## Cox–Yates equation

https://doi.org/10.1351/goldbook.C01386
A modification of the @[email protected] of the form: $\log _{10}(\frac{[\text{SH}^{+}]}{[\text{S}]})- \log _{10}[\text{H}^{+}] = m^{*}\ X + \text{pK}_{\text{SH}^{+}}$ is the activity function $\log _{10}(\frac{\gamma _{\text{S}}\ \gamma _{\text{H}^{+}}}{\gamma _{\text{SH}^{+}}})$ for an arbitrary reference base. The function $$X$$ is called the @[email protected] because it gives a measure of the difference between the @[email protected] of a solution and that of an ideal solution of the same concentration. In practice $X=- (\mathrm{H}_{0}+\log _{10}[\mathrm{H}^{+}])$ and $m^{*}=1- \mathit{\Phi }$
Source:
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1101 [Terms] [Paper]