Reuniting Separated Mercury Columns
The largest single cause for the failure of precision thermometers
in the lab is due to separated mercury columns. This can occur in transit
or in the lab. The life of the instrument can be greatly extended if the
following procedures are rigidly employed. Other methods may cause damage
to the thermometer.
With the thermometer in an up right position gradually immerse ONLY half
of the bulb in a solution of solid CO²(Dry-Ice) and alcohol so that
the mercury column retreats slowly into the bulb. Do not cool the stem
or mercury column. Keep the bulb in the solution until the main column
as well as the separated portion retreats into the bulb. Remove and swing
thermometer in short arc forcing all the mercury into the bulb.
Most mercury thermometers can be reunited using this method
regardless of range (with the exception of deep immersion thermometers)
provided ONLY HALF THE BULB is immersed in the CO²
- Do not touch the bulb until it has warmed sufficiently
for the mercury to emerge from the bulb into the capillary.
- Never subject the stem or mercury column to the CO²
solution as it will freeze the mercury column in the capillary and may
cause bulb to fracture.
This method applies to thermometers with a maximum range of 260° C
or 500° F, equipped with expansion chambers sufficiently large enough
to accommodate the separation plus a portion of the main column. Immerse
as much of the bulb and stem as possible in a large beaker containing
a liquid whose flash point is well above the highest indication of the
thermometer being reunited. Heat the beaker stirring the liquid with the
thermometer until the separation and a portion of the main column enters
the chamber. Tap the thermometer in the palm of a gloved hand to aid in
reuniting the column. Allow the thermometer to cool slowly.
- Never use open flame on bulb.
- Never fill expansion chamber more than 2/3 full.
- Make certain Flash Point of liquid is well above the
highest temperature indicated on the thermometer.
- Thermometers whose range exceed 260° C or 500°
F CAN NOT be reunited using heat without damaging the instrument.