In order to study the effects of added chlorides on the solubility of cadmium metal in the molten cadmium chloride, its solubility in CdC1 2-KCl-AICl 3 mixtures was determined by measuring the EMF of C / Cd, CdC1 2-KCI-AlC1/ / CdC1 2-KCI-AlC13, Cd(sat.) / C cells. For the Cd-CdC1 2 s ystem, solubility limits were determined as 0.156 (molar fraction) at 600°C and 0.189 at 7 40°<:;:. It was found that these values increased with the addition of A1Cl 3-rich chloride mixtures, but decreased with the addition of KCl-rich mixtures. Assuming that Cd dissolves into molten CdC1 2 as Cd 2 2+ up to the solubility limit, these effects may be interpreted as an acid-base reaction between the added chloride and Cd 2 Cl 2 in CdC1 2 • A basic chloride such as KC 1 which acts as a Cl-donor stabilizes Cd 2 + ions, and an acidic chloride such as AlC1 3 (Cl-acceptor) decreases the stability of Cd 2+ ions. Based on results in which the contribution of the dilution effect of added salts was eliminated, an ~cidity scale that could quantitatively represent the stren. gth of acidity of chlorides was introduced.