THE COMBINATION OF SALTS AND PROTEINS. II . A METHOD FOR Tm~ DET~.RMINATION OF THE CONCENTRATION OF COMBINED IONS FROr~ MEMBRANE POTENTIAL MEASU'REMBNTS. BY

The exact determination of the combination of proteins with the ions of electrolytes has been limited practically to those cases in which concentration cells can be used. Bugarszky and Liebermann 1 found by this method that the hydrogen ion is very largely combined and chloride to a much less extent. These measurements have been repeated and confirmed by a number of workers, and extended by Pauli and Matula ~ to Ag +, which was found to be also quite largely combined. Pauli and Samec s also found that the solubility of slightly soluble salts was increased by proteins, and tMs furnishes an additional method for determining the amount of combined ions. Both methods, however, are limited to a very small number of ions and only in rare cases, such as HC1 or ZnC12, is it possible to determine the combination of both ions. I t was pointed out in the preceding paper ~ that the Donnan equilibrium furnishes a general method which can be used for any ion, provided the distribution of one ion and the analytical composition of the solutions be known. I t was shown that using gelatin particles and determining the theoretical ion ratio from C1electrode potentials, the concentration of Zn ions combined with the gelatin could be calculated, and agreed quite well with the values determined directly by concentration cell measurements. This method is also limited since it can only be used with gelatin and under certain conditions, since in alkaline solutions the chloride electrodes