Date: Around 1999
Hello, I am an educator at the Science Museum of
Minnesota. I have been
asked to find out what temperature mercury freezes at and is no longer
accurate as a thermometer. I know that the freezing point of mercury is -38F,
but are thermometers specially insulated or treated so that they are
accurate to a lower
Please help me find this information! I have been looking for
I don't know what kind of thermometer you used, but you could try
something which resembles a thermocouple. The wires are generally
available in a physics laboratory. Once you have the wire, two
strands-of different metal. Then calibrate the thermocouple with a good
Voltemeter, you will need to read millivolts. Calibrate at room temp and
a very low temp (liquid nitrogen). Room temp should provide zero voltage
and liquid nitrogen some millivolts.
If you are desperate, there are some really good physicists at the
University of Minnesota, Dahlberg or Goldman. Have one of their graduate
students give you a hand. It will take 5 minutes.
Thermometers to measure temperatures below the freezing point of mnercury
use some other measuring technique. Thermocouples are popular for lower
temperatures, as are spirit thermometers that use alcohol instead of
mercury. The thermometers I use in lab for measuring low (around dry ice
temperatures) use pentane as the liquid instead of mercury. These
thermometers are good only below room temperature.
Richard Barrans Jr., Ph.D.
Chemical Separations Group
Argonne National Laboratory
A mercury thermometer will probably lose accuracy somewhat above
the freezing point, because as one approaches the phase
transition from liquid to solid, one loses the linear dependence
of the column length on temperature. This is because the
expansion coefficient of materials is generally temperature-
dependent. I have no data handy on the specific temperature
dependence of mercury, unfortunately. You might try
consulting tables of thermodynamic data of the elements,
which might give the density as a function of temperature.
From this you could plot the molar volume as a function of
temperature, and see whether the plot is linear or nonlinear
over the temperature range you are interested in.
Thermometers are advertised by their manufacturer to work only
within specified temperature ranges, and outside of that range
they may no longer work with the same (linear) calibration.
I hope this is helpful. All the best,
Prof. Robert Topper
Dept of Chemistry
The Cooper Union
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Update: June 2012