In the State of New York, the legal standard for vinegar is 4·5 of absolute acetic acid, and, in the case of cider vinegar, the proportion of total solids must not fall below 2 per cent. In Massachusetts, also, the acidity must be equivalent to 4½ per cent. of acetic acid, and cider vinegar must contain, at least, 2 per cent. of solid matter. The English standard of strength is 3 per cent. of acetic acid. _Analysis._--For the requirements of the United States Customs Service, the only estimations ordinarily made are the specific gravity, and a determination of the acidity. The former is accomplished by means of the specific gravity bottle; the latter, by placing 10 c.c. of the sample in a beaker, adding about 30 c.c. of water, then a few drops of an alcoholic solution of phenol-phthaleïn (to serve as the indicator), and titrating with a normal alkali-solution; the number of c.c. used divided by 10 and multiplied by 48, gives the amount, in grains, of potassium bicarbonate required to neutralise one troy ounce of the vinegar. In the presence of sulphuric acid, it is necessary to distil a measured quantity of the sample almost to dryness and titrate the distillate, it being assumed that 80 per cent. of the total acetic acid present passes over. The determination of the extract or solid residue in vinegar is executed in the same manner as described under beer and wine. Several tests have been suggested for the detection of the presence of free sulphuric acid. The usual reagent--barium chloride--is not well adapted to the direct determination of this acid, since sulphates, which are as readily precipitated as the free acid, may also be present. The following methods may be employed:-- 1. A piece of cane sugar is moistened with a small quantity of the sample and exposed to the heat of the water-bath for some time, when, in presence of free sulphuric acid, the residue will become more or less carbonised, according to the proportion of acid present. 2. Five centigrammes of pulverised starch are dissolved in a decilitre of the sample by boiling, and after the liquid has become completely cooled, a few drops of iodine solution are added. Dilute acetic acid does not affect starch, and if the sample is pure, a blue coloration will be produced; if, however, but a minute quantity of sulphuric or other mineral acid is present, the starch is converted into dextrine, and the addition of iodine fails to cause the blue coloration. 3. According to Hilger,[133] if two drops of a very dilute solution of methyl aniline violet (0·1 to 100) are added to about 25 c.c. of pure vinegar no change of colour takes place; whereas, in the presence of 0·2 per cent. of mineral acid, a bluish coloration is produced; in case the proportion of acid reaches 1 per cent. the liquid acquires a greenish tint.