Colloid

Colloid, mixture in which particles of one substance are dispersed in another. Colloids are similar to solutions and suspensions. What determines the difference is the size of the particles of the substance that is distributed. In a solution, the particles are molecules. In a suspension, they are much larger, visible either with the naked eye or a microscope. A colloid has particles larger than molecules but too small to be seen with a normal microscope. Colloids can be categorized according to whether the substances mixed together are solids, liquids, or gases. For instance, a gas may be dispersed in a liquid to form foam. A liquid dispersed in another liquid forms an emulsion. A liquid dispersed in a solid is a gel.