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A balmy Monday in the office

What is this and how does it work?

This is a liquid crystal thermometer. It's the kind of thermometer you'd see attached to a fish tank. It uses heat-sensitive liquid crystals to indicate temperature.

Liquid crystals are crystals that behave mechanically like a liquid but have the properties of a crystal. Changes in temperature cause the color of the crystal to change.

As you can see in the photo at left, it's somewhere near 78 degrees Fahrenheit at my desk. Or maybe closer to 75. That's one of the drawbacks of a liquid crystal thermometer; it's sometimes a bit ambiguous. (After about 10 minutes, the thermometer stabilized and only the 26 C/78 F appeared, which I'll accept because it's a pleasant kind of tropical at my desk right now.)

This thermometer differs from a mercury thermometer - the kind you likely used as a kid when you were sick. Mercury thermometers are glass tubes with a mercury-filled bulb at one end, like the one in the photo at right. When the mercury heats up, it expands (thanks to the tendency of matter to expand when it is heated). Because the bulb is already full of the element, the expanding mercury climbs up an open cavity in the sealed tube. At the point where the mercury stops rising, hash marks on the calibrated instrument indicate the temperature.

Though mercury thermometers work well, they are being phased out and even banned in certain parts of the world because mercury is toxic to humans. This makes digital and liquid crystal thermometers, among others, all the more desirable.

In addition to being stuck to the walls of your fish tank, liquid crystal thermometers are also sometimes found on your fingers - in the form of mood rings. That's right; the 1970s fad for your digits is really just a liquid crystal thermometer. Like the flat thermometer above, the stone in the mood ring changes color in response to your body temperature. Whether or not it is an actual indicator of your mood, though, is another story.


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