In some thermostats, mercury switches are used to turn the heating and cooling system on and off. The mercury is contained in a small glass vial, or ampoule. The "How Stuff Works" Web site explains how a mercury thermostat functions.
The most common mercury switch thermostat is the round Honeywell T-87. Other mercury thermostats are made by White Rodgers, General Electric and other manufacturers.
While most mercury thermostats were manufactured between 1953 and 1990, some are still being made and sold.
For new thermostats, check on the package. Thermostats with mercury will have the “Hg” sign for mercury on the packaging..
For thermostats in use, take off the cover and look inside. If there is a glass ampoule (or ampoules) containing a silvery substance, the thermostat has a mercury switch and the silvery material is elemental mercury.
In Washington State, some sales restrictions (Revised Code of Washington 70.95) apply to mercury thermostats.
For more information contact Taylor Watson, Health and Environmental Investigator, at email@example.com.