CMS:Mercury arc rectifier
The museum's mercury arc rectifier is not suitable for demonstrations during opening hours, but is operational. When it is working, the tube glows blue and teal and a constantly moving arc through mercury vapor is visible.
An old waffle maker and a few light bulbs are used to provide ballast. When the rectifier is in use, 120 VAC from the wall passes through the waffle maker and light bulbs first which provide resistance before the current passes through the rectifier itself. Without this resistance too much current would flow and a breaker would trip. Light bulbs have an added benefit of showing how much current is flowing depending on their brightness.
Resting on a shelf near the top of the rectifier is a heating element which is powered by the direct current output by the rectifier. All rectified current is converted to heat via this heating element. It can be adjusted to pull more or less current through the rectifier.