Exp 14, Ps values from eqn 6, Ps for b.p.

[robert zellmer]

I've received questions from several of you about getting negative
values for Ps from eqn 6 in the manual and what to use for Ps
for the boiling points.  I think this info is in my help file for exp 14
on my web page and it is in the manual (paragraph below
eqn 6).

1) Negative Ps values?  Wrong unit for T.  Remember this

KELVIN, KELVIN, KELVIN

You pretty much always need to use kelvin temp. scale in eqns.
The only time it's really safe to use Celsius is when it's a
delta(T) (change in temp).  This is because the size of the unit
in Celsius and kelvin is the same.

2) You don't need eqn. 6 for the V.P. at the boiling point. A
     substance boils when it's V.P. equals the prevailing atmospheric
     (barometric) pressure for the day.  Thus the b.p. for a liquid is
     different throughout the day as the barometric pressure changes.
     The b.p. is the temperature when the atmospheric pressure is 1 atm
     (760.0 from the manual, use 4 s.f.).

     For the knowns you get the normal b.p. from the CRC.  For your
     unknown you use the barometric pressure you obtained in the lab.

Remember, I have a help file for this exp and an example for
using Excel and the graph for the 3 known compounds.  There
should be two graphs, one with the data for the 3 knowns and
one with the data for your unknown.

Dr. Zellmer
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