What you see here is a spent propane torch tank with a 1-inch (2.5cm) ball bearing glued to it with a 1/4-inch (6mm) bearing glued to that. I stripped the propane tank with paint stripper, but this is unnecessary as you can just scrape off the paint where the ball bearings go. The Leyden jar is just a common quart sized polyethylene bottle cut off at the top. The electrode is an ordinary empty soda can turned upside down, stuffed into a styrofoam coffee cup. The coffee cup just acts as a gasket to hold the can in place. A piece of wire hanging from the soda can tab connects to about three inches of salt water in the bottom of the bottle through a hole in the styrofoam cup. Both the propane tank and the Leyden jar sit atop a strip of aluminum foil. That's it.
This device is charged with a 3 1/2 foot long piece of 1-inch PVC pipe rubbed with a 1-foot long sleeve of the cheapest, roughest paper towel you can lay your hands on. I usually further wrap the bottom of the paper towel sleeve with a thick layer of cotton cloth to provide higher resistance so as not to bleed off too much of the charge to my hand, increasing the performance even more. The long sleeve is the key here. If you just grab a piece of cloth and rub the pipe, you get some nice little tingly sparks. But adding the sleeve increases the performance by at least a factor of ten. I have measured voltage as high as 250kV with a short circuit current (to ground) of as high as 20µA on the forward stroke of the pipe through the sleeve. More typical measurements are about 150kV and 10µA-12µA. Of course, the disadvantage of this compared to an actual electrostatic machine is that the current and voltage are not continuous. Therefore, the the charging setup can't have any sharp points, or the charge will bleed off through corona leakage as fast as you charge it up. The soda can performs amazingly well as a Leyden jar electrode, as long as the sharp parts are buried inside the bottle. It will hold to about 150kV before it begins to hiss and spit.
The picture was taken with a digital video camera under bright fluorescent light. The sparks are not quite as bright as they appear in the pictures, but they are nevertheless quite impressive to the uninitiated in electrostatics, not to mention being quite loud. These sparks are 5 1/2 inches (14cm) long, but under optimum conditions I have made sparks as long as seven inches (18cm). I think with a little tweaking of the configuration, they might be much longer.
Incidentally, notice the small sparks snaking around the water level at the bottom of the bottle.
The reasons of the success of the procedure were, I believe, dry air, the long tube, the positive terminal ending on a small ball, and the sleeve formed in the friction pad, that impedes discharges of the tube back to the friction pad. Mr. Foster is preparing a web site with more details of his procedure.
Created: 17 February 2001
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