Re: Ball lightning - Terry's thoughts....

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: William Beaty <billb@xxxxxxxxxx>

On Sat, 13 Aug 2005, Tesla list wrote:

> >It might be interesting to place an adjustable sphere-gap in the oven and
> >see how far a spark would jump. Without having tried this, I'd give a
> >seat-of-pants guess of 1mm or so.
>
> I just tried it, forming a 2 1/2 loop of around 24 guage copper wire
> with around a 1 mm gap.

Very long sparks can jump from sharp points.  To accurately measure
e-fields using air breakdown you have to use sphere terminals with
diameter around 10x larger than the gap setting.  1" brass drawer-pulls
would be good.


> Then again, perhaps its air and not a copper plasma, because it
> wasn't green but white?

Yeah, incandescent air.  If you capture such a plasmoid in an inverted
pyrex cup, it turns pink-violet (resembling the same boron flame color
when doing borosilicate glassblowing.)  In standard soda-glass containers
it turns dimly sodium yellow.  If you use a bit of honey to stick some
salt grains on the glass surface first, the plasmoid flares brilliant
yellow as each grain loosens and falls through the plasma.  I don't have
copper sulphate here or i'd try that.  Or strontium chloride (red?)

Some chemistry instructors use microwave ovens to demonstrate industrial
plasma chemistry. I once tried some sulfur crystals in the inverted cup
with the plasmoid, hoping to duplicate the "sulfur microwave light bulb"
device, but it made clouds of sulfur dioxide or some other acrid gas.
Guess I'll have to try it under argon instead.


> I didn't think the voltage would get high enough. I know its the field
> involved, but under a few hundred volts however sharp you get your
> needle point, you're still not going to get corona, from what I've
> heard.

Most magnetron power supplies are somewhere above 5 kilovolts.  I don't
know what the antenna output voltage might be, but if it's in the low
kilovolts and the hi Q is stepping it up, the fields are already near the
breakdown threshold for air ...which is verified by the outbreaks of
corona coming from sharp torn edges of aluminum foil.   The plasma occurs
reliably with 900 watt ovens, but it harder to trigger with old 500w
ovens.


Here's some weirdness:  about 15 minutes after running a brilliant
microwave argon-gas plasmoid in a 5" round-bottom flask, I noticed that
the flask looked yellow against a white tabletop: aguely the look of
bromine gas.  There was a mashed-kleenex stopper in the flask.  So I blew
into the flask with a plastic soda straw and the yellow vanished.  I
carefully sniffed around and got a strong nose-burn scent, but nothing
recognizable.  Was it something from the bit of aluminum that triggered
the plasma?  Or perhaps air contamination made some oxides of nitrogen?
They're supposedly reddish brown.  But maybe they'd look yellow when
dilute.



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William J. Beaty                            SCIENCE HOBBYIST website
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