In the thin coherent hemin collodion film membranes prepared by a modified method, Cl- ion in the film could be exchanged by No2-, CIO3-, CIO4-, and BrO3- ions by keeping it in contact with neutral aqueous solutions of the respective salts for a prolonged period, the conditioning time varied with the nature of the ions. The film membranes of different salts of hematin prepared could be used in the determination of anion activities of the neutral aqueous solutions of different electrolytes from

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... he measurement of mem­brane potential. In the case of KNO2 the valid range of concentration for the application of Nernst equa­tion was 0-0002 to 0.08 M with molarity ratio 2, and the same for KCIO3, KCIO4 and KBrO3 were (1) 0.0008 to 0.0512 M, (2) 0.0002 to 0.0512 M and (3) 0.0016 to 0.0512 M respectively, the experimental error in the measurement being ±3.5%.