James W. McBain

The osmotic activity and conductivity of aqueous solutions of some typical colloidal electrolytes

Abstract 1. 1. The osmotic coefficients of aqueous solutions of 10 different anionic and cationic colloidal electrolytes have been measured by freezing point depression, now bringing the total number of those investigated to 64. Conductivities were also measured for these and two other materials too insoluble at 0°C. for freezing point determinations. 2. 2. The relative lowering of conductivity with increasing concentration is less than that of osmotic coefficient. In the case of polycyclic structures, such as a bile salt or sodium abietate, the latter measurement shows the presence of colloid with a critical concentration, whereas this does not appear in the conductivity curve. 3. 3. Addition of dimethyl phthalate, a substance insoluble in oil and water but solubilized by soap solutions, appears slightly to decrease colloid formation as reflected in osmotic coefficient and equivalent conductivity. 4. 4. The colloidal behavior of the laurate of several complex organic bases has been compared with that of potassium laurate. 5. 5. An ordinary molecule, sucrose, lowers the freezing point of water to the same extent as it lowers the freezing point of a solution of the colloidal electrolyte, potassium laurate.

Conductivity at the interface between pyrex glass and solutions of potassium chloride

Abstract 1. 1. Surface conductances at the interface of fritted Pyrex glass-0.0005 N potassium chloride have been observed with precision of 1%. 2. 2. This surface conductance is independent of frequency and intensity of the measuring current, but varies greatly with time over periods of months and with cleaning of the surface. 3. 3. Hydrodynamic resistance to flow through the fritted glass may increase with time by an order of magnitude, while its resistance to movement of ions remains constant to within 0.1%. 4. 4. This hydrodynamic resistance is not due to occlusion of air bubbles nor to electrokinetic effects.

Changes in solubilizing power with concentration for various detergents

Abstract 1. 1. The solubilization of dyes by a series of very different detergents has been studied over a range of concentration for each detergent. 2. 2. The change in solubilizing power with change in concentration is very different for different detergents. Some show a pronounced maximum at a concentration at which they have just become colloidal. Some show maxima and minima, or other changes with concentration. 3. 3. It follows, in agreement with other evidence, that the micelles or colloidal particles in any one concentration of a detergent differ from those in other concentrations of the same detergent. There must be an equilibrium between different kinds of micelles present in the same solution, changing with concentration and other factors.