Mercury cannot be used to measure temperatures lower than -39 �C (as mercury freezes at that point) or temperature higher than 356.7 �C (the boiling point of mercury). Mercury has been replaced largely by alcohol for use in thermometers. Ethanol is cheaper and safer than mercury and can be used as low as -80 �C. However, ethanol boils at 78°C (172.4°F), which means its upper limit is much lower than mercury thermometers.