Shake 12.25 grams of the sample in a 150 cc. bottle with 75 cc. of 95
per cent alcohol for ten minutes. Run a blank. Filter rapidly both
sample and blank and wash rapidly with alcohol sufficient to make 100
cc. of filtrate. Titrate with N/20 sodium hydroxide in presence of
phenolphthalein and subtract the result of titrating the blank from that
of titrating the solution of the sample. The percentage of acidity,
expressed as sulfuric acid (H_{2}SO_{4}), is equal to 0.02 times the
number of cubic centimeters of sodium hydroxide used.