The conductivity of aqueous solutions of lanthanum ferricyanide

The conductivity of lanthanum ferricyanide in water has been measured at 18, 25 and 30° C. In dilute solutions the salt shows the behaviour of a comparatively weak electrolyte, and when the limiting Debye-Huckel and Onsager equations are applied to thirty measurements at ionic strengths lower than 0·002, a constant value K = 1·82 x 10 -4 is found for its dissociation constant at 25° C. The dissociation constants at 18 and 30° C have also been calculated, and hence ∆ H , ∆ G and ∆ S for dissociation. At the higher concentrations the conductivity curve shows abnormalities which find a reasonable explanation in the theory that the degree of dissociation falls to a minimum value of approximately 0.5, and increases again at higher concentrations. The composition of the hydrate stable at room temperature is found to be LaFe(CN) 6 ,5H 2 O. One molecule of water is readily lost over concentrated sulphuric acid, and this may account for the lower degrees of hydration reported in the literature.