I had a thermometer using a red spirit column. It had very slow
response. One could freeze a butt off waiting to reach equilibrium.
Then I go a mercury thermometer with a large bulb. In comparison to
the other one, it was a dream to use.

It wouldn't fix the need for "personal" thermometers, but it sounds like
thermal conductivity is the problem with red spirit. If you immersed
the entire thermometer into the environment to measure, you'd get a faster reading.

David A. Smith

I agree that it sounds like a thermal conductivity problem, but I'm
not sure that total immersion will solve anything. The (relatively)
large reservoir of fluid in the bulb may be the culprit, being slow to
equilibrate. It's also possible that the glass sheath of the bulb
area of the spirit thermometer was thicker for some reason. Glass is
a pretty poor conductor of heat.

Thermomoeters for different purposes sometimes specify immersion
depth for which they have been designed or calibrated. In the
organic lab, you can find "total immersion", "15 mm immersion"
(for a small distillation column), "40 mm immersion", etc.
The black line etched around the circumference is usually the
immersion depth. For organic lab, I don't think I ever needed
to be so precise and if I could get one cm of the bulb of a
"total immersion" thermometer in a crowded oil bath, that was
good enough.

When I was doing p-chem, we had a NIST calibrated thermometer
that was probably a couple hundred dollars (cf., less than
ten bucks for a cheapo thermometer.) Intermediately priced,
there are NIST traceable thermometers.






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(Ther Moe) wrote:

Thermomoeters for different purposes sometimes specify immersion
depth for which they have been designed or calibrated. In the
organic lab, you can find "total immersion", "15 mm immersion"
(for a small distillation column), "40 mm immersion", etc.
The black line etched around the circumference is usually the
immersion depth. For organic lab, I don't think I ever needed
to be so precise and if I could get one cm of the bulb of a
"total immersion" thermometer in a crowded oil bath, that was
good enough.

Exactly so. It is a little disturbing how few practicing chemists
seem to be aware of immersion length. However, as you mention, there
is often (or usually, in some disciplines) no need for the extra
degree of accuracy that the immersion length criterion provides.

Still, I don't think any of this has any direct bearing on how quickly
the thermometer equilibrates.

When I was doing p-chem, we had a NIST calibrated thermometer
that was probably a couple hundred dollars (cf., less than
ten bucks for a cheapo thermometer.) Intermediately priced,
there are NIST traceable thermometers.

And there are traceable thermocouple thermometers available. Those
offer thermal mass which is orders of magnitude smaller, with a
correspondingly faster equilibration time.

Steve Turner

Real address contains worldnet instead of spamnet