Volta Hailstorm

This is an electrostatic demonstration which appeared in various incarnations throughout the 19th century; it is called by several names, perhaps the most distinctive being "Volta Hailstorm." I have not found evidence that Alessandro Volta is the originator of the device, but the name serves as well as any.

The device consists of two conducting plates separated by an insulating medium (air, plastic, glass, etc.), between which rest free, lightweight bodies. A high-potential charge presented to the top electrode attracts the neutral, lightweight bodies sufficiently to overcome gravity's hold. Upon striking the top electrode, those bodies, if at all conductive, assume a like charge and are instantly repelled. Reaching the bottom electrode grounds the bodies, whereupon their charge is neutralized and the process begins anew.

This particular example consists of two solid brass electrodes seperated by an acrylic tube. Inside the tube are a few dozen styrofoam balls coated in graphite (to make them somewhat conductive). As the above video shows, it is quite sensitive; the balls begin to jump even as the relatively feeble charge of the electrophorus disk approaches.

I originally used a drinking glass with the bottom cut off as the seperating medium. I struggled with this device for days before I learned more about glass, especially as pertaining to its suitability as an insulator in electrostatic experiments (see Leyden Jar page for detail). I was only able to make the hailstorm work when heated at length, almost until it was too hot to comfortably handle. Even after heating, the device's performance was erratic and unsatisfactory. The extensive heating also dried out the styrofoam balls, making them less conductive than if they retained some moisture from the air. Breathing upon the balls helped increase their reaction but trapped water vapor inside the glass, undoing my work to thoroughly dry it! Ultimately, I yeilded; having no glass jars of an appropriate quality and size, I resorted to plastic. The defeat is mitigated by the outstanding and consistent results I now enjoy.

Created by Sean Corron, April 2, 2011.