Dear Steve,
If this helps - I can only agree with Paul Dennis's comments.  We use similar reaction vessels
and Louwers-Hapert stopcocks with a very sparing amount of Apiezon grease and find no
problems whatsoever.  Normally we react for 6hours after evacuating the vessels and acid
overnight.

Best wishes
Paul

On Wed, 2 Jul 1997 13:19:11 -0500 Steve Nelson wrote:

> From: Steve Nelson <[log in to unmask]>
> Date: Wed, 2 Jul 1997 13:19:11 -0500
> Subject: high residual gas pressure
> To: [log in to unmask]
>
> 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
> *********************************




Paul Kennedy
Stable Isotope Laboratory
Marine Science Laboratories
University of Wales
Menai Bridge
Gwynedd LL59 5EY
U.K.
email [log in to unmask]
Tel ++ 44 (0)1248 351151 exn 2847
Fax ++ 44 (0)1248 716367