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Date:      31 Dec 2002 12:07:41 -0800
From:      swear@attbi.com (Gary W. Swearingen)
To:        Chuck Swiger <cswiger@mac.com>
Cc:        freebsd-questions@FreeBSD.ORG
Subject:   Re: Water Damage
Message-ID:  <xaisxa2bqq.sxa@localhost.localdomain>
In-Reply-To: <3E11E7A3.5070404@mac.com>
References:  <20021230110818.A91089-100000@cactus.fi.uba.ar> <3E11070B.5000306@jcdurham.com> <3E11E7A3.5070404@mac.com>

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Chuck Swiger <cswiger@mac.com> writes:

> Jim Durham wrote:
> [ ... ]
> > That's an excellent idea because the alcohol will "absorb" the water
> > (I believe the correct term is that water is "misable" in alcohol), so
> > when the alcohol evaporates it takes the water with it.

But that "so" there seems unjustified.  Maybe the last part is true, but
does the fact that two liquids are misable mean that the lighter one
will carry off the heavier one in evaporation?  One could as easily
guess that the heavier one keeps the lighter one's evaporation rate down
to the heavier one's -- or anywhere in between.  Or they each evaporate
at their own rates, separating at the moment of evaporation.

> Yes, water and alcohol are misable in any proportions, but there's
> slightly more to it than that.  You cannot get 100% pure alcohol via
> distillation-- this is why isopropyl rubbing alcohol goes up to 91%
> alcohol, and why ethanol like grain only goes up to 195 proof (~98%).

From that I'd guess that alcohol evaporates from a water mixture at or
near it's normaly fast rate, carrying off a small fraction of it's
weight or volume (9%) of water and leaving water behind unless there's
more than about 10 times the alcohol as water.  Just guessing, tho.  Do
the two molocules act like one which evaporates faster than water but
slower than alcohol?  Do they stay together after evaporating?  Wouldn't
that give 50%, not 91%?

My first guess was that the alcohol would leave all of the water behind
in evaporation and that one must flush with enough alcohol to remove the
absorbed water in the form of flushed-away liquid mixture.  I now suspect
the truth is somewhere in between.  I kinda doubt that I could dry up a
half cup of water much faster by mixing in a half cup of alcohol.  But
I guess I can see how a thick layer of alcohol could evaporate away a
bit of dampness.  It's certainly a widespread practice; it must be true.

Anybody know for sure how this works (especially in the cup example)?

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