"some investigations on the electrification of interfaces"

Abstract

Using a method developed by C. Curry at Durham University, in which the charge on a drop falling under gravity can be measured by the deflection from there vertical in a transverse electric field, experiments were performed to measure the neutral charges acquired by water drops in the air. Those proving unsuccessful, attempts were made to increase the consitivity of the method by measuring the deflection in an electric field after the drops have fallen into benzene. It was found, however, that these drops acquired a characteristic negative charge, he charge being due to impurities in solution in the water, and being proportional to field intensity and drop radius. In order to gain more information on the benzene water interface, experiments were performed using benzene drops in aqueous solutions. These drops had a negative charge in distilled water and the drop charge increased to a maximum or “saturation” charge in alkaline solutions. The reasons for attributing the negative charge to chemical adsorption of hydroxyl ions are given together with a mathematical explanation of the charge – hydroxyl ion concentration curves obtained. Yukherjce’s equation for neutralization of charge on colloidal particles was checked by results obtained using benzene drops in Lanthanum Nitrate solutions. Other non conducting drops were found to behave in a similar manner to the benzene drops, and using carbon tetrachloride spheres the charge was found to be proportional to the cube of the radius, over most of the range covered (0.2 – 1.8m.m. diameter). The charge was also seen to be connected with conditions of turbulence in the liquid round the drops. Some experiments with pure mercury drops were made and a change in sign of the drop charge from positive to negative was observed in sufficiently large potential gradients, in alkaline and neutral solutions. A possible explanation of this reversal phenomenon is given, and results obtained with neutral salt solutions tend to to verify the simple theory.