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This method describes a rapid procedure (1, 2, 3) for the measurement of the viscosity of 1% cellulose solutions using cupriethylenediamine saturated with cupric hydroxide [Cu(OH)₂] as the solvent. For convenience, this may be referred to as Cu(En)₂ or CED.

This method is the preferred procedure for pulps containing more than 4% lignin; however, many high yield pulps, at levels above 50%, contain sufficient lignin (in excess of 10%) to interfere with the test. The falling ball method may be used over the entire range of bleached and unbleached pulps and is well suited to production control. However, the preferred procedure for pulps with less than 4% lignin, as defined by TAPPI T 222 "Acid-Insoluble Lignin in Wood and Pulp," is TAPPI T 230 "Viscosity of Pulp (Capillary Viscometer Method)," which should be used for referee purposes on these pulps.

This procedure covers preparation of cupriethylenediamine, dissolving the sample, viscometer calibration, and measurement of the viscosity of the sample solution.