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Our department has a bunch of Winsco (Wabash Instrument Corp.)
gas bulb things, you know, the copper bulb attached to an
"absolute pressure" gauge for testing the relation between
pressure and temperature for an ideal gas (or for defining
a temperature scale based on an ideal gas). What bothers me
is this: We're at 4700' above sea level, where the pressure
should be about 15% less than a standard atmosphere, and yet
all 10 of these things are reading between 760 and 780 mmHg
when the valves are wide open. I tried the experiment, immersing
it in four different temperature baths, with three different
amounts of air in the bulb, and got three nice straight lines
that intersect at about -280 Celsius and +165 mmHg. Thus, I'm
pretty sure that the gauges are off by an additive constant
of roughly 130-160 mmHg. I'm wondering how they could all have
gotten off by this amount. As far as I know they've never been
used, and I can see no way of opening them up and changing the
calibration. I suppose it's possible that years ago, some well-
meaning technician popped all the covers off and twisted the
needles on the dials, but I doubt it. Is anyone out there
familiar enough with this apparatus to tell me how to recalibrate
it? Thanks.
Dan Schroeder
Weber State University
dschroeder@cc.weber.edu