Question

Mercury boils at ${356}^o$C. However, mercury thermometers are made such that they can measure temperatures up to ${500}^o$C. This is done by :

• A. maintaining vacuum above the mercury column in the steam of the thermometer
• B. filling nitrogen gas at high pressure above the mercury column
• C. filling nitrogen gas at low pressure above the mercury column
• D. filling oxygen gas at high pressure above the mercury column

Answer 1

Answer: (B)

By filling nitrogen gas above the mercury column, we are in fact increasing the boiling point of mercury. Mercury that can reach boiling point of ${356}^{o}C$, can now measure up to ${500}^{o}C$. Mercury separation in the capillary of the thermometer is filled by nitrogen gas and nitrogen being inert gas can minimize the oxidation of mercury.