Mercury Tilt Switches were common on the
surplus market until recently. They are usually a small glass amplule
from approximately 0.3 to 3 milliliters in volume. Sealed inside are
two electrodes and a blob of mercury, the only metal which is liquid at
room temperature. When the switch is tilted the blob of mercury flows
down the tube and envelops the electrodes, thus completing the circut
and turning on the lamp. Mercury is poisonous and commercial uses of
the metal are quickly declining. Mercury swithes are still in
manufacture.
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