Transcript Mac

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
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). Don’t 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!
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Quic kTime™ and a
Cinepak decompress or
are needed to see this pic ture.
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
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
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.