h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hi

I'm trying to make a simple invention and I need to know what liquids will conduct electricity. I need a liquid that will conduct electricity when there is half a medicine cup of the liquid (image: http://images.allegrocentral.com/43/26/Calibrated-Plastic-Medicine-Cup-1oz-176356-PRODUCT-MEDIUM_IMAGE.jpg ) and also, ideally, a full cup of liquid.

My knowledge of science is limited in this area, but here are - what I believe to be - my conditions:

1) The liquid can't be poisonous.
2) The liquid must not undergo chemical change when voltage is applied.
3) The voltage used must be battery-powered: between 1.5 and 9v.

Thanks

Point 2 is going to be your stumbling block, I fancy. All ionic solutions will conduct electricity, but in doing so they will necessarily undergo chemical change. You'd basically need a method of topping up every now and then.

B

Perhaps it might help if I outline my idea:


I want it to be a cube. Each face of the cube has a lightbulb attached (or LED, not sure yet) of a different colour. When you change the cube's position so that (for example) the red bulb/LED is facing up, the red bulb comes on. When you change the cube's position so a different side is up, a different coloured bulb comes on etc.

How it would work:

(In the case of the red bulb) the electrodes (Not sure of terminology there, terminals, + and - wires, or whatever) for the red bulb's circuit are on the opposite face of the cube and inside the cube, so that when the liquid touches the electrodes they form a switch and the red bulb comes on.

(Further note: I have an alarm clock that has this very feature but I assume that this is done by electrical circuitry, which is not an option. It must be done by a liquid)

Thanks for getting back, MB.

If, for argument's sake, I say that condition 2 could be dropped and I can replace the liquid on a daily basis, what would my options be then?

Damn near anything. Salt solution would work just fine.

But I don't see the need for a liquid at all. All you need is a self righting gyro (such as is found in a ship's compass, and can be made for a couple of quid), which will connect the electrodes for you.

Using an ionic liquid as I suggested would not be good at all, because the aforementioned chemical changes would lead to build-up on your electrodes.

B

Easiest and cheapest? Salty water isn't bad. Certainly you could get enough through to light an LED.

Though if you stick with the second condition Mercury might work, though there are all the risks involved with working with mercury.

Self-righting gyro I will look into.

Not sure what I've been doing wrong; I tried it with salt water (varied the amount of salt in tap water and also vinegar (only a thimbleful of vinegar with a 9volt battery and torch-bulb) but the bulb didn't come on.

Well, that's another problem. Whatever liquid you use is going to have a much higher resistance than a length of wire. Plus, if it gets anywhere it shouldn't, it'll probably short-circuit your power source.

B

You're much better doing it with Reed switches and faking it so that it looks as if the liquid is doing it. Liquids do not conduct electricity easily. You'll need electronic circuitry to amplify the tiny current that flows through them.

The only liquid that really conducts electricity at room temperature is mercury, because it is a metal, but it is toxic.

ped

its the vapour of murcury thats toxic

Oops, it's not Reed switches I mean, it is mercury tilt switches.

They in fact operate by the principle you describe, with a liquid (mercury) flowing around inside to make contact in certain orientations. But the mercury is all hidden away so that you can't see it and it is safe.

Taff - you sure?

Mercury can contaminate food (like fish) and then be ingested and lead to poisoning. That's not vapour.

The vapour of elemental mercury is I'm sure what he meant.

In fact elemental mercury isn't really that poisonous at all. What *is* poisonous is mercury salts and they are *really* poisonous. What makes mercury vapour poisonous is that some of it gets oxidised, thereby forming salts and hey presto, nasty nasty stuff.

Ah!

thats why millners(hatters) went mad, they shined top hats with liquid mercury and the fumes eventually drove them bonkers

Not actually bonkers. The twitchiness was caused by mercury poisoning, but it was a physical, rather than mental, result.

Having said that, there can be mental health effects from playing with Mercury too.

You can float a cast iron cannonball in it if you get enough though, which is really if you ever get to see it.

I'm going to see if that's on youtube.

here

http://www.youtube.com/watch?v=Rm5D47nG9k4

amazing!?!?

You can also float lighthouse light and lens assemblies on Mercury...

http://www.trinityhouse.co.uk/interactive/gallery/lynmouth_foreland.html

t.