What substance is commonly used in a mercury-in-glass thermometer?

A mercury-in-glass thermometer utilizes mercury as its thermometric liquid due to several advantageous properties it possesses. Mercury has a high coefficient of expansion, meaning it expands and contracts uniformly with temperature changes, enabling precise measurements. Additionally, mercury remains liquid over a wide temperature range, from around -39 degrees Celsius to 356 degrees Celsius, making it suitable for measuring varying temperatures without solidifying or vaporizing. The fact that mercury does not wet glass allows for a clear and easily readable scale within the thermometer.

In contrast, other liquids such as alcohol and water have lower boiling points and may freeze or evaporate under certain conditions, making them less ideal for use in a thermometer designed for a broad temperature range. Ethylene glycol, while usable in some temperature measuring devices, also has a lower boiling point than mercury and presents issues such as toxicity, further limiting its application in traditional thermometers.