该方法描述了一种可用于测定木材和所有等级未漂白纸浆中酸不溶木质素的程序。在半漂白纸浆中，木质素含量不应小于约1%，以提供足够量的木质素（约20 mg），以便准确称重。该方法不适用于仅含有少量木质素的漂白纸浆。部分木质素在试验过程中溶解在酸性溶液中，不包括在试验结果中。在针叶林和硫酸盐浆中，可溶性木质素的含量很小，约为0.2%到0.5%。在硬木（落叶木）、非木材纤维和亚硫酸盐纸浆中，可溶性木质素的含量约为3%至5%。在半漂白浆中，可溶性木质素约占木质素总量的一半或更多。注1:在过滤掉不溶性木质素后，可通过基于紫外辐射吸收的分光光度法在溶液中测定酸溶性木质素。 最常用的波长是205 nm（1）。纸浆中的总木质素含量可通过基于木质素氯化（TAPPI T 253 Hypo值纸浆-1998年撤销的方法）或木质素氧化（TAPPI T 236 Kappa值纸浆）的快速间接方法进行相当接近的估算。

This method describes a procedure which can be applied to the determination of acid- insoluble lignin in wood and in all grades of unbleached pulps. In semi-bleached pulp the lignin content should not be less than about 1% to provide a sufficient amount of lignin, about 20 mg, for an accurate weighing. The method is not applicable to bleached pulps containing only small amounts of lignin.Some of the lignin dissolves in acid solution during the test and is not included in the test result. In softwoods (coniferous woods) and in sulfate pulps, the amount of soluble lignin is small, about 0.2 to 0.5%. In hardwoods (deciduous woods), non-wood fibers, and in sulfite pulps, the content of soluble lignin is about 3 to 5%. In semi-bleached pulps, soluble lignin could amount to about one-half or more of the total lignin content.NOTE 1: The acid-soluble lignin can be determined in a solution, after filtering off the insoluble lignin, by a spectrophotometric method based on absorption of ultraviolet radiation. The most often used wavelength is 205 nm (1).The total lignin content in pulps can be estimated fairly closely by rapid, indirect methods based on chlorination of the lignin (TAPPI T 253 Hypo Number of Pulp - method withdrawn in 1998) or oxidation of the lignin (TAPPI T 236 Kappa Number of Pulp).