Quote Originally Posted by Altair View Post
Mercury-arc rectifier used to power electric trains.
Also used in older cinemas (movie theatres) to rectify for the arc light source in the projectors, one I worked in 35 years ago had a row of these under the old projection room floor, unused by then and still full of mercury, the mercury was worth a bit, but no-one wanted it, as far as I know they're still there.