The Jewett reference, as presented to the list, is incorrect. It does
not matter whether a thermometer is mercury, alcohol, or some other
liquid (like mineral oil, kerosene, pentane). In all certified
thermometers an immersion depth is specified, and this depth is marked
right on the thermometer.
The two most common immersion methods are (1) total immersion and (2) an
immersion of 76 mm (about 3 inches). Other depths are available, but
much less common. In any event, the non-total-immersion thermometers
should have a ring engraved around the stem to indicate the correct
immersion depth
The most common glass thermometer used in chemistry labs has a range
from -10 to 110 Celsius and is 76 mm immersion.
In analytical chemistry one of the lessons for using glass thermometers
is how to make "stem corrections." This correction is necessary if you
want to achieve the stated accuracy of the thermometer, but for some
reason you have to use the thermometer with a different immersion depth
than specified by the manufacturer. Generally this happens if you have
a total immersion thermometer and you have to use it with partial
immersion. If you Google [thermometer + "stem correction"] you will get
about 700 hits explaining this.
I am curious to know if this is one of those things chemists learn, but
physicists do not. I went through both programs in college and learned
about stem corrections in freshman chemistry. For many years I was
department chair, and now I am "Director of Laboratories" for a science
department that includes, biology, chemistry, and physics. This means I
have been purchasing all the thermometers for the department for the
last 20 years or so. I almost always buy 76-mm immersion, but I have to
ask the requesting professor what the intended use is. I've sometimes
had to buy immersion depths longer or shorter than 76 mm. You can go to
a vendor such as Fisher Scientific ( www.fishersci.com ). If you go
there they request a login, but you do not need to, just search on
thermometer and you'll find about 70 mercury, 50 non-mercury, and about
70 digital.
Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu