Mercury Thermometers Are Going Extinct. What Will Replace Them?

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The National Institute of Standards and Technology (NIST) announced last week that it would stop calibrating mercury thermometers starting March 1 a move that brings the U.S. one step closer to phasing out these temperature-measuring devices for good.

Although mercury thermometers have been mostly phased out of daily home use, the tool, which was invented in the 1700s by Gabriel Daniel Fahrenheit, remains a standard measuring device for many industries, including regulating the temperature of a chemical concoction being made in an industrial lab, and monitoring the temperature in blood banks and vaccine storage facilities.

The problem is that mercury is toxic to humans and to the environment , making spills of this substance a reason for concern. So why did mercury become the main temperature-measuring fluid and what will we do without it?

The mercury thermometer was invented back around 1748 and there was no electricity or digital anything back then, said Greg Strouse, head of the Temperature and Humidity Group at NIST. That thermometer became a dominant thermometer in use and it just became a cultural thing, Strouse said.

The alternative to the mercury thermometer is the digital thermometer, which measures temperature by monitoring changes in electrical properties voltage and resistance of metals inside the device. (Mercury, on the other hand, works by expanding and contracting with increasing and decreasing temperature. With nowhere else to go, this liquid metal zooms up and down a tube inside of the thermometer stick.)

It turns out that this change is for the better for more than environmental reasons: Mercury isn't even the most accurate way to measure temperature. While mercury thermometers can measure temperature within one degree Celsius, digital thermometers can be as accurate as 0.001 degrees C a difference of four orders of magnitude in accuracy.

This changeover won't be a big deal for the average person "In fact, you can't buy [mercury thermometers] anymore," Strouse said. To ease the transition in other settings, NIST is proving the feasibility of the switch and working with each industry to come up with the right electronic replacement.

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