The thermometer has a small bulb filled with either mercury (in older thermometers) or alcohol (in modern ones). When the temperature rises, the liquid expands and moves up the narrow tube.

Mercury in the glass thermometer that we use for checking body temperature is most lethal and can pose serious health problems if accidentally spilt Mercury in the glass thermometer that we use ...

SFU EHS will swap your mercury thermometers with non-mercury alternatives for free. Simon Fraser University is committed to eliminating non-essential uses of mercury and mercury-containing products.