OK: here’s my problem. The National Historic Site I work at has the opportunity of receiving from the Canadian Coast Guard a complete lighthouse lantern housing and a first-order Fresnel lens.
This monster is huge; the lens is a good 12 feet tall, weight several tons, and the lantern housing must be pushing 26 feet tall. It’s fully working, with a surprisingly small electric motor rotating the lens around its 500-watt bulb light source.
Here’s the rub: these 19th-century wonders are only able to rotate by floating the lens assembly on a giant tub of mercury. This was one reason that lighthouse keepers (and hatters!) used to go a bit funny, as inhaling heavy metal fumes tends to have a bad effect on your central nervous system.
Parks Canada will not consider allowing us to accept an artifact with such a ticking time bomb of dangerous material as a component essential to operation.
We could remove the mercury and display the light static, but it would be a much more effective interpretive experience to have the light rotatting (besides, it would be really cool, and the other National Historic Sites would be jealous). Changing the mechanism to giant rollers or bearings is out, as our Cultural Resource Management ethics do not allow us to intrude unduly in the historic fabric of an artifact.
So, Dopers: is there a non-toxic substance with the same density as mercury that might be a substitute?