What are the physics of a water (or salt water) Leyden jar?

Discussion in 'Physics' started by Ele1, Dec 3, 2014.

  1. Ele1

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    The Leyden jar with foil on the inside and outside of the jar appears to have a more standard capacitor construction. If the outer and inner foil are connected to a battery as in a standard capacitor, would this type of Leyden jar charge?

    The water (or salt water) Leyden jar seems very different. What are the physics of this type of Leyden jar? Are the charges stored on the surface of the inside conductor in a double layer? Why does the high voltage not break down the water? Could a battery charge this type of Leyden jar?
     
  2. studiot

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  3. Ele1

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    The above thread reference discusses the Leyden jar with foil on the inside and outside of the jar.

    The salt water Leyden jar has a charged inner conductor immersed in salt water. A conductor with an excess charge in contact with an electrolytic solution should form a double layer. A double layer should confine the electric field to atomic distances.

    If the excess charge on the inner conductor is in a double layer then how does the electric field reach the conductor on the outside of the jar?

    If the excess charge on the inner conductor is not in a double layer then what is (could be) happening?

    The water Leyden jar was the first experimental capacitor, yet I could not find any literature on the physics of the stored charge on the inner conductor immersed in salt water.
     
  4. studiot

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    Somewhere in that my linked thread was a post by a Dutch member (Leyden was Dutch) that referred to the Dutch museum where the original documents/equipment etc are.

    I haven't studied the history of the jar that deeply, but perhaps if you can give more detail we can work out an answer.

    Do you have a reference and a diagram?
     
  5. BR-549

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    What is this mysterious double layer?
    What makes you think that a electric field is ever limited to atomic distances?

    In a salt water jar, the salt water is the inner plate and holds the charge. Not the conductor.
     
  6. alfacliff

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    tesla used salt water imersed jars to handle more power in his colorado springs system, the water carried off heat better than foil. this would not be a problem with a dc or battery supply, only rf.,
     
  7. Ele1

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    BR-549, the double layer interfacial:
    http://en.wikipedia.org/wiki/Double_layer_(interfacial)

    I think you are saying the excess charges are inbetween the salt water and the inside surface of the jar and not between the inner conductor surface and salt water.

    The inner conductor is suspended in the salt water and not in close contact with the inner surface. Even in close contact, a thin atomic layer of electroltye should hold the excess charges and confine the electric field (according to theory).

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    studiot,
    http://en.wikipedia.org/wiki/Leyden_jar
    The original form of the device was just a glass bottle partially filled with water, with a metal wire passing through a cork closing it. The role of the outer plate was provided by the hand of the experimenter. Soon it was found that it was better to coat the exterior of the jar with metal foil (Watson, 1746), leaving the (accidentally) impure water inside acting as a conductor, connected by a chain or wire to an external terminal, a sphere to avoid losses by corona discharge. Later the water inside was replaced with a second metal foil lining.
     
  8. BR-549

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    Your link is dead. I have never heard of a double layer. Double layer of what?

    Again.......the salt water replaces the inner conductor( of regular Leyden jar).........the water becomes the inner plate.

    What is it about this that you don't understand?

    Do you understand how a capacitor works?
     
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  9. Ele1

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    From:
    http://www.gutenberg.org/files/22766/22766-h/22766-h.htm#p32

    Leyden Jar.—This is shown in Fig. 18. The jar (A) is of glass coated exteriorly at its lower end with tinfoil (B), which extends up a little more than halfway from the bottom. This jar has a wooden cover or top (C), provided centrally with a hole (D). The jar is designed to receive within it a tripod and standard (E) of lead. Within this lead standard is fitted a metal rod (F), which projects upwardly through the hole (D), its upper end having thereon a terminal knob (G). A sliding cork (H) on the rod (F) serves as a means to close the jar when not in use. When in use this cork is raised so the rod may not come into contact, electrically, with the cover (C).
    The jar is half filled with sulphuric acid (I)

    http://www.gutenberg.org/files/22766/22766-h/22766-h.htm#fig18
    Fig. 18. Leyden Jar
     
  10. Ele1

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  11. nsaspook

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    There's really no difference electrically. The electrical energy is still stored in the field between conductors but instead of having electrons as the charge carrier for conductors on both sides, now one side uses ions. The ion mobility of the electrolyte solution (as the amount of salt is increased) causes it to be a conductor and not much of a dielectric so those polarization effects can be ignored as minor IRT the current capacitance but it does make the value of capacitance somewhat dependent on voltage and time.
     
    Last edited: Dec 3, 2014
  12. BR-549

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    Are we talking Leyden jars or batteries?
     
  13. studiot

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    Thank you ele1, I understand the chemistry of double layers can now look at the info provided.

    BR549 you need to get hold of a good physical chemistry textbook to look this up.
    It is actually very similar in origin to the 'space charge' found in thermionic valves.
    You should also look up the word polarisation and polarisation current in an electrochemical text. This use of the word polarisation is different from the use in dielectrics and electromagnetism.
     
  14. Ele1

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    nsaspook,
    I think your saying the ionized salt makes the water a conductor that allows the electric field from the excess charges on the inner conductor to reach the inner jar surface and form a capacitor with the outer jar conductor using ions on the inside jar surface.

    But how? The jar is such a simple setup, but the explanantion of how it works is perplexing. Theory states the electrical energy should be stored between the excess charges on the surface of the inner conductor and the water and ions in a double layer. The electric field should not be reaching outward.

    In addition, the high potential does not cause the water molecules to break.
     
    Last edited: Dec 3, 2014
  15. BR-549

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    I have always loved chemistry. It tries to understand matter.
    I worked in an environmental analytical lab for 8 years.

    If you would like to physically see how an electrical potential EFFECTS a solid-liquid interface, please YouTube Ferro fluids.

    Most of our modern science is very incomplete.

    Modern science tries to answer questions without knowing the most important and needed one.

    What is matter?

    How can one understand and discern anything without knowing this?
     
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  16. nsaspook

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    Where's the field from the outer conductor going? The electric field energy is from charge separation, charge subtracted from one plate is added to the other so overall the actual amount of charge in the system is unchanged. Because the ions are mobile they will move to electrically neutralize the electrolyte as the field increases across conductors so the actual amount of energy stored within the salt water inner conductor is minor.
     
  17. shortbus

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    Plus the salt water Leyden jars only work until the salt starts to build crystals on the glass surface. The furfaces not below liquid level. When that starts to happen the electrical leakage gets to a point that the jar won't hold or take a charge. And it does happen over time.
     
  18. Storm Fall

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    Correct me if I'm wrong but doesn't the foil and and the salt water solution act as the two metal plates of a capacitor (since the salt water is basically a conductor) and the glass as the dielectric?
     
    Last edited: Jul 19, 2015
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