[theThinker (OP)]

If I apply a DC 5V voltage across a narrow column of mercury 1cm x 1cm x 0.5m, the current is about 1000 A. How can such an experiment be done at home. Our home supply cannot allow drawing such large a current; the power supply will trip. 

[Bored chemist]

How can such an experiment be done at home.

It can't.
or, at least, it shouldn't be.

[alancalverd]

5kW is not a lot for a cooker circuit, but it's still a hefty transformer and rectifier.

What is the experiment intended to demonstrate?

[Bored chemist]

50 ml of Hg.
About 375 grams.
Heat capacity is about 0.14 J/g K
So it takes about 95 J to heat the mercury by 1 degree C
And at 5 KW the rate of change of temperature will be about 50 degreed per second.
So it will boil after about 7 seconds.

I realise there's a few simplifications in there but I think the point is valid.

[theThinker (OP)]

50 ml of Hg.
About 375 grams.
Heat capacity is about 0.14 J/g K
So it takes about 95 J to heat the mercury by 1 degree C
And at 5 KW the rate of change of temperature will be about 50 degreed per second.
So it will boil after about 7 seconds.

I realise there's a few simplifications in there but I think the point is valid.

I think I can trust your estimate!

[Bored chemist]

OK, so... assuming you were not planning to poison a small town, wheat were you hoping to do?

[evan_au]

If you want to put a lot of current through metal (such as happens during aluminium smelting, for example), you use a low voltage, much lower than 5 Volts - and very thick wires.
https://en.wikipedia.org/wiki/Hall%E2%80%93H%C3%A9roult_process

Note that mercury is volatile, and the invisible fumes are toxic, so you should not have mercury in your home (except, perhaps, sealed in an old-fashioned thermometer); in the lab, it should be kept in a fume cupboard when uncapped.

[Bored chemist]

you use a low voltage, much lower than 5 Volts

Aluminium smelting uses a fairly low voltage, but not much less than 5V

[theThinker (OP)]

This is reported in Peter Graneau in their "Newtonian Electrodynamics". The experiment (1994) was done at MIT to show Ampere longitudinal forces in conductor. They expected mercury to flow due to current. They make a 1/2 inch x 1/2 inch groove in a plastic board for a narrow trough to hold mercury. Between the mercury were two copper rod electrodes for passing currents of 300 - 1000A. If the copper was about 1 cm apart with 1000A, the mercury would be expelled upward. I was wondering how they could pass such high currents in mercury.     

When I was a teenager decades ago, I happen to have a little bead of mercury, don't remember how I got it. It was not the internet age and we know little about mercury poisoning. Played with the bead on my palm and added talcum powder.

I would take the advice here with lumps of salt! I remember a report/video about how a lady - a real expert researcher - was poison by some mercury compound that got through her protective gloves. She died weeks/months later.     

[Eternal Student]

Hi.

I would take the advice here with lumps of salt!

   No, please don't.
   Mercury is extremely dangerous.   There are regulations in place in most countries concerning the use and handling of mercury.   
    You wouldn't take a rock into a busy street and throw it a random direction under the assumption that it probably won't hit anyone, even if it usually doesn't.   Similarly you must not expose yourself, others who live in close proximity with you, or the pregnant lady who comes to your door delivering a package  to mercury vapour by heating the stuff in the way you have suggested.

Thank you and Best Wishes.     

[evan_au]

Ampere longitudinal forces in conductor

This video shows a fountain created by passing electricity through an alloy of Sodium and Potassium (NaK).
It is a demonstrator for the type of coolant planned for some Fast Breeder reactors.

As I recall, they point out that the success of this fountain is largely due to the low density of NaK. If you tried to do it with Mercury, the high density of Mercury would make for a rather disappointing display.

PS: NaK should not be kept in your home. It reacts with moisture or oxygen in the air, and most other things with which it comes into contact, including humans...

[theThinker (OP)]

Hi.

I would take the advice here with lumps of salt!

   No, please don't.
   Mercury is extremely dangerous.   There are regulations in place in most countries concerning the use and handling of mercury.   
    You wouldn't take a rock into a busy street and throw it a random direction under the assumption that it probably won't hit anyone, even if it usually doesn't.   Similarly you must not expose yourself, others who live in close proximity with you, or the pregnant lady who comes to your door delivering a package  to mercury vapour by heating the stuff in the way you have suggested.

Thank you and Best Wishes.     

My Bad! English is not my mother tongue. I mean I would take the advice very seriously

[paul cotter]

That lady spilled a drop of dimethylmercury on her glove, I can't remember her name offhand. The alkyl derivatives of mercury are considerably more toxic than mercury salts and way more toxic than metallic mercury in the liquid state. Many years ago I had business dealings with a neon display manufacturer and there were globules of mercury all over the workshop-the worst part of the scenario was that the owner's daughter was working out on the workshop floor and she was visibly pregnant! I don't know if there were consequences.

[alancalverd]

The reason mercury was so useful in barometers stems from its low vapor pressure at room temperature, allowing it to be used also in diffusion pumps if silicones and organics are undesirable. The incidence of mercury poisoning from the pure metal is very sporadic: there are films of workers in a mercury production plant walking on the surface of vats of the stuff, yet some people succumb to its neurotoxicity at extraordinarily low concentrations.

Nevertheless the MIT experiment was about 40 years behind the times. The electrodynamic railgun was proposed as a satellite launcher in the 1960s and you can make a satisfyingly dangerous model that propels ball bearings  along two parallel rails. IIRC we used 500 microfarad capacitors charged to 300V to deliver a good whack of pulsed current through the 5 mm ball. Apart from the risks of electrocution and an occasional broken window, the college authorities found it quite amusing.

[Rodneyhhernandez]

I don't think that's possible, but it's also perilous. I don't recommend you do something like this, and you can search on youtube. Many videos on youtube explain this.

[alancalverd]

Just as well the US Navy (nor Roscosmos, in the early days) don't watch Youtube.

science.howstuffworks.com/rail-gun1.htm

[vhfpmr]

If you're trying to drive the mercury along the length of the groove in the plastic, with copper electrodes 1cm apart at either side of the groove as you describe, then:

The resistance of the mercury will be 19μΩ, not 4.8mΩ;
the voltage required to drive 1kA will be 19mV, not 4.8V;
the power will be 19W, not 4.8kW;
and the temperature of the mercury will rise at 0.2°/s, not 51°/s.

I'll leave someone else to calculate how many seconds it takes to eject the mercury.

[Bored chemist]

The reason mercury was so useful in barometers stems from its low vapor pressure at room temperature

And there was me thinking it was the density..
Presumably all the ten metre high barometers full of water  somehow escaped my attention.
The water vapour pressure is a complication, but you could allow for it.

[paul cotter]

On the density, you have a slight error in your calculations. You said 50ml of mercury weighs 375g. I'm sure you meant 675g as the density is circa 13.5.

[alancalverd]

The reason mercury was so useful in barometers stems from its low vapor pressure at room temperature

And there was me thinking it was the density..
Presumably all the ten metre high barometers full of water  somehow escaped my attention.
The water vapour pressure is a complication, but you could allow for it.

If you had a liquid of similar density but high vapor pressure, the barometer would be more sensitive to temperature. Not a problem for a laboratory instrument where you can apply any number of corrections but an additional complication at sea.