Pat Naughtin wrote:
....
I'm not where I can check your dates and the details, Pat, so I'll skip
that part except to say that you seem to have the gist of it. The IUPAC
apparently couldn't sell 100 kPa as the standard atmosphere so they
called that the standard pressure and designated it to be part of STP.
Of course, this is only a voluntary standard and its jurisdiction is
only in the chemistry community. The IUPAP apparently doesn't care to
get involved in such "standards" except the standard atmosphere
promulgated by CODATA, I suppose. Physicists tend to just use the actual
values for pressures and temperatures explicitly, in my experience. I
can add that the American Meteorological Society adopts 101.325 kPa as
the standard atmospheric pressure value. But, often times, the altitude
corresponding to 100 kPa is taken as the baseline for many graphs.
No, the value of 760 mmHg was not converted from 30 inches, as far as I
can tell. In fact, the standard value in inches is usually given as
29.92 inHg (back-converted from 760 mmHg).
Oh, and barometers don't measure bars; they measure baros
("baro"="pressure"). But you knew that already and were just tweaking
us. :-)
Jim
> ***
>
> It looks a lot like the CGPM simply converted 760 mm of mercury (mmHg) to
> 101 325 newtons per square metre (with a somewhat dubious precision of six
> significant figures).
>
> In turn, it looks a lot like 760 millimetres of mercury was a casual
> rounding of 30 inches of mercury to a metric measure
> (30 inches x 25.4 mm/inch = 762 millimetres)
>
> Which leaves us with Matthew Zotter's original question, 'What society
> defined standard atmospheric pressure ... '
>
> I suppose that the original meteorologists simply looked at the range of
> pressures on their charts (at sea level) and guessed that 30 inches of
> mercury was somewhere near the middle. If we did the same experiments today
> � with a manometer* calibrated in pascals we would guess that the value
> 100 000 pascals was somewhere near the middle of the range.
>
> Doesn't it take a long while to make a simple change.
>
> Cheers,
>
> Pat Naughtin CAMS
> Geelong, Australia
>
> * I avoided the use of the word barometer because I did not want to get
> embroiled in a discussion about machines that measure bars!
--
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