Rejoining Separated Thermometer Columns

Rejoining Separated Thermometer Columns

Rejoining Separated Thermometer Columns

Rejoining Separated Thermometer Columns

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Mike Isley Product Developer

March 2017


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One of the most common problems with laboratory thermometers is column separation due to improper storage, vibration, or accidental dropping. It is possible to join a separated column with a few simple techniques. These are methods for joining separated columns using mercury-filled or spirit-filled thermometers.

A petroleum-based liquid is mixed with a dark-colored dye to provide contrast when reading the scale. The common spirit-filled thermometer uses a petroleum-based liquid. Mercury-filled thermometers are toxic and are no longer being sold by many companies. Mercury-filled thermometers should be handled with care. Keep a mercury collector handy.


  • Gloves
  • Goggles
  • Bunsen Burner (for heating method only)
  • Test Tube Rack or Thermometer Storage Rack
  • Dry Ice (for cooling method only)
  • Alcohol (for cooling method only)
  • Small Beaker (for cooling method only)


For mercury-filled thermometers

Cooling method

  1. Add enough dry ice and alcohol to a small beaker to cover the thermometer’s bulb.
  2. Immerse only the thermometer’s bulb into the dry ice and alcohol.
  3. As the bulb cools, let all the mercury column escape.
  4. Place the thermometer in a rack with test tubes. The separated liquid will return to a solid column as the thermometer warms to room temperature.

For spirit-filled thermometers

Tapping method

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Hold the thermometer upright and gently tap it against the palm of your gloved hand above the column separation. This should cause the upper separated column of the thermometer to separate from the glass walls. It will then fall back down and join the main one.

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Another method is to hold your thermometer vertically, and allow the bulb’s drop onto a soft surface, such as a computer mousepad. If this fails, you can try the heating method below.

Heating method

  1. Wearing gloves and safety goggles, ignite a Bunsen burner and move the thermometer’s bulb in and out of the heated air directly above the flame. See Fig. 1. Note: Do not insert the bulb into the move the bulb over the flame and then away repeatedly for slow heating. Rejoining Separated Thermometer Columns Figure 1 Heating the thermometer’s bulb.
  2. Make sure the separated columns move slowly up the capillary tube. All columns should be joined by the time the first column segment enters into the expansion chamber.
  3. Allow no more than 3/4 of the expansion chamber to be filled with liquid. See Fig. 2. It is important not to heat the bulb too much. If the liquid column rises quickly and fills up the expansion chamber, it could burst and cause liquid to be expelled. Rejoining Separated Thermometer Columns Figure 2 The thermometer’s expansion chamber.
  4. Once the chamber is filled to 3/4, turn the thermometer upside down and away from a burner to allow the column to cool.
  5. The thermometer should be placed upright on a test tube rack. Allow it to cool to room temp. If there is still a separation, repeat the procedure and let the thermometer cool in an upright position.

How to avoid column separation

When storing thermometers, it is best to keep them upright in a storage rack, or if stored in a drawer, at 15º from horizontal (expansion chamber end up). This angle allows gravity to hold the liquid column together. Avoid vibration and drops on your thermometers.

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