This International Standard specifies a method for the determination of the Kappa number of pulp. The Kappa number is an indication of the lignin content or bleachability of pulp. This International Standard is applicable to all kinds of chemical pulps and semi-chemical pulps within the Kappa number range 1 to 100. For pulps with a Kappa number exceeding 100, use the chlorine-consumption procedure (ISO 3260) to describe the degree of delignification.To achieve the greatest precision and accuracy, the sample size should be adjusted so that the consumption of permanganate falls between 20 % and 60 % of the amount added. NOTE There is no general and unambiguous relationship between the Kappa number and the lignin content of pulp. The relationship varies according to the wood species and delignification procedure. All compounds oxidized by KMnO4, not only lignin, will increase the consumption of KMnO4, and thereby increase the Kappa number (see [7]). If the Kappa number is to be used to derive an index of pulp lignin content, specific relationships will have to be developed for each pulp type.