The ideas of chemists in regard to the nature of the acidity of normal beer have undergone considerable change in the last two or three years. It was formerly considered to be principally due to the presence of lactic acid, with a small quantity of succinic and other acids, but is now considered to bo due, for the greater part, to acid phosphates. Acetic acid is present only to a very limited extent in normal beer, its presence in any considerable quantities being proof of the "souring" of the beer. Ott2 has shown the difficulty of ascertaining the exact point of neutralization in beer, as by the addition of alkali to the acid phosphates the reaction becomes "amphoteric" from the simultaneous formation of both primary and secondary phosphates, and the establishment of the point of neutralization by the reaction with litmus paper is very difficult. No better means of determining acidity in beer has been proposed, however, and I have used the ordinary method of adding standard alkali until a drop placed on neutral litmus paper produces no alteration of color. 50cc are conveniently taken for this determination, freed from carbonic acid and titrated with decinormal alkali. The acidity can be given directly as cubic centimeters of normal alkali required for 100cc. ot beer, or reckoned as lactic acid. The volatile acids, when it is necessary to determine them separately, as in the case of soured beer, may be best estimated by distillation in a current of steam, as described under wine, all methods . for their estimation by difference by evaporating the beer to dryness and titrating the residue having been shown to be faulty.

The Bavarian chemists,3 at their last meeting in 1886, adopted the figure of 3cc. normal alkali for l00cc. beer as a maximum limit for a normal beer.