Determinations of the specific rates of solvolysis of 1-adamantyl bromide and 1-adamantyl iodide in 1,1,1,3,3,3-hexafluoro-2-propanol-water mixtures, in conjunction with earlier reported values in 80% ethanol, have led to additional YBr and YI solvent ionizing power values. These new values will be especially important in avoiding multicollinearity when the extended Grunwald-Winstein equation ( extended by addition of a term involving solvent nucleophilicity) is used to correlate solvent-induced changes in the specific rates of solvolyses involving a bromide or iodide ion leaving group.