The liquid in most common thermometers is mercury or alcohol. Mercury is a silvery-white metal that is liquid at room temperature. It is used in thermometers because it expands and contracts evenly with changes in temperature, making it easy to read the temperature. However, mercury is toxic, so mercury thermometers are being phased out in favor of alcohol thermometers. Alcohol is a clear liquid that is made from fermented sugars. It is less toxic than mercury, and it also expands and contracts evenly with changes in temperature, making it suitable for use in thermometers.