At 07:09 AM 1/26/01 -0700, you wrote:
<snip. . .

>For most sample preparations, a better quality fore-pump plus a molecular
>sieve trap or equivalent serves the purpose. If lower pressure is required,
>one can use an oil diffusion pump or a turbomolecular pump.
>Roy Krouse
>

I want to strongly second Roy Krouse's opinion.  When we set up our vacuum
line a few years ago, I chose a turbomolecular pump because of
environmental and health concerns.  With a mercury pump, if the line
suffered a crack or break, the entire thing would have to be disassembled
and cleaned before our glassblower would work on it - a major pain with
lots of down time.

The only drawback, - the turbomolecular pump is a pricey option and may not
be practical for every lab in every setting.  As an added advantage, the
turbomolecular pump offers huge advantages in pumping time over a mercury
diffusion pump, so if processing time is important, there might be some
cost savings there.


Regards,
   -Mark Schurr

*************************************************
Mark R. Schurr, Ph.D., R.P.A    Phone:  (219) 631-7638
Assistant Professor                     FAX:     (219) 631-8209
Department of Anthropology              http://www.nd.edu/~mschurr
University of Notre Dame
Notre Dame, IN  46556 USA