'Sensitizing' by Protective Colloids

THIS is the name given1 to the following phenomenon. It was observed2 that the addition of a quite small amount of a hydrophile colloid to a sol of a hydrophobe colloid caused the latter to be coagulated (precipitated) by a much smaller amount (at much lower concentration) of a precipitating electrolyte than in total absence of the protective colloid. However, suitable larger amounts of the latter made necessary larger amounts of precipitating electrolyte than in the absence of the hydrophile colloid, hence the term 'protective colloid' for the latter.