_Procedure._—Modify the method for free mineral acids by titrating the
water at boiling temperature in the presence of phenolphthalein
indicator. The acidity due to free mineral acids and sulfates of iron
and aluminium, expressed in terms of calcium carbonate, is equal to the
number of cubic centimeters of N/50 sodium carbonate used multiplied by
20 if 50 cc. of the sample was used, or by 10 if 100 cc. was used.
The acidity due to sulfates of iron and aluminium is equal to the
acidity due to mineral acids and sulfates minus the acidity due to
mineral acids. The acidity due to ferrous and ferric sulfate can be
calculated from the determined amount of these salts (pp. 43–48). The
acidity due to aluminium sulfate is equal to the acidity due to total
acid sulfates minus that due to iron sulfates.
Acidity shall be reported in parts per million of calcium carbonate
(CaCO_{3}). Sulfate (SO_{4}) equals parts per million of calcium
carbonate multiplied by 0.96.
Carbon dioxide (CO_{2}) equals parts per million of calcium carbonate
multiplied by 0.44.