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The Big Idea
When an electric current passes through a salt solution, the sodium ions will emit a signature yellow light.
Details
When the electrons in an atom are excited, for example when an electric current passes through a substance, the electrons may be pushed into higher energy levels. These electrons then fall back to their ground state, emitting a frequency or frequencies of light that are characteristic of the element that has been excited. In this demo the nails inside the pickle are not touching one another, so the electric current must pass through the salt-filled pickle, thus exciting the sodium ions (salt is sodium chloride or NaCl). The color of light emitted from the glowing pickle in this demonstration is known as the sodium D-line, and it is the same as the light emitted from sodium vapor lamps used in many parking lots.
The fact that different atoms have characteristic emission spectra has allowed astronomers to infer the composition of distant stars by looking at the colors of light emitted from them. A knowledge of these spectra also can be used to determine whether stars are moving towards or away from us, since relative motion will shift these characteristic colors towards the red if the we are moving away from one another (the so called red-shift) or blue if we are moving towards one another (the so-called blue-shift).
Materials and Set-up
- whole dill pickle, kosher dill pickle, or sour pickle
- 2 large nails
- lamp cord with plug attached and other end stripped of insulation 1" down
- surge protector
- extension cord
Be sure nothing is plugged in when you begin. Note that the lamp cord is made of two wires; attach one to each of the nails. Put one nail in one end of the pickle, inserting it about an inch in, and then do the same with the other nail. Make sure the nails are not touching one another; their tips inside the pickle should be one or two inches apart. Move away from the pickle and make sure you aren't in contact with any pickle juice puddles. Check to make sure the surge protector is off and is not plugged in. Plug the lamp cord into the surge protector, then plug the surge protector into an outlet using an extension cord if necessary. Double check all your safety precautions, especially making sure you will not be in contact with any conductor that is connected to the pickle. Turn on the surge protector and wait. In about 30 seconds, the pickle will begin to smoke and glow.
Safety Issues
This is potentially a deadly experiment. You are working with live 110 volt current, so think about everything you are doing. Do not touch the pickle or any part of the apparatus other than the surge protector while the apparatus is plugged in. Note that using the surge protector to turn on and off your pickle allows you an extra measure of control, but that any adjustment of the pickle should be down with the entire apparatus unplugged from the wall.
Wear safety goggles.
Note that the pickle will be very hot after this demonstration.