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Re: Do you know anything about this activity?



Sheron,
I should mention first a practical application of current detection and
amplification in a flame. The ionization detector is used as the most
sensitive available detector of the efflux from a gas chromatograph column
which seperates the volatile components of an input mixture ( of as many as
100 components).
The gas flow carrying this mixture, differentially adsorbed by a column
packing as simple as fuller's earth or some much more expensive concoction,
passes finally out of a flame pipe where a charged wire is suspended. The
varying flow of ions is easily amplified to a current suited to computer
processing or graphing. Traces as small as 1 part per trillion ( 1E-12) are
detected.

A gas pipe connected to a bunsen via a box with an elastic diaphragm provides
a flame modulated in amplitude by sound vibrating the box. An ion generator
and a pair of detector electrodes strategically placed in the flame will
register a varying current at high impedance.

Duddell ( 1900) originated the singing arc. It is a variation of this
device that your interlocutor has in mind:
A series tuned circuit is connected across a DC arc. If the tuned
circuit's frequency is suitable, the arc will emit a tone of that frequency.
In the same way, sound impinging on a DC arc can control the current
though a transformer connected across the carbon electrodes, the other
winding of which is connected to an ( old-style) telephone earpiece.

Substituting a flame with available ions for the carbon arc, you will see that
the wires hanging into the flame were the 'high-tension' side of an old
style radio output transformer. ( These have vanished from use, so a
current replacement would be a step down audio transformer feeding a moving
coil loudspeaker used as a microphone.) I would recommend connecting one
end of the winding to the metal bunsen, and the other to an electrode
suspended in the flame.

The kind of string needed to provide available ions would be made of asbestos
or a more modern high-temp equivalent.

Starling & Woodall 'Physics' has more on Duddell and related topics.

Brian


At 09:33 10/9/97 +0100, you wrote:
Please help

Thanks in advance.
Sheron Snyder

My name is Eric Arnold, I am a senior in high school, and I'm
taking AP physics. We have to do a semester project on anything physics
related. I asked my dad for an idea and he said that when he was a kid he
made a speaker out of a flame. He couldn't remember all the details, but
thought it involved putting a string soaked in salt water in the flame,
and then putting the ends of a speaker wire in the flame. If you know how
to do this, or have an idea of where to look, who to ask, I would greatly
appreciate it.


Have you ever seen/done/heard about the above project? I don't know what
salt water does to string and why the string would not burn at some point.
Thanks


Sheron Snyder
brian whatcott <inet@intellisys.net>
Altus OK