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Subject: Alkaline reserve

Alkaline reserve

From: Ellen McCrady <whenry>
Date: Sunday, August 12, 1990
The subject of easy ways to measure alkaline reserve has concerned
George Kelly (former chemist, Library of Congress) for years, because he
wanted people to be able to measure it themselves.  The easiest way that
he or anyone has found is back titration.  He said, in a letter to the
editor in the Alkaline Paper Advocate (Dec. 1988), "I think the method
is basically suitable for unsophisticated laboratories... The method is
inherently accurate and precise...."  He discusses possible sources of
error, the choice of pH meter vs methyl red indicator, and other matters
in this long letter.  I reprinted his original article in which he
described the process to the conservation community (Bull. AIC v.13 #1,
1972, p. 16-28, "Practical Aspects of Deacidification") in the April
issue of APA.  In this paper he discusses solubility and other related
matters, and gives the formula for calculating alkaline reserve in
milliequivalents per kg.  The method does call for the use of a blender
and some lab glassware, and certain simple chemicals.  A working pH
meter is not necessary if you have methyl red.  (I say "working" because
so many conservation labs have trouble keeping theirs in working
condition.)  The method is simple enough that it was the one we were
taught in the lab course for preservation administrators at Columbia.  I
have everything here in my workroom to do it, but have somehow have
never found the time.  A similar method is specified in the four ASTM
paper permanence standards (see, for instance, D 3290).  Standards have
to use the simplest methods that will give reliable results, to ensure
that both supplier and purchaser of materials will be able to perform
the tests and resolve disagreements about quality of the goods

I can testify that simply putting acid on the paper and watching it to
see if it bubbles is not a reliable method.  Some paper bubbles like
mad, and other paper that we know contains considerable CaCO3 just sits
there.  George Kelly gives some reasons why this might be so in the
aforementioned letter, and I have a hypothesis of my own.  Whatever it
is that keeps the CaCO3 from interacting with acid in the intact paper
at the workbench probably also keeps it from interacting with the acidic
gases it is supposed to be protecting the paper fiber against.  Could it
be the size?  It does latch onto the filler as well as the fiber. But
that is another matter.  George Kelly says that disintegrating the paper
into a slurry is necessary to make sure your acid is able to get at the
CaCO3 and I believe him.  Any CaCO3 that is still not affected by the
acid after disintegration would probably not be effective as an alkaline
buffer anyhow.

                  Conservation DistList Instance 4:10
                  Distributed: Friday, August 17, 1990
                        Message Id: cdl-4-10-004
Received on Sunday, 12 August, 1990

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