"fog" from a saturated salt solution?

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From: Geoff Ruth (gruth@leadershiphigh.org)
Date: Fri Feb 14 2003 - 22:25:04 PST 

Message-Id: <a05200f0dba738a999b64@[192.168.1.25]>
Date: Fri, 14 Feb 2003 22:25:04 -0800
From: Geoff Ruth <gruth@leadershiphigh.org>
Subject: "fog" from a saturated salt solution?

Today my students and I came across a phenomena that has me
completely baffled. We were looking at solutions and solubilities,
and dumped a bunch of sodium chloride into a beaker of tap water.
Then we put the beaker on a magnetic stirrer and turned it on at a
medium-high setting. I put the whole thing on an overhead projector
turned on, in a darkish room, so students could see it.

After a few moments, whisps of whiteish "fog" or "steam" seemed to be
coming out of the beaker. After travelling for about 5 cm, the "fog"
would dissipate from the beaker. After about 2 minutes of stirring,
the "fog" stopped emanating from the beaker. It was quite noticeable
and surprised the hell out of me.

I have a vague notion this has something to do with salt crystals
providing condensation nuclei in the air for water droplets to adhere
to, but I can't really put this idea into a coherent explanation. Can
anyone help?

- Geoff

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