Packaging and storage—
Preserve in tight containers.
Identification—
A solution (1 in 25) responds to the tests for
Sodium 
191
.
Insoluble substances and organic matter—
A solution (1 in 20) is complete, clear, and colorless to slightly colored.
Potassium—
Acidify 5 mL of a solution (1 in 20) with 6 N acetic acid, then add 5 drops of
sodium cobaltinitrite TS: no precipitate is formed.
Heavy metals 231—
Dissolve 0.67 g in a mixture of 5 mL of water and 7 mL of 3 N hydrochloric acid. Heat to boiling, cool, and dilute with water to 25 mL: the limit is 0.003%.
Assay—
Dissolve about 1.5 g of Sodium Hydroxide, accurately weighed, in about 40 mL of carbon dioxide-free water. Cool the solution to room temperature, add phenolphthalein TS, and titrate with 1 N sulfuric acid VS. At the discharge of the pink color of the indicator, record the volume of acid solution required, add
methyl orange TS, and continue the titration until a persistent pink color is produced. Each mL of 1 N sulfuric acid is equivalent to 40.00 mg of total alkali, calculated as NaOH, and each mL of acid consumed in the titration with methyl orange is equivalent to 106.0 mg of Na
2CO
3.
