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Fahrenheit’s Hg thermometer cedes field to TCs, RTDs, thermistors (.PDF Download)

March 11, 2021

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Mention temperature measurement to average persons, and they will likely visualize a mercury-in-glass thermometer. They might not know that it was invented in the early 18th century in Amsterdam by Daniel Gabriel Fahrenheit, but they will be familiar with Fahrenheit’s temperature scale, which, after some fine-tuning, places water’s freezing point at 32°F and its boiling point at 212°F, or 180°F higher than the freezing point.

Fahrenheit’s scale continues to hold sway in the United States, although the Celsius scale predominates elsewhere. But alas, the mercury-in-glass thermometer, which had represented the state-of-the-art since its invention in 1714, is being phased out in the 21st century because of mercury’s toxicity. As a sign of the mercury thermometer’s demise, NIST reports that it began an active mercury-reduction campaign in 2007 and stopped calibrating mercury thermometers entirely on March 1, 2011.1

NIST emphasizes that it continues to offer thermometric calibration services for nonmercury devices, including organic-liquid-in-glass thermometers, which you can still purchase. Curiously, Fahrenheit is credited with having helped to perfect an alcohol-in-glass thermometer before turning his attention to the mercury-based instrument.


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