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Subject: Silica gel

Silica gel

From: Gillian Noseworthy <gilliano>
Date: Monday, January 12, 1998
I've been trying to do the calculations for the required amount of
silica gel for several exhibit cases.  Using the literature, (CCI
Tech. Bull. #10, Nathan Stolow's article in "Care of Collections"
etc.), I understand the formulas and what is needed.  My problem is
the EMC (Equilibrium Moisture Content) that is given in both
articles are for particular grades of silica gel, none of which are
grade 44 (Davison Type VI, mesh 3-8) indicating type, which I am
working with.

I have called Fischer Scientific (locally) and they had no
information on the isotherm curve for this grade other than the
"general EMC curve for silica gel".  Perhaps grade 44 is the same as
41? The only info I have gotten from a catalogue is that it has a
minimum 31% absorption at 80% rH, which appears to correspond to
grades 41 and/or 42 in CCI's tech bull #10 p.4.  I know the EMC can
be calculated based on testing samples from the cases, but the cases
are difficult to access, and it would be nice to have the info
(despite the fact it omits case leakage and ambient temperature
etc).  So, does anyone know where I can find out the information on
isotherm (EMC) curves for this grade of gel?

This same question also applies to activated carbon being placed in
cases.  Since this is not an indicating does one know
when it is exhausted?  Are there similar formulas for carbon as for
silica gel? Thanks for any info,

Gillian Noseworthy
Conservation, Museum of Anthropology, UBC
+1 604 822 2981

                  Conservation DistList Instance 11:60
                 Distributed: Tuesday, January 13, 1998
                       Message Id: cdl-11-60-004
Received on Monday, 12 January, 1998

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