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Thermometers: Choose and Use Guide

It’s easy to select the right thermometer for the task at hand. Start with the requirement that is most important to you and look for the recommendations under that category.


  • Calibrated Thermometers - Fractional Degree
  • Enviro-Safe® Thermometers - As accurate as Mercury

Low Cost:

  • Spirit-filled Thermometers


  • Enviro-Safe Thermometers
  • Teflon-coated Thermometers


  • 6" (165 mm) Enviro-Safe Thermometers
  • 8" (203 mm) Spirit-filled Thermometers
  • Teflon-coated Thermometers (Spirit-filled)

Immersion: (The two types of thermometers are not interchangeable)

  • Partial: For general use, thermometers should be immersed in the test solution up to the line printed on the thermometer.
  • Total: For highest accuracy, the entire thermometer column needs to be immersed in the liquid to be measured. This gives the highest accuracy, but using a total immersion thermometer improperly will result in errors.

Thermometer Separation

All liquid thermometers separate for a variety of reasons. Thermometers in such a condition may be prepared for use by one of the following methods, depending upon the type of separation found.

1. Separation in upper portion of column

For thermometers with maximum range of 260 °C (500 °F) having sufficiently large expansion chamber at top, place thermometer in liquid bath, using a liquid having a flash point well above thermometer’s range. Do not heat bulb with an open flame. With thermometer held in a vertical position, immerse as much of the stem as possible in the liquid. Heat bath slowly until the separated segments and a portion of the main (intact) column enter the expansion chamber at the top. (Be sure chamber is not filled more than half to two-thirds of volume or bulb may break.) With the thermometer in an upright position, gently tap it allowing the gas to rise above the column. Allow the thermometer to cool slowly in an upright position.

2. Separation in lower portion of the column

Submerge bulb only in a solution of dry ice and alcohol (do not cool the stem or column) to retract the liquid into the bulb. Swing the thermometer bulb-down in an arc forcing the gas to rise above the column. A slow and careful return to ambient will probably unite the column. Keep the thermometer vertical during this procedure.