_Procedure._—Add 2 drops of methyl orange indicator to 50 or 100 cc. of
the sample in a white porcelain casserole or an Erlenmeyer flask over a
white surface. Add N/50 sodium carbonate from a burette until the pink
coloration of the solution disappears. The acidity due to free mineral
acids, 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.