Why was mercury historically useful in thermometers?

Mercury was historically useful in thermometers primarily because it does not wet or cling to glass, which allows for accurate readings. Additionally, it exhibits rapid and uniform volume expansion throughout its liquid range, providing consistent measurements across varying temperatures.1

While these physical properties made mercury an effective medium for temperature measurement, its use has been largely discontinued in favor of electronic digital thermometers. This shift is essential because mercury is a toxic substance, and its presence in household and medical instruments poses significant health and environmental risks. Prioritizing public safety and environmental health is a fundamental ethical imperative, which is why the transition to safer, non-toxic alternatives is a necessary advancement in technology.12