How do I use a partial immersion thermometer correctly?

Suppose I'm using a 76mm immersion glass thermometer. It's no brainer
that the thermometer is supposed to be dipped to 76mm mark to get a
proper reading, but what temperature should the mercury column above the
immersion line supposed to be?

Example 1: measuring temp of 95.0°C water in a 150mm test tube filled w/
water to 80mm from bottom. The thermometer will be placed in test tube
with the bulb 4mm above the bottom of test tube. There will be 70mm of
glass tubing surrounding the column and water vapor will keep that
portion of column rather hot. The 76mm immersion rule is still being
followed. Will it still give true reading?

Example 2: measuring the temp of cup of coffee inside a 2°C walk-in
refrigerator(80°C up to 76mm line, 2°C atmosphere above 76mm), true
reading or not?


Place total and partial immersion thermometer side by side and leave them
in 25°C air. Will they both give true reading? How about in 105°C sauna
room?

AC/DCdude17 <[Only registered users see links. ]> wrote:


When calibrated, the air temperature is also specified according to the
specification of the thermometer. It's assumed that the column above the
line will be at a constant ambient temperature, usually 20C ( or some other
standard temperature ).

There are "stem correction" tables for correcting some thermometers when using
total and partial thermometers in different environments but, as the correction
can be up to 20C, such misuse is seldom accepted in standard methods. Use the
the correct tool for the job.


No, but them again you are not following the immersion rule, which requires
that the stem above the immersion be held at a specified constant temperature.

The immersion line does not indicate that you have to immerse the thermometer
in liquid to that point, but that the line is where the heating has to cease,
whether vapour, liquid, solid, or a mixture.

That's why there are so many "specialist" types of thermometers - each one is
calibrated according to the agreed specification covering the actual use in
equipment, which will include the depth of immersion, the air temperature,
and position of the bulb. In many distillation methods, the position of the
lower capillary ending is defined by reference to the lowest vapour path out
the sidearm to the condenser ( confused :-) ? ).

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No. The column above the line is not at the calibrated temperature.


As has been noted above, the thermometers will only read true if their
calibration conditions are also satisfied, so that will only occur if
both have the same calibrated temperature, and the ambient is at that
temperature.

Followups set to sci.chem only.

Bruce Hamilton