> Given the properties of plasma, it should be blindingly obvious
> if something contained plasma.
> * since plasma is made up of ions, the container has to be
> completely airtight and the seal between the "lid" and the
> "container" has to be fused shut.
Ever hear of cold cathodes (not that their cold) but they use electrons not ions.
> * there material has to withstand temperatures of several
> thousand degrees Celsius
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 :-) )
> * the plasma has to be made from the gas of a single element
> (like Neon), meaning that the culture has to be capable of
> extracting tons of various PURE elements from different
No, you can have a mixture of elements, even normal air discharge is possible, depending on pressure, AC/DC, voltage etc.
> * Not compounds. One of the elements on the periodic table:
> I haven't seen anyone say what element they thought the
> Egyptians were extracting. The airtightness is another
> problem, too... since ionized gas will escape easily from
> containers that are "airtight" by regular standards.
Again no. Air does not escape from airtight enclosures ie glass tubes.