Leyden Jar – What It Is and How to Make One


How to Make a Leyden Jar
Make a Leyden jar using a plastic bottle, salt water, aluminum foil, and a metal screw.

A Leyden jar, also known as a Leiden jar or Kleistian jar, is a simple device that stores static electricity. It is an early form of a capacitor, an essential component in modern electronic circuits. A basic Leyden jar consists of a glass container lined with conductive material both inside and outside, a metal rod that connects to the inner lining, and usually a liquid such as water.

Historical Background

Before the Leyden jar’s invention, scientists were exploring electrostatics, a field focused on studying stationary electric charges. Early researchers used simple tools like rubbed amber rods for producing static electricity. However, storing this electricity for later use was a significant challenge.

In 1745, German cleric Ewald Georg von Kleist discovered that a glass jar filled with alcohol and fitted with a nail could store static electricity. Around the same time, Dutch physicist Pieter van Musschenbroek of the University of Leiden (Leyden) independently developed a similar device, which led to its name, the Leyden jar. Benjamin Franklin later conducted extensive experiments with the Leyden jar, enhancing the understanding of its function and furthering the study of electricity.

Design and Operation

Leyden Jar Construction
Source: William Henry Marchant 1914 Wireless Telegraphy

A simple Leyden jar comprises:

  • A glass jar with a conductive metal coating on the inner and outer surfaces.
  • A metal rod extending through the jar’s top, touching the inner metal coating.
  • Water or another nonelectrolyte liquid inside the jar.

How a Leyden Jar Works

The Leyden jar operates on the principle of electrostatic induction. When the metal rod is charged, electrons accumulate on the inner metal coating, creating a negative charge. The outer coating, connected to the ground, becomes positively charged due to the repulsion of electrons. This setup allows the jar to store a significant amount of electrical energy, which is released by creating a conductive path between the inner and outer coatings.

The Leyden Jar and Capacitors

A Leyden jar is essentially a primitive capacitor. Capacitors store electrical energy in an electric field between two conductive plates separated by an insulating material (dielectric) or even a vacuum. The Leyden jar’s glass acts as the dielectric, and the metal coatings serve as the conductive plates.

Capacity

The capacity of a Leyden jar, or its ability to store charge, depends on factors like the size of the jar, the thickness of the glass, and the type of conductive material used. Typical Leyden jars store a few nanofarads (nF) to microfarads (μF) of charge. Early Leyden jars stored between 20,000 and 60,000 volts.

Leyden Jar Uses

Leyden jars were used extensively in early electrical experiments and demonstrations. They were crucial in studying electrostatics, understanding electric charge, and developing early theories of electricity. In the Victorian era, the jars also found use in electrotherapy. Later, the devices set the stage for spark-gap transmitters and modern capacitors.

How to Make a Leyden Jar

Using an electrolyte, like salt water, is much easier than coating the inside of a bottle with metal. To build a simple homemade Leyden jar, you’ll need:

  • A plastic or glass bottle
  • Salt water (acts as the electrolyte)
  • Aluminum foil
  • A steel screw (for the metal rod)
  • PVC pipe and cotton dish towel (for generating static electricity)

There a few things to note about the materials and possible substitutions. It does not matter what you use as a container, providing it is not an electrical conductor (e.g., an aluminum can). However, the thinner the material, the better, which is why plastic bottles are ideal. Use any electrolyte in place of salt water, if you like. A steel screw is ideal for drilling through the bottle cap, but any conductive metal works.

There are several alternatives for the PVC and cotton combination, including:

  • Rubber balloon and hair, fur, or wool
  • Acrylic and hair, fur, or wool
  • Glass and a silk cloth
  • Teflon and wool
  • Walking across a carpeted floor wearing socks

Construction

  1. Wrap the aluminum foil around the exterior of the plastic bottle, covering about half of its height.
  2. Fill the bottle with salt water to the same height as the foil. Salt has low solubility in cold water, so dissolve some salt in warm or hot water. The amount of salt is not critical.
  3. Insert the steel screw through the bottle’s cap, ensuring it touches the salt water inside.
  4. Seal the cap tightly to secure the screw in place.

Charging and Discharging

  1. Rub the PVC pipe with the cotton dish towel to generate static electricity. Alternatively, use any of the other options, such as rubbing a balloon on your hair.
  2. Touch the charged PVC pipe (or balloon, etc.) to the metal screw to transfer the charge to the salt water inside the bottle. (Note: You also get charge if you simply place the PVC or balloon near the screw. This works well when you don’t want much charge accumulation, for safety.)
  3. You have a few different options for discharging the Leyden jar. Using this simple set-up, which produces a low voltage, one option is simply touching the screw. You’ll get shocked! A safer option is using a screwdriver with an insulated handle. If you discharge the jar in a darkened room, you’ll see the spark.

Safety Considerations

  • Always handle Leyden jars with care, as they potentially store a significant charge.
  • Avoid touching the metal parts directly to prevent electric shocks.
  • Discharge the jar safely before handling it by connecting the inner and outer conductors.

While the design of this homemade jar is unlikely to do more than cause a painful shock, improper use of large Leyden jars is potentially deadly.

Common Errors and Improvements

  • Maximize electrical storage capacity by insuring that the aluminum foil and salt water are at the same height.
  • Ground the outer foil to prevent shocks. You can connect a wire between the foil and a faucet (which should be grounded) or a spike driven into the literal ground. Grounding the outer foil also improves the capacity of the jar.
  • Make sure the bottle cap is not conductive.
  • Don’t get the foil layer too close to the metal rod (screw) to prevent arcing current between them.
  • Make sure the screw makes contact with the salt water.
  • Improve efficiency by using a larger bottle, increasing the surface area of the aluminum foil, or using a better conductor for the rod.
  • The thinner the dielectric, the better. You get better storage capacity if the walls of the bottle are thin.

Leyden Jar Experiment Ideas

Channel Benjamin Franklin and explore the physics of a Leyden jar yourself. Turn the project into an experiment by making observations about the jar, deciding on changes you can make, predicting the outcome, and performing tests:

  • Test different liquids (e.g., distilled water, vinegar) to see how they affect the jar’s capacity. What happens if the jar is empty (contains only air)? What if you use wax or another solid?
  • Explore the material or configuration of the metal electrode. What can you use instead of a steel screw? Options include copper wire, an aluminum-coated ping pong ball, or silver wire. What happens if you cover the screw with a flat strip of aluminum?
  • Vary the size of the bottle and observe the changes in charge storage.
  • Vary the composition of the bottle (glass or plastic) or its thickness.
  • Experiment with different materials for the outer coating (e.g., aluminum tape, copper tape, conductive paint).

References

  • Addenbrooke, G. L. (March 1922). “A study of Franklin’s Experiment on the Leyden jar with movable coatings”. Philosophical Magazine. 6th Series. 43 (255): 489–493. doi:10.1080/14786442208633901
  • Dummer, G. W. A. (1997). Electronic Inventions and Discoveries (4th ed.). Institute of Physics Publishing. ISBN 978-0750303767.
  • Heilbron, J.L. (1979). Electricity in the 17th and 18th Centuries: A Study of Early Modern Physics. University of California Press. ISBN 978-0-520-03478-5.
  • Mills, Allan (December 2008). “Part 6: The Leyden jar and other capacitors“. Bulletin of the Scientific Instrument Society (99): 20–22.
  • Silva, C.S.; Heering, P. (2018). “Re-examining the early history of the Leiden jar: Stabilization and variation in transforming a phenomenon into a fact”. History of Science. 56 (3): 314–342. doi:10.1177/0073275318768418