Mercury thermometers are traditional measuring devices that utilize elemental mercury, a liquid metal sealed within a glass tube, to indicate temperature. The principle relies on the uniform expansion and contraction of this liquid metal as the ambient temperature changes. For a clinical thermometer, the measurement process leaves the mercury column at the highest recorded temperature, necessitating “resetting” to force the liquid back into the storage bulb before the next use. This manual reset is required because a narrow constriction just above the bulb prevents the mercury from falling on its own after a peak reading.
Step-by-Step Guide for Lowering the Column
Resetting a mercury thermometer requires a specific, controlled motion to generate the necessary force to pass the mercury through the internal glass constriction. Hold the thermometer firmly by the end opposite the bulb, using your thumb and forefinger to ensure a secure grip. The bulb end should be pointed downward and away from any person, pets, or hard surfaces that could cause breakage. The goal is to apply centrifugal force, which overcomes the restriction designed to hold the peak temperature reading.
Use a sharp, snapping motion of the wrist, similar to cracking a whip. This motion is a quick downward flick, providing the rapid acceleration needed to move the dense liquid metal. Check the reading after three to five snaps, ensuring the column has descended sufficiently.
The mercury column needs to be forced down below the standard ambient temperature or, for a fever thermometer, below 96 degrees Fahrenheit (35.5 degrees Celsius). If the column remains high, repeat the wrist-snapping motion until the mercury is safely contained within the bulb reservoir. Failing to lower the column completely will result in an inaccurate, elevated temperature reading during the next measurement.
Critical Safety Precautions When Handling
Handling any mercury-containing device demands caution due to the liquid metal’s inherent toxicity. Mercury can vaporize into a gas that poses a serious inhalation hazard. Avoid dropping or knocking the thermometer against hard surfaces, as this can easily fracture the thin glass casing.
Always store the thermometer in its protective case and keep it in a location inaccessible to children and pets. If the thermometer breaks, the immediate priority is to ventilate the area by opening windows and doors, then having all people and animals leave the room. Never use a vacuum cleaner or broom to clean up the spill, as this will disperse the mercury beads and increase the toxic vapor concentration in the air.
Cleanup Procedure
For cleanup, put on disposable gloves.
- Use stiff paper or cardboard to gently push the silvery beads together into one large droplet.
- Use an eyedropper to collect the mercury, or adhesive tape to pick up smaller, scattered particles and glass fragments.
- Place all collected materials, including the gloves and cleanup tools, into a sturdy, airtight container.
- Contact local authorities for hazardous waste disposal instructions.
Safe Disposal and Modern Alternatives
Due to the environmental and health risks associated with mercury, these thermometers are classified as Household Hazardous Waste (HHW) and cannot be placed in regular trash. Disposal requires contacting your local municipal waste authority or health department to locate an official HHW collection site or event. Regulations governing the disposal of mercury-containing products vary significantly between states and localities.
Many manufacturers have ceased producing mercury thermometers, and several effective alternatives are now widely available for home use.
Types of Alternatives
- Digital thermometers use electronic sensors called thermistors to provide fast, accurate readings.
- Infrared models, such as temporal artery or ear thermometers, measure heat waves and offer non-contact temperature measurement.
- Glass thermometers contain non-toxic liquids, such as alcohol or a gallium-indium-tin alloy, which mimic the function of mercury without the associated danger.
These modern devices eliminate the need for the specialized handling and disposal required for mercury-filled instruments. Replacing older mercury thermometers with these safer options safeguards both household occupants and the environment.