» Purified Rayon is a fibrous form of bleached, regenerated cellulose.
Alkalinity or acidity Immerse about 10 g in 100 mL of recently boiled and cooled water, and decant 25-mL portions of the water, with the aid of a glass rod, into each of two dishes. To one portion add 3 drops of phenolphthalein TS, and to the other portion add 1 drop of methyl orange TS: neither portion appears pink when viewed against a white background.
Residue on ignition 281: not more than 1.50%, determined on a 5.0-g test specimen.
Acid-insoluble ash To the residue obtained in the test for Residue on ignition, add 25 mL of 3 N hydrochloric acid, and boil for 5 minutes. Collect the insoluble matter on a tared filtering crucible, wash with hot water, ignite, and weigh: the residue weighs not more than 63.0 mg (1.25%).
Water-soluble substances Proceed as directed in the test for Water-soluble substances under Purified Cotton: the residue weighs not more than 100 mg (1.0%).
Fiber length and absorbency Remove it from its wrappings, and condition it for not less than 4 hours in a standard atmosphere of 65 ± 2% relative humidity at 21 ± 1.1. Determine the Fiber length and Absorbency as follows.
Fiber length Determine the fiber length of Purified Rayon as directed for Fiber Length under Cotton 691: not less than 70.0%, by weight, of the fibers are 19 mm or greater in length, and not more than 5.0%, by weight, of the fibers are 6.3 mm or less in length.