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Re: Boiling

At 11:17 AM -0700 3/10/01, Jim Green wrote:
>Here is my collated report:

In 1741 Anders Celsius introduced his version of a temperature scale -- The
scale was defined with the ice point at 100 and the steam point at 0
degrees. He called it the centigrade scale because of the 100 degrees in
the definition. After his death the two points were reversed. In 1948 the
name of the scale was changed to Celsius in his honor. The change was in
view of the fact that the scale had nothing to do with 1/100 of the angular
measure of a grad.

In 1954 the Celsius scale was _re-defined_ to use the Triple Point of
water. This point was defined as 273,16 K exactly -- with the idea in mind
that the ice point would then be close to 0 C and the steam point would be
close to 100 C but alas not exactly. And the Celsius scale was defined to
be offset from the Kelvin scale by exactly 273.15. Thus the TP is exactly
0.01 C.

And experiment shows the ice point to be 0.0000 +-0.0001 and the steam
point to be 99.975 C

If the TP had been defined with more precision, the steam point could have
>been closer to 100.

We see then that we do not use the Celsius scale today -- but close -- yet
>we still call it thus.

>But the answers to my questions are 99.975 C and 1954

Because the boiling point is so close to 100 and the freezing so
close to 0, I doubt this information will make much practical
difference in the lives of my general education students.

But it is, nonetheless, very interesting trivia, and I will
definitely save this post. I'll probably even forward it to my
students (with your permission, I hope, Jim). Thanks, Jim, for the
very clear summary of an interesting topic. I think that as physics
teachers we at least ought to be _aware_ that the two temperatures
are not 0 and 100 exactly, and maybe inform our students, at least in
passing.

Do our physics texts contain this information, or do we all have to
go to PChem books to find this?

Larry