Physical Properties
Mercury cannot be used below the temperature at which it becomes solid, -38.83 °C (-37.89 °F). If the thermometer contains nitrogen, the gas may flow down into the column when the mercury solidifies and be trapped there when the temperature rises, making the thermometer unusable until returned to the factory for reconditioning. To avoid this, some weather services require that all mercury-in-glass thermometers be brought indoors when the temperature falls to -37 °C (-34.6 °F). To measure lower meteorological temperatures, a thermometer containing a mercury-thallium alloy which does not solidify until the temperature drops to -61.1 °C (-78 °F) may be used.
Read more about this topic: Mercury-in-glass Thermometer
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