Extending the range of a mercury-in-glass thermometer with pressurized nitrogen Ordinary mercury thermometers read up to about 120°C. When nitrogen is filled above the mercury under pressure to suppress evaporation and prevent thread breakage, up to what temperature (°C) can measurement typically be extended?

Introduction / Context: Liquid-in-glass thermometers are simple and robust, but mercury begins to evaporate and the column can break at high temperatures. Filling dry nitrogen above the mercury under pressure suppresses evaporation and stabilizes the column, enabling an extended temperature range for industrial duty.

Given Data / Assumptions:

• Ordinary mercury-in-glass range ≈ up to 120°C.
• Nitrogen is added above the mercury, under pressure.
• We seek the typical upper temperature limit achieved by this modification.

Concept / Approach: Pressurizing the space above the mercury raises the boiling point and curbs vapor formation. It also reduces the risk of a broken mercury thread by applying a stabilizing pressure. With suitable glass and construction, industrial “gas-pressure filled” mercury thermometers commonly reach into the 300–350°C region with reliable readings.

Step-by-Step Solution:

Verification / Alternative check: Manufacturers’ catalogs list nitrogen-filled mercury thermometers with upper ranges around 300–360°C depending on stem and bulb design, confirming 350°C as a representative value.

Why Other Options Are Wrong:

Common Pitfalls: Confusing gas-filled “remote” bulb instruments (which can indicate higher temperatures via filled systems) with a simple mercury column thermometer; here we discuss nitrogen above the mercury in a direct-reading glass thermometer.

Final Answer: 350