3 A metal in equilibrium with tow slightly soluble salts with a common anion (Class Electrodes) Ag Ag2 S, CdS Ag+, Cd2+S 92S(5)-2Ag*+s (6r-9) CdS Cd2++S2 6r-103) A metal in equilibrium with tow slightly soluble salts with a common Anion (Class Ⅲelectrodes) AgAg2S,CdSAg+ ,Cd2+,S2- , Ag2S(s) 2Ag++S2- CdS(s) Cd2++S2- (6r-9) (6r-10)