The Cox-Yates equation is an example of an "excess" type of these, and is a modification of the Burnett-Olsen function, which is itself is a more general form of one of these.  One of these developed by Stevens, Yates, and Katrizky is based on primary amides, and experimental data on one developed by Stewart shows that the activity coefficient of the media used to measure the namesake property is based on the dielectric constant. The most commonly used one employs a set 
The Cox-Yates equation is an example of an "excess" type of these, and is a modification of the Burnett-Olsen function, which is itself is a more general form of one of these.  One of these developed by Stevens, Yates, and Katrizky is based on primary amides, and experimental data on one developed by Stewart shows that the activity coefficient of the media used to measure the namesake property is based on the dielectric constant. The most commonly used one employs a set of nitroaniline references and was developed by Louis ? Hammett. They are measured using similar indicators of varying strengths and their development accounted for compounds with a stronger proton donating ability than H2SO4. FTP, name these functions which improve on the measures approximated in the Henderson-Hasselbalch equation and the pH scale and encompass all functions measuring "basicity".
The Cox-Yates equation is an example of an "excess" type of these, and is a modification of the Burnett-Olsen function, which is itself is a more general form of one of these.  
{acidity} functions (3) [prompt on “{basicity functions}” before mention since the {term} is {uncommon}]