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.
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%).
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.
Absorbency—
Proceed as directed for the
Absorbency Test under
Cotton 691: submersion is complete in 5 seconds, and the rayon retains not less than 16 times its weight of water.
