ABSTRACT
Our lives are a continuous encounter with solid particles of different sizes, ranging from stones on a beach, sand particles, or dust floating around in the air, without our being especially aware that there exists a special relation between particle size (surface area) and their characteristics. The rather small particles in the range of size from 50 Å to 50 μm are called colloids. The most obvious difference is apparent between sand particles and dust particles. It is fascinating to observe how dust or other fine particles remain in suspension in the air. In the 19th century, it was observed under the microscope (Brown) that small microscopic particle suspended in water made some erratic movements (as if hit by some other neighboring molecules). Since then this has been called Brownian motion. This erratic motion arises from the kinetic movement of the surrounding water molecules. Thus, colloidal particles would remain suspended in solution through Brownian motion only if the gravity forces did not drag these to the bottom (or top).
