How to Repair a Mercury Thermometer

Last Updated: July 19, 2022

If the column of mercury (or other indicating fluid) in a thermometer separates, the void will render the indicated temperature inaccurate. Here are some ways to remove the void in the column. Please read all the steps before attempting this.

Steps

1
Inspect the thermometer for damage. Do not use it anymore if it is cracked or damaged in any way. It has served its life and needs to be disposed of properly (see Warnings below).^{[1]
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2
Note the temperature indicated.

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3
Choose a method for repairing the separated mercury.

Method 1

Method 1 of 4:

Cooling

This may be the easiest way to restore the column. However, do note that this method has varied results.^{[2]
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1
Place the thermometer in a refrigerator or ideally, a freezer. If cold enough, it should send the mercury (or other indicating fluid) to the bulb with little else to do. See the next steps if a refrigerator or freezer is not available or did not work.

Method 2

Method 2 of 4:

Warming

This method may take several attempts.

1
Place the thermometer in the sink.
2
Gradually heat the bulb with a hair dryer on warm. The mercury will rise to the top of the thermometer and join together.
3
Allow the thermometer to gradually cool down to room temperature.
4
If you need to take several attempts, just heat and cool gradually. Do not overheat, as the thermometer could burst.^{[3]
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Method 3

Method 3 of 4:

Shaking

This method is fairly reliable as it was often used in hospitals, etc. before the electronic thermometers and disposable temperature strips became commonplace. There is, however, a risk of losing grip of the thermometer while shaking that could result in breakage and spillage of mercury.

1
Firmly grasp the thermometer near the top, so that the bulb containing the mercury (or other indicating fluid) is pointed downward.^{[4]
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2
Rapidly move the thermometer down and sharply reverse direction (and snap the wrist upward). When the thermometer reaches the lowest point of the stroke several times.^{[5]
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3
Recheck the indicated temperature. If the indicated temperature has been reduced from the last time checked, continue shaking the thermometer downward. It will likely require repeating many times before the void in the column has disappeared.

Method 4

Method 4 of 4:

Dropping

This method seems to have the best results, but also risks breakage of the thermometer if dropped from too high or on to a hard surface.

1
Hold the thermometer vertically - with the bulb directed downward.
2
Drop the thermometer on a bed, pillow, or even a towel folded so that it is 8 (or more) times the non-folded thickness. Not more than a one or two foot drop is recommended.^{[6]
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Community Q&A

Question

Is mercury dangerous if ingested?

Community Answer

Yes, do not ingest mercury. It could lead to mercury poisoning, which makes you violently ill.
Question

How long should I keep the thermometer in the freezer?

Community Answer

Keep it in the freezer until the mercury or indicating fluid reaches the bulb.

Warnings

Do not simply "throw away" a device containing mercury. Mercury is a heavy metal, and is highly toxic. In many places, it is illegal to improperly dispose of mercury. Contact your locality's hazard waste office to learn how to dispose of mercury containing thermometers and other devices. Never mix devices that contain mercury in with common household trash.

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Consider discontinuing the use of thermometers containing mercury if it is used for cooking or is a clinical thermometer. Since mercury is highly toxic, using them in food or in the body is discouraged. New electronic thermometers and those that use a red dye and alcohol mixture are much easier to read and safer to use.

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