The mercury-in-glass thermometer was once a standard instrument, valued for its accuracy. However, due to the toxicity of elemental mercury, its use has been phased out globally since the early 2000s. Identifying whether an older glass thermometer contains mercury is important because the substance poses a risk if the casing is broken. Identification focuses primarily on the physical appearance of the liquid column inside the glass tube.
Identifying the Liquid Indicator
The most straightforward way to determine if a glass thermometer contains mercury is to observe the liquid column’s appearance. Mercury is a dense liquid metal that possesses a unique, highly reflective, silver-metallic sheen, often described as bright, liquid silver. This liquid is opaque and easily visible against the background of the thermometer scale.
When you tilt a mercury thermometer, the column moves smoothly, and the meniscus—the curve at the top of the liquid—is very distinct because mercury does not stick to the glass walls. If the thermometer is broken, the mercury will bead up into small, silvery, spherical droplets due to its high surface tension. Observing a liquid that is unmistakably bright silver and highly reflective suggests the presence of mercury.
Common Non-Mercury Alternatives
Thermometers manufactured after the phase-out of mercury often use non-toxic liquids that can be visually distinguished. The most common alternative is colored alcohol, typically ethanol, which is dyed red or blue for visibility. If the liquid in the glass tube is a transparent color, such as red, blue, or green, it is almost certainly an alcohol-based thermometer, which presents a much lower risk if broken.
A slightly more confusing alternative is an alloy called Galinstan, a blend of gallium, indium, and tin. Galinstan is also a silver-colored liquid metal at room temperature, designed to mimic mercury’s appearance. However, Galinstan tends to look duller or grayer than the bright, reflective sheen of mercury. If a Galinstan thermometer breaks, the liquid metal will often smear and leave a residue on the surface rather than forming the distinct, separate, spherical beads characteristic of mercury.
Safe Handling and Disposal
Confirming the presence of mercury means the thermometer must be treated as hazardous waste due to the risk of toxic vapor release if the glass breaks. If the thermometer is intact, immediately place it inside a sturdy, sealed container, such as a plastic jar with a tight-fitting lid or a heavy-duty zip-top bag, to prevent accidental breakage. The container should be clearly labeled “Mercury – Do Not Open” and kept away from children and pets until disposal can be arranged.
Never dispose of an intact or broken mercury thermometer in the regular household trash or recycling bin, as this allows the toxic metal to contaminate the environment. The proper procedure involves contacting your local waste management authority, public works department, or health department. They will provide information on the nearest household hazardous waste collection site or special recycling events that accept mercury-containing devices. Following these guidelines ensures that the mercury is contained and processed safely.