[pH] n [G, fr. Potenz power + H (symbol for hydrogen)] (1909): a measure of acidity and alkalinity of a solution that is a number on a scale on which a value of
7. represents neutrality and lower numbers indicate increasing acidity and higher numbers increasing alkalinity and on which each unit of change represents a tenfold change in acidity or alkalinity and that is the negative logarithm of the effective hydrogen-ion concentration or hydrogen-ion activity in gram equivalents per liter of the solution