The Tyndall Effect is the effect of light scattering in colloidal dispersion, while showing no light in a true solution. This effect is used to determine whether a mixture is a true solution or a colloid.
"To be classified colloidal, a material must have one or more of its dimensions (length, width, or thickness) in the approximate range of 1-1000 nm." Because a colloidal solution or substance (like fog) is made up of scattered particles (like dust and water in air), light cannot travel straight through. Rather, it collides with these micro-particles and scatters causing the effect of a visible light beam. This effect was observed and described by John Tyndall as the Tyndall Effect.
The Tyndall effect is an easy way of determining whether a mixture is colloidal or not. When light is shined through a true solution, the light passes cleanly through the solution, however when light is passed through a colloidal solution, the substance in the dispersed phases scatters the light in all directions, making it readily seen.
For example, light being shined through water and milk. The light is not reflected when passing through the water because it is not a colloid. It is however reflected in all directions when it passes through the milk, which is colloidal. A second example is shining a flashlight into fog or smog; the beam of light can be easily seen because the fog is a colloid.
- Heidorn, Keith PhD. The Weather Doctor's Weather Almanac: John Tyndall. NASA 2006
- John Tyndall (1896). The Glaciers of the Alps. Longmans, Green and Co.. Republished as Tyndall, J. 1860 (2005). The Glaciers of the Alps. Adamant Media Corp.
- Petrucci, Ralph, William Harwood, F. Herring, and Jeffry Madura. General Chemistry: Principles and Modern Applications 9th Ed. New Jersey, 2007.