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Topic: What is a Leyden jar?  (Read 9761 times)

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Corvettaholic

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What is a Leyden jar?
« on: May 06, 2004, 04:29:03 PM »
I've heard that Ben Franklin used things. What exactly is it? Isn't it a big fancy capacitor?

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Re:What is a Leyden jar?
« Reply #1 on: May 06, 2004, 08:09:16 PM »
Its a jar coated inside and out with metal. Since the metal doesn't touch yet its close together it forms a capacitor. Early scientists noticed that when you applied a charge to the capacitor then removed it you could still be shocked.
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Corvettaholic

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Re:What is a Leyden jar?
« Reply #2 on: May 07, 2004, 11:40:51 AM »
Pretty big jar then? I wonder how ancient scientists charged it in the first place, I mean there were exactly power outlets back in the 1800's. When did batteries become widespread? Maybe thats what did it.

I think it was on scitoys.com that I saw gallium & indium for sale in vials. Neat stuff, melts at room temperature. Maybe I could coat a jar in this stuff, then keep it chilly so it sticks? Insta-leyden jar!

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Re:What is a Leyden jar?
« Reply #3 on: May 07, 2004, 01:59:58 PM »
I don’t know if they had batteries then but they used static generators such as the Whimhurst and Van de Graf generators. A cheaper way to make a capacitor is just use bits of wire, aluminum foil used for food and wax paper also used for food. All you have to do is make two plates near each other but not touching, roll the aluminum foil alternating with the wax paper, roll it around a pencil or something: foil-paper-foil-paper. Connect the two pieces of foil to the wires and you have a capacitor. The more surface area the plates have next to each other the more capacitance it has and the more energy you can store. Just be careful, applying high voltage from something like a static generator can build up the amperage into a lethal current. I would suggest using an AA battery for testing it. High current and voltage can electrocute you if it flows through your chest cavity (don’t hold one wire in one hand and the other wire in the other hand).

Scitoys has gallium that melts near room temperature and can be super cooled before it crystallizes, a gallium alloy that is liquid at room temperature, and an indium alloy called Field’s metal that melts in hot water. All three stick to glass and don’t need to be cooled to keep sticking, just melt it and smear it over the glass, it is good for making mirrors too.
« Last Edit: May 07, 2004, 02:05:36 PM by Scratch- »
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Re:What is a Leyden jar?
« Reply #4 on: May 07, 2004, 02:45:22 PM »
The liquid gallium/indium alloys are neat, but they are incredibly messy.  They stick to everything and are a complete mess if you ever spill it.  While Mercury will bead up and is actually fairly easy to clean up, gallium/indium alloys won't bead up and will stain everything.   ;D
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Corvettaholic

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Re:What is a Leyden jar?
« Reply #5 on: May 07, 2004, 03:14:07 PM »
I remember building capacitors back in highschool with aluminum foil tape and business cards. Had about 40 nanofarads of capacitance. As far as making a huge mess with gallium/indium, can't I just cool it back down to a solid once I got it where I want it? I read that article on scitoys, and it gives me plenty of neat ideas. That stuff could be great for homebrewing mirrors for my steam generator. Once you dump this stuff on a surface, cool it till it solidifies, can you polish it or will it all rub off? I suppose the friction may melt it.

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Re:What is a Leyden jar?
« Reply #6 on: May 07, 2004, 03:18:19 PM »
Just rub it on there with some cotton, it will stick whether you want it to or not. You might have to sand it to get it off even if it is liquid.
« Last Edit: May 07, 2004, 03:19:17 PM by Scratch- »
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Offline Mitch

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Re:What is a Leyden jar?
« Reply #7 on: May 07, 2004, 04:11:57 PM »
Gallium has a high efficiency for "wetting" glass, it shouldn't be an issue.
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