[Corvettaholic]

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)?

[Mitch]

mercury should work, it's superconductive at 5K or so.

[gregpawin]

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.

[Corvettaholic]

Let me clarify, gaseous conductor as in able to transmit power from a 9V battery. Other than the health hazards, is there anything I'm overlooking for using a tube filled with mercury as a wire? Figure I stick big thick copper electrodes at each end. The motivating idea behind this is to be able to safely carry a ridiculous amount of amperage. Like over 500 amps.

[Scratch-]

Can you pass electricity through a vacuum?

[jdurg]

One thing you have to remember is that as you increase the amperage going through a wire, the temperature will increase at a fixed rate since the line isn't a 100% perfect conductor.  (I.E. there is some minimal resistance present).  What you don't want is your mercury filled tube increasing in temperature to a point where the tube shatters, thus flinging mercury all over the place.  

[Corvettaholic]

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.

[jdurg]

You also can't forget the fact that the tube will be quite heavy as mercury is a very dense element.  You might be better off using one of the many gallium/indium alloys which are liquid at room temperature, but not nearly as dense as mercury is.  (Nor are they as toxic).

[Corvettaholic]

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.

[billnotgatez]

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.

[jdurg]

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.  

[Corvettaholic]

But there is something to be said about the health factors or mercury. I assume gallium and indium are a lot safer, and easier to transport without getting into federal trouble. I'm assuming the conductivity of the aforementioned metals are all fairly similar?

[jdurg]

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).  

[Corvettaholic]

I was reading up on gallium a little while back, and I saw the pictures of what it did to metal. I guess that kind of rules out pumping it with a metal pump. Do plastic pumps exist that will hold up to pumping this stuff?

[gregpawin]

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.