Experiment 1. Temperature and Pressure Calibration

1
Experiment 1. Temperature and Pressure
Calibration
Temperature measurement tips are illustrated
here for one of the setups at Station 4. The
reference thermometer in this case is an
electronic device which measures to the nearest
0.1 and is stated to be accurate to within
0.2. Make sure that the thermistor (connected
to wires) and the reference thermometer are
immersed to a sufficient depth but not so deep
that they interfere with the stir bar. For this
electronic thermometer, position the tip about an
inch below the tip of the thermistor.
2
2
Proper adjustment of the stirring speed is
important for achieving good mixing, leading to
thermal equilibrium.
It is easiest to collect data working down in T,
but you should also collect some points with the
bath warming up. To cool the bath, add small
chunks of dry ice (at Stations 4 and 6) or ice
(Station 3). Dont add too much dry ice!
Wait until all solid is gone before attempting
a measurement You do NOT have thermal
equilibrium if solid is present!
3
3
For the calibration of the Baratron pressure
gauge, you will use an open-ended mercury
manometer, so you will have to measure the levels
of the meniscus on both sides. Using a white
card as an aid, you should be able to measure
each level to the nearest 1/3 mm.
Take care not to subject the manometer to sudden
large changes in pressure Guess what happens to
people who spill mercury in the laboratory!

4
4
The open end of the manometer is at atmospheric
pressure, which you will measure precisely using
the mercury barometer in the lab. This
instrument is equipped with a vernier scale for
precise measurement. For example, the vernier
depicted here is reading 41.4 mm (actually 741.4
Torr, the 7 being suppressed). The readings
of this instrument and the manometer will have to
be corrected for thermal expansion of Hg, as
discussed in the writeup.
.4
41
5
5
The LabWorks Interface used in this experiment
is also used in Experiments 3, 4, and 6 to record
temperature (and in Expt. 4, pressure) directly
into a computer file, as a function of time. The
computers will usually be ready to go, but if
not, you can find the program easily and start
it. The program logs data into a file, so that
in case of a crash, all is not lost. However,
this file is overwritten each time you start
logging data, so you will need to select Save
each time you stop logging. The program will
store up to 2000 points before it stops on its
own, but you can stop it at any time.