All measurements were made at 25 * 0.01°.Materials, Apparatus and Method.-Chemically pure barium bromide was twice recrystallized from distilled water and finally from conductivity water. A stock solution was made from this and the barium bromide content determined gravimetrically by the silver bromide method. Weighed portions of this solution were diluted to the approximate concentrations, boiled to remove oxygen and finally diluted with oxygen-free water to the desired molality. The dilutions were made with an accuracy of about 0.1%.The mercury and amalgams were prepared in the manner previously described.1
A simple and reliable procedure has been described whereby the quinhydrone electrode may be used in cells without liquid junction, employing vacuum technique.2. The reproducibility of the quinhydrone electrode in 0.01 M hydrochloric acid solution has been carefully studied, employing the cell Pt/ quinhydrone, HC1 (0.01 M)/AgCl/Ag. The electromotive force of this cell has been found to be reproducible to within a tenth of a millivolt from 0 to 40°, although side reactions destroy the equilibrium after a short time at temperatures above 30°.3. Values have been obtained from 0 to 40°for the potential of the above cell and the normal potentials of that cell and the cell, Pt/quinhydrone, HC1/H2, with an accuracy of ± 0.1 mv. from 0 to 25°and ± 0.15 mv. from 30 to 40°.
THE electrometric methods that have been developed for determining lead are not of practical value. Several adaptations have been made of the thermionic electron tube to this and other titrations (1, 3, 4). The devices discussed in this article were designed to increase the speed and accuracy with which potentiometric titrations might be made. An ideal potentiometric titration apparatus should indicate the equivalence point-i. e., where AE/ A V becomes a maximum-without the necessity of constructing a curve.
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