Am Donnerstag, 5. März 2020 22:56:38 UTC+1 schrieb James Waldby:
On Thu, 05 Mar 2020 08:39:26 -0800, pyotr filipivich wrote:
James Waldby ... on Thu, 5 Mar 2020 07:54:24 -0000 ...:
On Wed, 04 Mar 2020 16:26:06 -0500, Jim Wilkins wrote:
"Christopher Tidy" wrote ...
Does anyone here have experience of getting the air out of a mercury
barometer column? My barometer looks like this:
http://www.messcom.de/MESSCOM/MDO/pd...0Bedienanl.pdf

I had wondered about putting the whole barometer in a vacuum
chamber, but I'm not sure if this will work. Unfortunately there's
nowhere to connect a vacuum pump at the top of the column.

Is there anyone with experience here who can give me some tips? So
far, I've been trying to avoid taking the barometer apart in case I
lose the precious (and slightly dangerous) mercury.

The amount of air inside is enough to change the reading by 10 to 20
mm.
...
My German isn't quite good enough to fully translate section 5,
Wartung.

Same here ... however, copy/paste into Google Translate gives ok
results: "5. Maintenance \ Because of the unhindered air access,
the mercury level in the lower vessel oxidizes over time. If the
oxidation has progressed so far that the tip of the scale can no
longer be reliably adjusted to the lower mercury level, the
mercury in the vessel should be removed from the barometer and
cleaned. \ CAUTION! \ The mercury may only be cleaned by
qualified specialist personnel."

That is boilerplate to protect the company. "As Everybody knows"
touching mercury results in your instantaneous poisoning, tremors,
brain damage, and voting to leave the Glorious EU.

It could well be legalistic boilerplate. However, I think there are
two issues with air in the barometer. Section 3 (which got snipped)
is about trapped bubbles of air. Section 5 is about oxidized mercury,
which apparently is fairly toxic.[1]
[1] https://en.wikipedia.org/wiki/Mercury(II)_oxide#Health_issues

Pulling a vacuum on the mix of mercury and mercury oxide - if that's
what's in the barometer and causing problems - wouldn't remove the HgO,
I think. HgO is about 2/3 as dense as Hg so would expand the volume
when present. Christopher, is that consistent with the symptoms?

There's a little oxide in there, but the main problem is that the barometer lay flat for years and was shaken around during a move.

Chris