Waters may have an acid reaction because of the presence of free carbon
dioxide, mineral acids, or some of their salts, especially those of iron
and aluminium.
_Reagents._—1. N/50 sodium carbonate. Dissolve 1.06 grams of anhydrous
sodium carbonate in 1 liter of boiled distilled water that has been
cooled in an atmosphere free from carbon dioxide. Preserve this solution
in bottles of resistant glass protected from the air by tubes filled
with soda-lime. One cc. is equivalent to 1 mg. of CaCO_{3}.
2. N/22 sodium carbonate. Dissolve 2.41 grams of anhydrous sodium
carbonate in 1 liter of boiled distilled water that has been cooled in
an atmosphere free from carbon dioxide. Preserve this solution in
bottles of resistant glass protected from the air by tubes filled with
soda-lime. One cc. is equivalent to 1 mg. of CO_{2}.