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Date:      Tue, 31 Dec 2002 22:41:37 +0000
From:      Matthew Seaman <m.seaman@infracaninophile.co.uk>
To:        freebsd-questions@FreeBSD.ORG
Subject:   Re: Water Damage
Message-ID:  <20021231224137.GA2474@happy-idiot-talk.infracaninophi>
In-Reply-To: <xaisxa2bqq.sxa@localhost.localdomain>
References:  <20021230110818.A91089-100000@cactus.fi.uba.ar> <3E11070B.5000306@jcdurham.com> <3E11E7A3.5070404@mac.com> <xaisxa2bqq.sxa@localhost.localdomain>

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On Tue, Dec 31, 2002 at 12:07:41PM -0800, Gary W. Swearingen wrote:
> 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.

Arrgh.  I'm sorry but this is bugging me.  The word is "miscible",
from the Latin "miscere" to mix.

The point of rinsing with isopropanol is simply to disolve and flush
away as much of the bulk water as possible.  The drips of isopropanol
left on the kit will still contain water (As Chuck pointed out,
it's difficult (read "expensive") to make completely dry isopropanol
and handle it so that it stays dry). Even so, there will be much less
water present after rinsing, so that it won't take much time to dry.
The isopropanol itself being a lot more volatile than water evaporates
fairly quickly.

It's not that mixing alcohol with the water makes the water evaporate
faster.  The rate of evaporation depends on a number of factors ---

    * the partial pressures of the alcohol and water vapours above the
    liquids --- these will be completely independent of each other to
    a good approximation.

    * the concentration of the different components in the bulk liquid.
    Adding alcohol reduces the water concentration so this factor
    would actually tend to lower the rate of evaporation.

    * the surface area of the liquid vapour interface, which adding
    alcohol tends to increase, hence speeding up evaporation.

Are we sufficiently off topic yet?

	Happy New Year,

	Matthew


-- 
Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
                                                      Savill Way
                                                      Marlow
Tel: +44 1628 476614                                  Bucks., SL7 1TH UK

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