This paper provides an account of early historical developments in the characterization and quantification of acidity, which may be considered preliminary steps leading to the measurement of acidity. In this “pre-history” of acidity measurement, emphasis is laid on the relative independence of the rich empirical knowledge about acids from theories of acidity. Many attempts were made to compare and assess the strengths of various acids, based on concrete laboratory operations. However, at least until the arrival of the pH measure, the quantification attempts failed to produce anything qualifying as a measurement scale of a recognizable type. It is doubtful whether even pH qualifies as a true measure of acidity, when the full meaning of acidity is taken into account.

In only few sections of chemistry there appears a succession of such opposing and contradictory views as in those about acid, alkali and salt (Kopp (1845), p. 1, our translation).