Casteel−Amis Equation:  Its Extension from Univariate to Multivariate and Its Use as a Two-Parameter Function

The report describes the background of the empirical Casteel−Amis equation and its application to fitting experimental data of conductivity as a function of salt content in electrolytes. It further summarizes the attempts since its publication to extend the equation from a univariate to a multivariate function to include additional variables such as temperature and solvent composition, focusing on that to extend it to a bivariate function of salt content and solvent composition with examples from the solutions of LiPF 6, LiBF 4, LiBOB, Et 4 NPF 6, and Et 4 NBF 4 in propylene carbonate (PC) + diethyl carbonate and in PC + ethylene carbonate and LiClO 4 in PC + acetonitrile. In addition, I discuss, along with experimental data and functional analysis, the validity of using this equation as a two-parameter function in relation to the range of salt content.