Quite right, Peter.

Water weighs in at 18 grams/mole. Air is ~20% oxygen (32
grams/mole) and 80% nitrogen (28 grams/mole), for an average of about 28.8
grams/mole. A mole of water vapor takes up about the same volume as a mole
of nitrogen, air, or nitrogen/air mix (very approximately- I'm sure
someone will shout out the Van der Waals equation here). As a result,
water vapor is prone to escape.

I once had a senior research chemist (synthetic organic and
inorganic stuff- nobody here would recognize the name, but EVERYONE is
familiar with his work) point out to me in the lab that when washing
flasks, once the remaining water has drained, flasks actually dry faster
when not on the rack, as water vapor escapes faster when right-side up.

For humidity trays, however, any such influences are rapidly
diluted by any air movement, and little benefit is achieved on the local
scale.

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-AJHicks
Chandler, AZ