b. Phenolphthalein indicator solution.
c. Sodium hydroxide-sodium thiosulfate reagent: Dissolve 500 g NaOH and 25 g Na2S2O3.5H2O in ammonia- free distilled water and dilute to 1 liter.
d. Mixed indicator solution: Dis-solve 200 mg methyl red indicator in 100 ml 95% ethyl or isopropyl alcohol. Dissolve 100 mg methylene blue in 50 ml 95% ethyl or isopropyl alcohol. Combine the two solutions. Prepare monthly.
e. Indicating boric acid solution: Dissolve 20 g H3BO3 in ammonia-free distilled water, add 10 ml mixed indicator solution, and dilute to 1 liter. Prepare monthly.
f. Standard sulfuric acid titrant, 0.02 N: Prepare and standardize as directed in Alkalinity, Section 102.3 c. For greatest accuracy, standardize the titrant against an amount of sodium carbonate which has been incorporated in I the indicating boric