Mercury does freeze; its freezing point, according to Denver University, is -38.9 degrees Celsius (-38.02 degrees Fahrenheit). The idea that mercury does not freeze may be related to the fact that mercury is used in thermometers, but in fact, mercury's relatively high freezing point is a disadvantage compared to other substances that can be used in thermometers and have a lower freezing point.
Mercury, the poisonous silvery substance named for the Roman god responsible for guiding dead souls to the underworld, is a liquid at room temperature, and it is the only pure metal with this characteristic. However, that doesn't mean that mercury doesn't freeze. It does have a relatively high boiling point (356.58 degrees Celsius, or 673.844 degrees Fahrenheit), but it does freeze at a temperature that is colder than water. However, compared to alcohol, which is a safer alternative as a thermometer component, mercury has a relatively high freezing point. Alcohol freezes at -114 degrees Celsius (-173.2 degrees Fahrenheit), making it a more versatile material for measuring cold.
Though it has a poisonous vapor, mercury does have some advantages over alcohol as a thermometer medium. It has a much higher boiling point than alcohol, which boils at 60 degrees Celsius (140 degrees Fahrenheit). It is also durable, accurate and easy to calibrate.