MOBILITY STUDIES WITH COLLOIDAL SILICIC ACID¹

Abstract

The mutual reactions of colloids attending the mixing of systems of opposite sign have been investigated by electrokinetic methods (1, 2, 3, 7). Of these, the method employing the ultramicroscope offers a distinct advantage, since mobilities of mixed systems can be observed throughout the concentration range including the flocculation zone. Accordingly, it is possible to study the mutual coagulation process as well as the mutual effects produced by varying concentrations of components in stable mixtures. In the latter case information can be obtained relating to the change in stability of the components and, in a restricted sense, to changes in the state of the particles, e.g., whether the components are completely independent, or combined (owing to capillary-active properties), or partially combined and partially free (7).Weiser and Chapman (9) are of the opinion that the mutual coagulation process may be determined by a number of factors: namely, electrical neutralization, mutual adsorption of the particles, interaction between stabilizing ions, and the presence of excess electrolyte in the sols. These same factors probably influence the state of the particles in stable mixed systems. On the other hand, exponents of a chemical mechanism explain mutual coagulation as a result of a reaction between the stabilizing electrolytes. Thus Thomas and Johnson (8) found for the undialyzed system ferric oxide-silicic acid that coagulation was at an optimum where SUMMARY1. An electrokinetic study of colloidal silicic acid has been made with the aid of an ultramicroscope.2. The effect of electrolytes, pH, and of colloids of opposite sign on the mobility has been investigated.

The Behavior of Colloidal Suspensions with Electrolytes.

“…Also in line with this idea are the experiments of Hazel (23) (figure 11) in regard to the behavior of the electrophoretic velocity of bentonite particles with the concentration of sodium hydroxide. The initial reduction in the electrophoretic velocity may be attributed to the replacement of the hydrogen ions, which react with the hydroxide ions to form water, by the sodium ions, which are adsorbed to a lesser extent in the diffuse layer and are more easily ionized from the bentonite particles.…”

Streaming Potential Measurements and the Adhesion of Phosphors on Cathode Ray Screens

“…The zeta potentials were calculated from a knowledge of the streaming potential, cell constant, cell resistance, and pressure difference by the method described previously (1). 4 Cell consfants for diaphragms filled with phosphor and with powdered glass were determined using 0.0100, 0.100, and 1.00N KC1 and with saturated sodium chloride solution. All solutions gave the same cell constant indicating negligible surface conductance.…”

Industrial Adhesives

“…With larger amounts of moisture the more colloidal forms, 3.98-and 3.32-ratios, go through a stage in which they may be formed into a ball and bounced on a hard surface without cracking apart. This surprising elasticity has excited considerable interest but it is not fully explained (9,12). Even at rather low humidities resiliency may be maintained by the incorporation of materials such as sugar, glycerol, rubber latex, or mica.…”

“…At the intersection with the line of solution V = 1.87. Experimental value = 1.89 (12). LITERATURE CITED (1) Barkelew, Valentine, and Hurd, Chem. Eng.…”