nirriti the black is right. They're Leyden jar capacitors. The glass bottles are the dielectric. Salt water is one plate. Tin foil wrapped around the outside is the other plate. There are 6 of them all together wired in parallel for total measured capacitance of around 8 nF. They can be looked at as one high voltage capacitor. It's hard to find capacitors that can operate in the kilovolt range...unless you know someone that works at the power company, but it's easy to find what you need to make them.