[NewCandle] platinum experiment

[Nick Reiter]

You have no idea how badly I wanted to use "Platinum
Heat" in the subject line...

Anyway, last night on my drive home I recalled that in
the book citation by Colin a while back (Berens and
Singer) the authors had also claimed that they took a
platinum crucible, heated it up, let it cool, and
weighed it, and found that it was slightly lighter
than before, taking many minutes more to return to the
original weight... here is the text:

(p. 383.)
"{...} As already mentioned, a platinum crucible after
having been heated and just allowed to cool, so as to
be no longer sensibly warm to touch, still weighs
less, if immediately placed on the balance, than its
original weight ; and it will often take many minutes
until the balance will again assume it's normal
position. Our explanation of this is that, though cool
to the touch, the molecules are still in a state of
excitation, and hence their lesser weight.."

I have a little slug or irregular ingot of platinum (I
save my old thermocouples:) weighing about 9 grams. 
So this morning, I was experimenting with it - heating
it up with a torch to an orange glow, letting it cool
back to about 25 to 30C and then re-weighing.  Did
this several times.  Negative result.

Now that prompted me to wonder, though, just what
would the influence be on the balance pan if I put the
platinum back on it whilst still orange hot?  I cut
two little squares of non-outgassing alumina felt as
hotpads.  One sat on the balance pan, the other is a
cover piece.  Took a cold weight.  Then I removed the
platinum, heated it up on an insulating block to
orange, and then used stainless tongs to put it back
on the lower pad, on the balance pan.  I left the
cover pad off.  The weight loss was a little over five
milligrams.  Interesting, you can see when the
"chimney" effect kicks in a few seconds after the
balance pan stabilizes, as there will be a secondary
drop of a couple more mg on top of the initial.  As
the Pt cooled, the reading slowly came back up to
original.

I then tried it again, but this time, used the second
cover pad.  I figured this would at least slow the
transfer rate of heat to the air and make for a
different initial weight loss value and a slower
recovery.  It did not - rather it lost the same amount
and followed the same time-weight profile as with no
cover pad.  Thats curious.  Maybe.

More to come.

NR

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