Conductivity Titration of Gelatin Solutions

The combination of proteins with acids has been studied by Loeb I and others largely by means of hydrogen electrode measurements. The present work constitutes an attempt to apply the method of conductivity titration to the determination of the combining capacity of a protein for acids. The first work which indicated that the measurement of electrical conductivity could be used in volumetric analysis seems to have been done by Kohlrausch * in 1885, and since then the method has been given in standard text-books. 3 Recently the method has been extensively used by Kolthoff, 4 who has outlined the theory on which it depends. In the neutralization of a weak base by a strong acid, the conductivity at first increases because of the formation of a highly ionized salt, and since at first practically all of the added acid is used up to form the salt, the conductivity increases as a linear function of the amount of acid. As more acid is added, the formation of the salt is no longer complete on account of hydrolysis, and the increase in conductivity becomes faster, due to the presence of the highly mobile hydrogen ion. Finally, after enough acid has been added to combine with all the base and to repress the hydrolysis, the conductivity increases much more rapidly on the addition of further acid, since