Kappa number
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The Kappa number measures the amount of bleach required during digestion of wood pulp (part of the process of making paper) in order to obtain a given degree of whiteness. Since the amount of bleach needed is related to the lignin content of the pulp, the Kappa number can be used to monitor the effectiveness of the lignin-extraction process. The number is in the range of 10-70 for most types of wood and is established by measuring the amount of a standard potassium permanganate solution that is absorbed by the pulp being considered.