2 SOLUTION PROPERTIES

THE PROPERTIES OF DEACIDIFICATION solution relevant to this evaluation are clarity and concentration. Clarity, or freedom from undissolved and extraneous solid matter, is usually measured by visual inspection, what is “clear enough” being a matter of judgment. Concentration can be tested by several less subjective methods. The optimum concentration for a given application is, however, controversial, relating to the amount of alkali left in the treated paper.

Santucci1 noted that a two-percent alkaline reserve, based on studies of well-preserved early volumes, was proposed as early as the 1930s. Both the National Archives2 and the Library of Congress3 have investigated the relationship between concentration of deacidification solutions and alkaline reserve. The Library of Congress recommends a 2–3% deposit of alkali, or 400–600 milli-equivalents in a kilogram of paper. National Archives tests show that a magnesium bicarbonate solution of about 0.1 M concentration is required to produce this reserve in a normal dipping treatment. TheTaylor Hardness test (titration for dissolved magnesium with EDTA) is a convenient test of concentration, which indicates a 0.1 M solution by a minimum of 18 ml of titrant.4

While a more dilute solution may be appropriate in many cases, the capability of generating a water-clear solution of this strength was chosen as a standard for evaluating our system's performance. At the time we began testing, our solutions were normally neither clear nor of optimum concentration.