Mercury thermometers are devices used to measure temperature. They contain a glass tube filled with liquid mercury, which expands and rises in the tube as the temperature increases. The scale on the thermometer allows users to read the temperature accurately. These thermometers are commonly used in medical settings and for weather measurements. However, due to the toxicity of mercury, many places are phasing them out in favor of safer alternatives, such as digital thermometers or alcohol-based thermometers. Proper disposal is essential to prevent environmental contamination.