RE: Color Fades in discharges

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Original poster: "Steve Conner" <steve.conner@xxxxxxxxxxx>

Hi Mike,

That's a very interesting problem. From the chemistry of the situation, we
know that the only things in air that can get "burned" are nitrogen and
oxygen. The oxygen reacts with the electrode material, so for instance a
copper electrode might get covered in a film of copper oxide and that takes
oxygen out of the air.

Also, the oxygen and nitrogen can react to produce nitrogen oxides, which
react with any water present to produce nitric acid. (The fact that you get
a hydrogen line suggests that there is water vapour present) This takes
nitrogen and oxygen out of the air.

The fact that the nitrogen spectral lines are down by half suggests that at
least half the nitrogen has been fixed. So I guess whatever is glowing grey
in your tube is whatever is left over. I seem to remember that the glow
colour for oxygen is greyish white, but then again, I would expect the
oxygen to get "burned" first.

The fact that "burned" air sustains discharges to a lower voltage is
probably because the air pressure will fall as more gas is converted to
liquid and solid compounds that take up much less space.


Steve C.