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The largest single cause
for the failure of precision thermometers in
the lab is the separation of 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 damage the
thermometer.
Cooling
Method...
With the thermometer in an upright position,
gradually immerse only 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 and the separated portion retreat
into the bulb. Remove and swing thermometer in
a 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 the bulb
is immersed in the CO2 and alcohol
solution.
Caution:
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 the bulb to fracture.
Heating
Method...
This method applies to thermometers with a
maximum range of 260°C (500°F) equipped with
expansion chambers sufficiently large to
accommodate the separations 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
enter the chamber. Tap the thermometer in the
palm of gloved hand reuniting the column. Allow
to cool slowly.
Caution:
1
Never use an open flame on the bulb.
2 Never fill the expansion chamber more than
two-thirds full.
3 Make certain the flash point of the liquid is
well above the highest temperature indicated on
the thermometer.
4 Thermometers whose ranges exceed 260°C
(500°F) cannot be reunited using heat without
damaging the instrument.
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1)
Pour your sample into a smooth,
clear
