Dear Listmembers,

        Once again I hope to enlist your help.  I have built a conventional
carbonate line and all seems to be working well now except one item--the
reaction vessels--which seem to contain high residual gas pressures [about
40 microns upon expansion into the manifold].  The pressures are high
enough that the gas transfer rates are slow.  It takes 7-8 minutes to
freeze down 100 micromoles of CO2 and clearly that is too long.  This is
after rough pumping overnight on the acid/sample and then pumping for at
least a couple of hours with the diffusion pump and a cold trap before
reaction.  I have been letting samples react overnight.  Once the CO2 is
trapped and the residual gas is pumped away, the CO2 will freeze again very
rapidly if I re-expand it.

        My two legged reaction vessel design was copied from a colleage.
The upper half contains the teflon/o-ring stopcock and the lower half
contains the two legs for reagent and sample.  They are joined with a ACE
o-ring connection and a clamp rather than a ground glass fitting.

        I ran blank vessels to determine whether the residual gas was
related to the reagent or the reaction.  I rough pumped on the vessels
overnight and then with the diffusion pump and a cold trap, then I closed
the stopcocks.  I left the vessels on the manifold but let them sit
overnight [assuming the problem is not in the stopcocks].  I also torched
the bottom of the vessels before closing the stopcocks.  Overnight a
residual pressure of about 40 microns resulted.  Hence, the source of the
residual gas appears to be the reaction vessel itself.

        It seems to me that if the problem were leakage, that it would be
unlikely that all of the vessels would produce such similar residual
pressures or leak the same amount.  Any ideas as to the cause or a possible
solution would be appreciated.  I've struggled with this for quite some
time now.

********************************
Steve Nelson
Dept. of Geology
673 WIDB
Brigham Young University
Provo. Utah  84602

voice:  1-801-378-8688
FAX:  1-801-378-8143

"INTEL INSIDE" is a warning label
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