

Dan Kuespert

Laboratory Safety Advocate

Johns Hopkins University

Daniel Reid Kuespert, PhD, CSP

dankuespert**At_Symbol_Here**me.com

11101 Wood Elves Way

Columbia, MD 21044

410-992-9709

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