Cox–Yates equation

A modification of the Bunnett–Olsen equation of the form:
is the activity function
for an arbitrary reference base. The function
is called the excess acidity because it gives a measure of the difference between the acidity of a solution and that of an ideal solution of the same concentration. In practice
and

.

Source:

PAC, 1994, *66*, 1101*
(Glossary of terms used in physical organic chemistry.)
*