The equilibrium constant $K_{\text{H}n}$ for the addition of the $n$th proton to a charged or uncharged ligand. The cumulative protonation constant, ${\beta }_{\text{H}n}$, is the equilibrium constant for the formation of H_nL from $n$ H⁺ and L. The same equilibrium constant may be described in several ways, depending on how the ligand, L, or the acid, has been defined.