On Feb 16, 12:56 pm, Frank Erskine
wrote:
On Sun, 15 Feb 2009 20:22:09 +0000, Andy Champ
wrote:

I'm not sure what Matty saw. Surely mercury would evaporate over enough
time? And I'm really not sure how you clean it. Kind of hard to polish
a liquid!

A mercury switch has a curved or bent glass tube with 'contacts'
typically at the middle and one end, and obviously containing a bit of
mercury. As it's tilted the mercury bridges the contacts to complete
the circuit.

The mercury switch was in a 1975 Jaguar XJ6. After about 15 years the
mercury was coated in gunk. Fortunately for DIY purposes the switch
was easy to take apart and clean. I think I squeezed the mercury
through a small hole in a piece of cloth and it became shiny again.
The switch was fixed for nothing, and quicker than going for a drive
to a spare parts shop, even if the shop had such a device.