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

The correct option is B filling nitrogen gas at high pressure above the mercury column

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.