The Nature of Adsorption in the Precipitation of Arsenic Trisulfide by Acids

A study of the flocculation of colloid sols is of great importance, both from the practical standpoint - to determine the proper conditions for stabilizing prepared sols or in the flocculation of undesirable sols, and from the theoretical standpoint - to determine the actual structure of colloids. Much experimental work has been done on the flocculation of various sols by electrolytes, and several general rules have been evolved, as the Schulze-Hardy rule and the Freundlich adsorption isotherm. As a result it has been postulated that an important factor (if not the determining factor) in coagulation by electrolytes is the adsorption of the electrolyte by the micellae of the sol. However, very little work has been done with the determination of the adsorption found in the flocculation of sols by acids, or with the comparison of the adsorption of various acids in this coagulation. In general, such adsorption has been shown to be anomalous in comparison with other electrolytes. Therefore, it is the opinion of the writer that an investigation of acid adsorption in the flocculation of colloid sols is of considerable value in determining the theory of the mechanism of flocculation. The sol chosen for the experimental work is colloidal arsenous sulfide, since it is easy to prepare in reasonable high concentrations, fairly stable, and flocculable by acids. A glass electrode pH measuring device is chosen to measure adsorption since such a device is of high accuracy yet does not require either mechanical or chemical disturbance of the sol