Ill 1335 with sodium acetate, whose hydrogen-ion concentration is 3.2 X 10 "8 in a tenth molar solution, it would assume a position much nearer the strong nitric acid than the weak acetic acid. Such an approximation would place it near sulfuric acid but below it. Summary 1. The presence of disodium dihydrogen pyrophosphate is given as an explanation for the acidity of solutions of "Graham's salt" and solutions of other sodium metaphosphates prepared by heating monosodium orthophosphate when they are not purified by repeated crystallizations from water.2. The monometaphosphoric acid is near but below sulfuric acid with respect to its activity.