If the particles in a solvent are so large that they settle out unless the mixture is constantly stirred or agitated, the mixture is called a suspension.
Colloids are mixtures that contain particles that are intermediate in size between those found in solutions and suspensions. These particles are dispersed throughout the mixture and do not settle out over time, making colloids appear homogeneous.
When a beam of light rays is passed through a colloid, particles of the dispersed phase scatter the light rays and the path of the light becomes visible. The scattering of light by the colloid particles is known as the Tyndall effect.
