21. The activity coefficient depends on the ionic strength of the solution in which the potentiometric measurements are made. 22. P _ { i } may be calculated according to Raoult's Law using appropriate activity coefficients . 23. Expressions were derived for the variation of single-ion activity coefficients as a function of ionic strength. 24. Sometimes activity coefficients can be calculated using, for example, Pitzer equations or Specific ion interaction theory. 25. The expressions show that at \ alpha _ { 12 } = 0 the limiting activity coefficients are equal. 26. Because of this the Pitzer equations provide for more precise modelling of mean activity coefficient data and equilibrium constants. 27. Activities can be calculated from concentrations if the activity coefficient are known, but this is rarely the case. 28. While at MIT he began his career by developing one of the first computer-based Activity coefficient Equations. 29. For uncharged species, the activity coefficient " ? " 0 mostly follows a salting-out model: 30. With & gamma; i as the activity coefficient calculated by the Debye H�ckel equation and / or Davies equation.
