> Ever hear of cold cathodes (not that their cold) but they use
> electrons not ions.
Actually, a "cold cathode" is simply the electrode (not a tube, not a container) that doesn't rely on a hot filament (like a lightbulb.) See article on Wikipedia: [en.wikipedia.org]
> No it does not, the walls of the glass do not get very hot at
> all, if they would they would melt, the gas is usually to
> tenuous for heat transfer further away from the
> discharge/plasma itself (or the Snake :-) )
It sounds as though you might be confusing a plasma with a Geissler Tube (see article: [en.wikipedia.org]) or other gas discharge tubes (see article: [en.wikipedia.org]) -- the latter is insulated, though you may not be aware of it.
> No, you can have a mixture of elements, even normal air
> discharge is possible, depending on pressure, AC/DC, voltage etc.
Plasma is a highly ionized gas, and elements ionize at very specific temperatures (I linked the article on plasmas for you -- another good one is [science.howstuffworks.com] ). A mixture of elements is going to produce very unreliable results. See definition at the Science Dictionary that confirms different elements ionize at different temperatures: [thesciencedictionary.org]
> Again no. Air does not escape from airtight enclosures ie glass
When properly constructed, no. But you do have to be certain that it's airtight. Limestone isn't air tight (it's a very porous stone... pour water on it, and some of the water will sink into the stone) and the seams between granite blocks aren't completely airtight, either.