It is well known that cellulose, which forms the fibrous constituent of paper is a polymeric substance and is liable to degradation both by acids and by alkalis. Strong acids cause the links in the polymer chain to break irreversibly and thus eventually reduce the strength of the fibre and of the paper of which it is made. Strong alkalis increase the ease with which cellulose is oxidised with consequent loss of the strength of the fibre. W. J. Barrow 1 has proved conclusively that acid is commonly present in paper, either from alum used in the size, from atmospheric impurities or from ink absorbed and retained by the paper, and that this acidity is one of the major causes, if not the prime cause, of paper degradation. He has been responsible for the pioneer work in developing methods of deacidifying paper. The presence of carbon dioxide in the atmosphere acts as a fairly effective counter to strong alkalis and the problem of excessive alkalinity in paper rarely arises. Barrow suggests that permanent paper should have a pH6topH8.It is convenient here to explain what is meant by the terms »strong« and »weak« when these are used in a chemical sense and applied to acids and alkalis. These terms are not to be confused with those describing the order of amount present for which the correct terms are »concentrated« and »dilute«. A »strong« acid or alkali is one which is completely ionised in solution to produce respectively hydrogen and hydroxyl ions. A »weak« acid or alkali is one which ionizes in solution to a limited extent and produces a much smaller number of hydrogen or hydroxyl ions in equilibrium with the unionized portion of the acid or base. This theoretical treatment applies to salts too. A water soluble salt, when dissolved in water will ionize completely and if both the acid and alkali moieties are strong, the solution will be neutral as is the case with common salt. If, however, the acid is strong and the alkali is weak, the salt will still ionize completely but the alkali moiety will establish equilibrium with the water present by abstracting hydroxyl ions leaving an overall excess of hydrogen ions to make the solution acid. An analogous reaction occurs with the salt of a weak acid and strong alkali, but in this case the solution will be alkaline.
This paper discusses the characteristics of the commoner classes of writing materials and textiles deriving from ancient and more recent historical sources and the problems they present for 14C dating. The materials under consideration are, firstly, paper in various forms, parchment, and vellum (ancient papyrus, which poses different kinds of dating problems, is not considered) and secondly, fabrics such as linen, cotton, and woolen textiles, to which, from the dating point of view, similar technical considerations apply. Our main concern is with problems associated with the dating of paper.
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