Packaging and storage
Preserve in well-closed containers.
Loss on ignition
733
Transfer about 1 g, previously dried and accurately weighed, to a tared platinum or porcelain crucible, and ignite at 980 ± 25

for 1 hour: it loses not more than 2.0% of its weight.
Acid-soluble substances
Digest 10.0 g with 50 mL of 0.5 N hydrochloric acid at 70

for 15 minutes, and filter. Wash the residue, adding the washings to the filtrate, to obtain a total volume of 100 mL. Evaporate at 110

in a tared porcelain dish to dryness: the weight of the dried residue so obtained does not exceed 200 mg (2.0%).
Water-soluble substances
Place 12.5 g in a 500-mL conical flask, add 250 mL of water, and shake for 2 hours at room temperature. Filter with the aid of vacuum, and again filter if necessary to obtain a clear filtrate. Evaporate in a tared platinum or porcelain dish, and dry at 110

: the weight of the residue does not exceed 25 mg (0.2%).
Leachable arsenic
Transfer 10.0 g to a 250-mL beaker, add 50 mL of 0.5 N hydrochloric acid, cover with a watch glass, and heat at 70

for 15 minutes. Cool, and decant through a Whatman No. 3 filter paper into a 100-mL volumetric flask. Wash the slurry with three 10-mL portions of water, preheated to 70

, dilute with water to volume, and mix: a 3.0-mL portion of this solution meets the requirements under
Arsenic,
Method I
211
. The limit is 0.001%.
Leachable lead
A 10.0-mL portion of the solution prepared in the test for
Leachable arsenic meets the requirements under
Lead
251
, 10 mL of
Diluted Standard Lead Solution being used for the control. The limit is 0.001%.
Limit of nonsiliceous substances
Transfer about 200 mg, accurately weighed, to a tared platinum crucible, add 5 mL of hydrofluoric acid and 2 drops of dilute sulfuric acid (1 in 2), and evaporate gently to dryness. Cool, add 5 mL of hydrofluoric acid, evaporate again to dryness, and ignite to constant weight: the weight of the residue so obtained does not exceed 50 mg.