How do you tell how conductive a particular polymer/metal is? I'm wondering how conductive mercury is in relation to the major stuff like copper and gold. Is indium or gallium fairly conductive? I wanted to try and make a liquid wire, just to see if it works decently. Then I can test to see how well it transmits signals! Wonder if I could make a gaseous wire using (insert gas here)?

I believe they still use mercury switches for the thermostat controls for most people's heater/air conditioning

Conductivity is just the inverse of resistivity...

Gaseous wire?  As in fluorescent lights? A plasma?  Everything "conducts" if you apply enough voltage.  Standing under a tree in a lighting storm or even a foot thick of rubber does nothing to protect you from lighting.  If the electricity can go through air, it'll rip through everything else.

Can you pass electricity through a vacuum?

Oh thats definantly true, I would have a bad day then. The reason I thought of mercury is because I could have a relatively flexbile tube filled with a ton of the stuff, and with such a thick "wire" it should hold amperage a lot better than a tiny copper wire. Or even a car's starter cable.

I think I would much happier using the gallium/indium combo  

I had a buddy with almost a quart of mercury laying around his basement from waaaay back in the day. That stuff IS really heavy! Is the gallium/indium combo more or less conductive than mercury? If its close enough, then that would be the way to go.

It is my impression that mercury switches are passe for HVAC applications. I tried to buy one from an electrical supplier and was told that they are not used anymore (possibly illegal). On the other hand fluorescent lights use argon and mercury vapor to create ultraviolet light, which is converted into visible light using phosphor coating.

That's true, but the amount of mercury vapor inside the bulb is incredibly low.  With just about all gas-discharge tubes, the effectiveness of the tube depends on the concentration of the gas inside.  If you have too much gas, the light it gives off will be fairly weak as the resistance will be quite high.  (That's why my Xenon gas tube isn't as bright as my other tubes.  I suspect that the gas pressure inside is a smidgen too high).  So if you compare the amount of mercury in a mercury switch as opposed to a fluorescent light bulb, you'll see that the switch has a helluva lot more mercury in it.  

Well I do know that both gallium and indium are considered non-toxic substances.  Gallium may require special shipping depending on how much is being transported since it can dissolve other metals when in the liquid state.  (It tends to amalgamate everything kind of like mercury in that regard).  

Yes, you can pass electricity through a vacuum.  TV's, or fancy cathode ray tubes, are supposed to have vacuums inside, so that the path of electrons can be clear for them to run a path onto the phosphor screen.  Beams of electrons existant in vacuum are very important for a great number of things.