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What Is a Mercury Thermometer?

Mercury thermometers contain between 0.02 ounces to 0.1 ounces of liquid mercury.
Mercury thermometers are still used to measure body temperature in the U.S.
A mercury thermometer is a termperature measuring device.
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  • Written By: Summer Banks
  • Edited By: Michelle Arevalo
  • Last Modified Date: 06 October 2014
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A mercury thermometer is a tool used for measuring temperature. Gabriel Fahrenheit invented it in 1714, and his basic model is still used today in medical and non-medical settings. Typically, such a device is a glass tube filled with mercury. The majority of this substance is found in a metal tip, which is used as a warming device for the thermometer.

Most of these thermometers hold between 0.02 ounces (0.5 g) and 0.1 ounces (3 g) of mercury. Thick glass generally encases the temperature-sensitive liquid metal. When a mercury thermometer is placed outdoors or in the body, the metal tip heats and mercury stretches along the length of hollow space within the tube. Higher temperatures cause mercury to grow longer, while low temperatures cause it to fall. These thermometers are usually marked with temperature readings on the Fahrenheit or Celsius scale.

These devices are commonly used in medicine and meteorology. Medical doctors often use the maximum mercury thermometer to measure human body temperature. This type can be used either orally or anally.

A maximum mercury thermometer works in much the same way as a standard thermometer, but the mercury does not shrink back into the tip when removed from a heat source. This allows temperature readings to be kept until mercury is forced back into the tip by centrifugal force, or shaking the thermometer with the head pointed toward the floor. Nitrogen gas in the glass tube is what holds the mercury in place.

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A mercury thermometer may also be used by meteorologists to measure air temperature. Standard mercury freezes at -37.89°F (-38.83°C). In order to measure temperatures below this point, meteorologists will often mix mercury with thallium alloy. Thallium reduces the freezing point to -78°F (-61.1°C). If mercury freezes, nitrogen can be caught behind the metal causing the thermometer to stop working.

With only between 0.02 ounces (0.5 g) and 0.1 ounces (3 g) of mercury in each thermometer, health risks from oral consumption are thought to be low. Inhalation of mercury at these levels could cause dangerous side effects, however. Due to the dangers associated with mercury poisoning, many countries in Europe have chosen to ban mercury thermometers for medical use.

The United States has not banned mercury thermometers in a medical setting. The American Academy of Pediatricians and the United States Environmental Protection Agency, however, have suggested alternative temperature-measuring devices for personal use. There have been no U.S. bans, as of 2009, on mercury thermometer use in professional medical settings.

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Discuss this Article

Sara007
Post 6

If you have children and they are scared of having their temperature taken in a traditional method you can buy nifty plastic strip thermometers. These thermometers work exactly like bandages and you stick it to your child's skin for a few moments and it gives you a temperature reading. They are painless to use and disposable so you don’t have to worry about cleaning anything.

I really loved the idea of plastic strip thermometers because with mercury thermometers I was always worried about my children dropping the glass vial and breaking it. With the strips you stick on you no longer have to worry about any of that.

lonelygod
Post 5

I have always preferred mercury thermometers because of how easy they are to use. I think as long as you are careful there is no need to drop $50 or more on a digital thermometer.

I have found that the digital thermometers that you press against your forehead are absolutely terrible. I am not sure if it was just the brand that was being used on us at work, but it never got a reading correct without multiple tries, and even that final reading was questionable.

If you do have a mercury thermometer just make sure to wipe it off with a new alcohol swab after each use so you can disinfect it.

miriam98
Post 4

@allenJo - Ask your doctor what medical thermometer they use. I know the hospitals use some digital ear thermometers that are supposed to be rated very high for accuracy, and as a consumer you can buy these models yourself.

I think you can get them for under $50. Some of them will deliver temperature readings within two to three seconds rather than forcing you to wait for almost a minute as with other consumer grade digital thermometers.

allenJo
Post 3

I know that the ear thermometer has become the instrument of choice as physicians got away from the more invasive rectal thermometer, but I wonder if the they are as effective as they claim to be.

At home I’ve taken different temperature readings when using the ear thermometer and got different results each time, usually off by a degree or two – sometimes within the same hour. Maybe I’m not using it properly, I don’t know.

The ear thermometer is cleaner and less invasive than an oral thermometer, which is what it has going for it, but if I can’t be sure that the temperature is accurate it’s not much use.

Azuza
Post 2

@SZapper - I remember when the digital thermometers for at home use came out too.

I know mercury thermometers are still alive and well in science classes! I remember using them in every lab science class I ever took in high school and college. I remember they did always remind us to be careful and not to drop them.

SZapper
Post 1

I'm pretty sure I remember when they started phasing out mercury thermometers for at home use. I remember when I was very little we used a mercury thermometer and my mom always warned us to be very careful with them.

Then when I got a little bit older digital thermometers came out and we replaced our mercury thermometer. Like everything else electronic I remember digital thermometers used to be a little bit more expensive than they are currently!

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