Peptization

PEPTIZATION, the dissolution of a colloidal precipitate by means of electrolytes that impart an electric charge to the colloidal particles, necessary for maintaining their stability. This is achieved by adding an electrolyte, one of the ions of which is more strongly adsorbed and imparts to the particles of the colloidal precipitate a sufficient electric potential to cause reverse dissolution. It is necessary only that the particles that have fallen out of solution have not lost their individuality, that the connection between them remains sufficiently loose. Only such a connection usually occurs in coagulation. In the larger aggregates that form, the constituent ultramicroscopic particles are separated from each other over almost their entire surface by thin layers of water. Only in the subsequent compaction and drying of the precipitate does a closer and often inseparable connection occur between the primary particles and the secondary ones. Therefore, as a general rule, any freshly formed coagulum can be redispersed by the action of electrolytes. Like other processes depending on the action of ions on the charge and stability of hydrophobic colloids, peptization requires in most cases an extremely small amount of electrolytes, often completely negligible compared to the amount of precipitate that they convert into solution. Peptization is one of the most important and widely used methods for preparing colloidal solutions. The precipitate from which a sol is to be prepared must consist of sufficiently fine particles. It is first thoroughly washed from foreign impurities and then a suitable peptizing agent is added. An example can be the peptization of iron hydroxide by its own soluble salt: |Fe(OH)₃j+FeCl3 = [Fe(OH)7|Fe"-+3Cl''. Peptizing agents (usually acids or alkalis) that form ions retained on the surface of the peptized substance through chemical interaction with it act even better.

PEPTIC ULCER

236 peptizing agent.