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a measure of the concentration of hydrogen ions in a solution, which shows how acid or alkaline it is

COMMENT: The pH value is shown as a number. A value of 7 is neutral; lower values indicate increasing acidity and higher values increasing alkalinity. The maximum reading is pH10, which is completely alkaline. Paper should be less acid (i.e. should have a pH value of 7 or more) if it is to be used for books which are likely to have a long life. Acid-free paper (with a very high pH value) is used in libraries to wrap and protect valuable books and manuscripts. Newsprint has a low pH value (5 or less) and so ages rapidly. The glues used in binding should also be alkaline, with a pH value of 6 or more.



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