Date: Tue Aug 28 12:06:27 2007

Author: Richard Heckathorn

Subject: Re: Mercury replacement-Can we use it?

Post:
Greetings,

Here in Ohio it is illegal to have any mercury in
the public schools K-12. I also understand that
insurance companies may have something written
into college policies as to its non-use.

I still have a 1-lb of mercury that I use for
density comparison but have not used it in a demo
where it is open to the air.

Dick


Helping teachers who facilitate, motivating
students who learn.
Dick Heckathorn 14665 Pawnee Trail Middleburg
Hts, OH 44130 440-826-0834
web.cvcaroyals.org/~rheckathorn/
Adjunct Physics Teacher - Baldwin Wallace College
Physics is learning how to communicate with ones
environment so that it will talk back.


-----Original Message-----
From: tap-l-owner@lists.ncsu.edu
[mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of
Stan Dodds
Sent: Tuesday, August 28, 2007 10:08 AM
To: tap-l@lists.ncsu.edu
Subject: Re: [tap-l] Mercury replacement

Ionic solutions do conduct, but the conductivity
is likely to be a few
orders of magnitude less than a good metal.
Electrolysis products can
also build up on the electrodes, further
increasing the total
resistance.

Unless you are going to swim in it, metallic
mercury is principally an
inhalation hazard. The vapor pressure is quite
low, however, and you
are unlikely to build up a significant
concentration in a modern,
well-ventilated commercial building, especially if
you keep the exposed
surface area small. As an added precaution, you
can put a small amount
of oil (microns thick, not millimeters) on the
surface to further slow
the evaporation rate. Your safety office probably
has a mercury vapor
monitor you could use to verify that the levels
are safe.

For a more exotic solution, you might try a
gallium-indium-tin eutectic
marketed as Galinstan. (see Wikipedia entry) It
surely conducts well
enough, but apparently wets almost everything,
making it a bit tricky
to use.

Stan


On Aug 27, 2007, at 4:11 PM, David Tam wrote:

> Hi everyone,
>
> I've been working on several demos that require
a pool of mercury as
> part of an electrically conductive path. I'd
like to be able to keep
> doing some of these without the toxic hazard,
i.e. eliminate the
> mercury. I've tried salt water and water with
copper sulfate,
> thinking the salt was all that was needed to
sustain conduction, but
> neither work. Does anybody have a good
solution?
>
> Thanks,
>
> David
>






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