Removing mercury from 19th century stick barometer

Diane Fullick <fullick [at] verizon__net> writes

>I am a conservator in private practice and am submitting this query
>for a client who does not have access to the DistList. My client is
>the collections manager for a historic house museum which has a 19th
>century stick barometer mounted on a wall in the museum. One day the
>barometer was removed from the wall and placed flat on the floor and
>some of the mercury spilled onto the floor. An environmental clean
>up agency was called to deal with the spilled mercury, but they
>would not touch the object and only removed the mercury that had
>spilled.
>
>At the request of the director, the collections manager is exploring
>the option of emptying the barometer and disposing of the mercury to
>prevent future spills. ...

I may be wrong but my understanding has always been that whilst one
leg of the U tube is sealed with a vacuum bulb the other has to be
open so that the air  pressure can push the mercury up the vacuum
leg.  If both levels were sealed the mercury would be unaffected by
the air pressure and the barometer would not work. At the risk of
being accused of being politically incorrect, I would also point out
that the area of the mercury exposed to the air is tiny so that the
evaporation rate is negligible. I also seem to recall that the
surface becomes covered with mercuric oxide greatly reducing
evaporation. Is there any evidence mercury barometers have ever
caused any actual harm?  The European  Union is currently trying to
ban mercury barometers and I am rather sad to read suggestions on
the Cons DistList suggesting the removal of the mercury, especially
as people's understanding of them will be lost if they cannot see
the mercury in  the glass.

Simon


                                  ***
                  Conservation DistList Instance 21:25
                 Distributed: Saturday, October 6, 2007
                       Message Id: cdl-21-25-008
                                  ***