Description: 120 volts is applied across a pickle which then glows.

Stick a fork in each end of the pickle on the plate. Attach the connecting wires to the forks. Plug the variac in and turn up the voltage to approximately 120 volts. The pickle will start to sizzle and steam (hold the microphone near the pickle to pick this up in a large hall). After a short time the pickle will start to glow as the electrical connection across the pickle makes and breaks. The glow occurs at one electrode. Don't let it go too long in a small room - the aroma is distinctive.

The sodium D line may be seen fairly clearly if the pickle is viewed with a handheld spectroscope.

Cautions: The pickle has 120 volts across it - don't touch it.

Concepts demonstrated:

Setup Time: Short

Difficulty/Commitment: Straightforward

Visibility: visible, but a video camera is worthwhile in a large hall

Related demonstrations: Cooking a hot dog

References: PIRA 5D30.30 (also 5E30.30 and 5F15.20)
Video Encyclopedia 18-15
J.R. Appling, F.J. Yonke, R.A. Edgington and S. Jacobs, "Sodium D Line Emission from Pickles", J. Chem. Ed., 70 (3), 250, (March 1993) - shows a comparison of the spectrum from a pickle with the sodium spectrum, no lines other than the D lines were observed.
P.M. Weimer and R. Battino,"The Incredible "Glowing" Pickle and Onion and Potato and...", J. Chem. Ed., 73 (5), 456-457, (May 1996) - i) made a hole slightly larger than the electrode at one end, this end invariably glowed; ii) suggests cutting pickle in half and looking at discharges in gaps around seeds; iii) other veggies marinated in a 15% brine solution
P. Scharlin, A.A. Cleveland, R. Battino, and M.E. Thomas, "Glowing Veggies", J. Chem. Ed., 73 (5), 457-459, (May 1996)
Penn and Teller mention "The Incredibly Dangerous Glowing Pickle Machine" in "How to Play With Your Food", Villard Books, New York, 1992:
"When a regular old dill pickle is skewered on two metal pins and 110 ac, regular old U.S. of A. house current is run through the pins, the pickle glows a ghostly yellow. It's the most beautifully goofy science thing you will ever see. " They point out that Mr Wizard demonstrated the pickle on The Tonight Show, January 24, 1990 and that the pickle was described in Scot Morris' Games column in Omni magazine, December, 1990.
There are many web references, for example:
Lori's Chemistry page
Characterization of Organic Illumination Systems
Investigation into the luminescent effects of high voltage on pickled foodstuffs.