I have some mercury switches

[soldar]

I have some mercury switches. These used to be common 50 years ago but have disappeared. I have no idea what current and voltage they can safely carry or break.

The small ones are a cylindrical glass bulb, about 5 mm diameter and 15 mm long and have a drop of mercury inside. I am thinking of making a float switch with a wine bottle cork stopper. Drill a hole from one end, insert the mercury bulb with thin, flexible cables, well sealed and put the cork pivoting on a wire so when it floats the mercury closes the contacts. The electrical part seems quite straightforward but I need to think about the mechanical part . I need it to not be subject to corrosion and have a heavy base which will hold it in place. I am thinking of a piece of brick cut into a U shape with the float in the center. I need to think about this. Y think I would only use them as sensors with low voltage and current.  Or maybe they could handle, say, 2 Amps at 12 V?

I also have a big mercury switch, (12 x 65 mm) which came from a mechanical timer designed to switch many amps at 220 V. I suppose relay contacts would not last as long due to sparking and corrosion. When this thing tilts over the break is quite fast and I suppose there is no oxygen inside the capsule. It has a central, common terminal and one at each end (NO & NC). When it is horizontal all three terminals are connected so it is "make before break". I cannot think of any practical use for it today but it would be fun to put it to some use where it could be seen and admired in action. I could design an "over center" mechanism so the mercury bulb would only be stable tilted to one side or the other.

"over center" mechanism:

[Gregg]

Tiny mercury switches used to be common for automobile under hood and under trunk lid switches that would automatically turn on the light when the lid was raised.  They were approximately 6mm in diameter and 10mm long and fit in the lamp socket.  Power was from the parking light circuit to prevent battery drain.  Some were glass and some were Bakelite. 
A lot of larger mercury switches were common in the HVAC industry for rotating temperature controls; a common brand was Mercoid.