Code of Federal Regulations Title 27. Alcohol, Tobacco Products and Firearms § 27.21.102 Caustic soda, liquid

(a) The liquid caustic soda may consist of either 50 percent or 73 percent by weight sodium hydroxide in aqueous solution. The amount of caustic soda used shall be such that each 100 gallons of alcohol will contain not less than 8.76 pounds of sodium hyroxide, anhydrous basis.

(b) Color. A 2 percent solution of the sodium hydroxide in water shall be water-white.

(c) Assay. The sodium hydroxide content of the caustic soda solution shall be determined by the following procedure:

Accurately weigh 2 grams of liquid caustic soda into a 100 mL volumetric flask, dissolve, and dilute to the mark with distilled water at room temperature. Transfer a 25 mL aliquot of the solution to a titration flask, add 10 mL of 1 percent barium chloride solution, 0.2 mL of 1 percent phenolphthalein indicator, and 50 mL of distilled water. Titrate with 0.25 N hydrochloric acid to the disappearance of the pink color. Not less than 25 mL of the hydrochloric acid shall be required to neutralize the sample of diluted 50 percent caustic soda, and not less than 36.5 mL of the hydrochloric acid shall be required to neutralize the sample of diluted 73 percent caustic soda.

One mL of 0.25 N hydrochloric acid equals 0.01 gram of sodium hydroxide (anhydrous).