Mercury Switch Doorbell

I have held on to this custom doorbell switch and re-installed it in various places for nearly a decade now. It was originally fabricated by engineer and artist Brian Matthews, aka Pirate Brian. You can see more of his work here.  It is a fantastic contraption and includes an interesting example of a mercury switch, a traditional type of tilt switch now somewhat harder to find owing to our improved understanding of the toxicity of mercury.

Though toxic, mercury has some unique attributes that make it intriguing for switch applications. Like all other metals, it is a conductor of electricity; unlike all other (pure) metals, it is a liquid at room temperature. In the image above, you can see the liquid mercury housed inside a sealed glass container, and copper ring terminals (background) on the ends of the switch wires, which are encased in ceramic insulators connected to the container’s two contacts.

The container has been attached to a pivot connected by chain to, and operated by, a lever-style handle, which in turn drives a mechanical doorbell. When the handle is released the switch springs back to open position, the mercury flows back to one side of the container, and the current is broken. Mercury tilt switches were used in clothes irons, for example, switching one way when tilted horizontally, and switching the other when placed upright.

From liquid metal fountains to switches, mercury has been used in the past for both its aesthetic and functional qualities. Today we know it should be handled with great caution. Mercury switches can still be found in gas ranges, thermostats, gas water heaters and furnaces, and even older washing machines. Before disposing of expired appliances you should check to make sure they do not still contain mercury, and some districts and states even have laws outlining safe disposal procedures.