Ask A Scientist© General Science Archive

name        chad
status      other
age         20s

Question -  In reference to Mercury thermometers vs. Spirit filled
thermometers - I was wondering if you have any info on accuracy of the
Spirit filled vs. accuracy of Mercury filled thermometers. Thanks.ral

Chad,

In most applicarions for which they are designed, the spirit filled
thermometers are adequate. As a science teacher, I was pleased to phase out
the mercury filled thermometers because of breakage and the hopelessness of
ever getting all the mercury cleaned up. I suspect most older science lab
rooms are heavily contaminated with mercury from years of (instructor and)
student "accidents.".

For precision work, mercury thermometers are sometimes still required.
Nevertheless, as technologies improve, they will doubtless be replaced
whenever possile by electronic thermometers.

Regards,

ProfHoff
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The non-mercury thermometers are accurate enough that we use them and
trust them in a research lab at Yale. They also save a huge amount of
trouble since thermometers do get broken occasionally, and for a mercury
thermometer, the biohazard cleanup team shows up in spacesuits with a
glorified vacuum cleaner especially for mercury (no kidding!).

Christine Ticknor
Ph.D. candidate
Yale University
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There is a trade off. Spirit thermometers have higher resolution over
their range of utility because the density of the fluid is much less than
mercury and the coefficient of expansion of the fluid, that is, change in
volume/change in temperature is larger than mercury [I think]. You can check
this out from the Handbook of Chemistry and Physics, or some other reference
book. So since the bore of the capillary is constant (or should be) this
translates into a larger change in length of fluid per degree change in
temperature.

The limitation is that the range of utility of the spirit thermometer is
much less than the mercury thermometer.

If you are looking to measure temperature you should look into thermocouple-
type thermometers. They are fairly inexpensive, reasonably accurate, have a
wide range of utility, and don't have a disposal problem like mercury
thermometers if/when they break.

Vince Calder
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