# Metals rated for conductivity of electricity and heat

Sodium continues to be used in Poppet valves.

Mercury has been used previously.

What material is that pot made of? And how is it (that material and the pot) manufactured? And what were the answers to these questions in Bessemer’s day?

The pot is a steel frame lined with refractory brick and mortor.

The pot is made of carbon steel - lined with refractory/ bricks. The pot can be tilted to pour out the molten metal.

Its a simple vessel. It is lined with the refractory much like a house is built with brick and mortar. (castable refractory is almost the same consistency as mortar

The answers to your questions were pretty much the same in Bessemer’s day too. One of the oldest books on refractory was written in 1556 cite. But mankind has known about refractory since the iron age. The science was not there to known refractory structure in detail (or compositions, or what made a good refractory when the slag was acidic…) but they knew enough.

Si Amigo beat me to it.

What I’d like to know is how well mercury conducts electricity in common mercury switches–according to the Wikipedia data it has about the same conductivity as iron. Asimov wrote that an aluminum wire three times as thick as a copper wire of the same length would conduct electricity just as well–and be considerably cheaper (for long distance transmission of electricity). Does mercury’s liquid state give it an advantage over iron, insofar as conductivity of electricity is concerned?

Mercury is only like iron is you consider 1x10[sup]-7[/sup] Ohm . m (Fe) to be like 9.8x10[sup]-7[/sup] Ohm . m (Hg). In other words iron is a better conductor than mercury.

Resistance, aside from being futile, is typically built out as follows
R = p*l/A
R = Resistance
p = resistivity
l = length
A = cross sectional area

If you want to compare materials of equal length (say in house wiring) then R[sub]1[/sub]/R[sub]2[/sub] = p[sub]1[/sub]*A[sub]2[/sub]/p[sub]2[/sub]*A[sub]1[/sub]

For Al vs. Cu with resistances being equal I get the cross sectional area of the aluminium needing to be ~1.6 that of the copper wire.

Mercury is used in switches and relays not for its great conductivity but because it is a liquid conductor and gives the following benefits :

1> Low current situations : “… the mercury reduces the contact resistance and associated voltage drop, for low-current signals where surface contamination may make for a poor contactfrom Mercury Wetted Relay

2> Contact Erosion : This is the erosion of the contacts because of the plasma (spark) that is created when you turn the switch on or off. “They are used where contact erosion would be a problem for conventional relay contacts. Owing to environmental considerations about significant amount of mercury used and modern alternatives, they are now comparatively uncommon.from Mercury Relay

3> Contact Bounce : This wikipedia articleexplains it very well.

Oh yes it is. If tungsten had high conductivity we’d be running our incandescent lamps off 1 Volt, 100 Amp supplies. Which would be inconvenient, to put it mildly. Just think what house wiring would be like, and the light switches…

That’s just an engineering/manufacturing problem. The filaments would need to get thinner, longer, and coiled more tightly, but it wouldn’t prevent lamp operation on standard house voltage/current. Tungsten’s resistance is only about 3x that of copper, so it can’t get that much more conductive…

of a flourescent bulb, not present in incandesent.

Yeah, that’s what chronos was talking about. Pay attention!