A mercury thermometer is a precise instrument for measuring body temperature, consisting of a sealed glass tube with a bulb containing liquid elemental mercury. The device relies on thermal expansion, where the mercury expands and rises in a thin capillary tube as it absorbs heat. Accurate usage and careful handling are necessary to ensure reliable readings and mitigate safety risks associated with potential breakage. The thermometer’s design maintains the peak temperature reading, requiring a specific preparation technique before each use.
Preparing the Thermometer and Taking a Reading
Before taking a measurement, the thermometer must be prepared to ensure the mercury column is set at a low starting point. First, clean the glass bulb and lower stem with cool, soapy water or rubbing alcohol, then rinse thoroughly. Because a constriction near the bulb prevents the mercury from falling after a reading, the device must be manually reset.
To reset the column, a process known as “shaking down” is required, using centrifugal force to push the mercury back into the bulb. Grip the end opposite the bulb firmly and execute a quick, sharp snap of the wrist downward. Repeat this action until the silver mercury line falls below 96°F or 35.5°C. This ensures the reading starts well below normal body temperature.
The placement method affects both the measurement time and the resulting temperature value. For an oral reading, place the bulb deep under the tongue toward a heat pocket at the back of the mouth, keeping the lips closed for three to five minutes. Rectal temperature, considered the most accurate, requires lubricating the bulb and inserting it about one inch into the rectum for two to three minutes.
For an axillary, or underarm, reading, place the tip in the center of the armpit, ensuring it touches skin only, and hold the arm tightly against the body. This method is the least accurate and requires the longest measurement time, typically four to ten minutes. Regardless of the method chosen, hold the thermometer securely in place for the full duration to obtain a stable reading.
Understanding the Temperature Scale
Once the measurement is complete, read the thermometer quickly before the mercury begins to contract. Hold the thermometer at eye level and slowly rotate it until the fine silver line of mercury is visible against the etched markings on the glass stem. Many thermometers feature both Fahrenheit (°F) and Celsius (°C) scales, with lines often representing two-tenths of a degree.
Reading the scale at a 90-degree angle to the column prevents parallax error, which is the apparent shift in position when viewed from different angles. Read the mercury line at the point where its meniscus meets the nearest etched line to ensure precision. Normal human body temperature is around 98.6°F or 37°C, though this can vary depending on the time of day and the measurement site.
A reading significantly above 100.4°F or 38°C is categorized as an elevated temperature or fever, suggesting the body is fighting an infection. The scale is designed to register temperatures within the clinical range, allowing for the identification of both normal and elevated readings.
Safe Handling and Storage of Mercury Thermometers
Proper handling is necessary to prevent accidental breakage and exposure due to the toxicity of the elemental mercury inside. Always hold the glass tube securely during use and keep it away from edges or surfaces where it could be dropped. Never leave a mercury thermometer unattended, especially around children or pets, as the glass is fragile and the mercury is a hazardous substance.
For storage, return the thermometer to its protective case immediately after cleaning and keep it in a cool location out of the reach of children. Storing it cool helps ensure the mercury remains contracted, making the “shaking down” process easier before the next use. These devices are being phased out in many regions due to the health and environmental risks posed by mercury vapor if the glass breaks.
Protocol for Handling a Broken Thermometer
If a mercury thermometer breaks, immediate and careful action is required because elemental mercury releases toxic vapor. First, evacuate all people and pets immediately, and ventilate the room by opening windows and closing off internal doors. Cleanup must be performed wearing disposable gloves and old clothing that can be discarded afterward.
Never use a vacuum cleaner or a broom to clean up spilled mercury, as this will aerosolize the toxic metal and spread the vapor and tiny beads. Instead, use a stiff piece of paper or cardboard to gently push the beads together into a single, larger pool. An eye dropper or adhesive tape can then be used to collect the tiny, silvery droplets, as mercury tends to adhere to itself.
Place all collected mercury, glass fragments, and cleanup materials, including gloves and tape, into an airtight container. This could be a sturdy, double-bagged plastic bag or a glass jar with a tight-fitting lid. Label the sealed container as “Hazardous Waste” and store it outside the living area until proper disposal. Contact the local household hazardous waste facility for instructions, as mercury cannot be thrown in the regular trash or poured down a drain.