Fifty c.c. of the sample are titrated with decinormal soda or baryta, using phenolphthalein solution as indicator.

Fixed Acidity

Another portion of 50 c.c. is evaporated in a beaker to near dryness over a steam-bath, about 25 c.c. of distilled water added, and the solution again evaporated The residue is then dissolved in about 25 c.c. of cold, recently boiled, distilled water and titrated with decinormal soda or baryta as before. The difference between the fixed acid so ascertained and the value obtained for the total acidity is a measure of the volatile acid. Both are expressed in terms of acetic acid.