Process by which there is a net flow of matter from a region of high concentration to one of low concentration. It occurs fastest in liquids and slowest in solids. Diffusion can be observed by adding a few drops of food colouring to a glass of water. The scent from an open bottle of perfume quickly permeates a room because of random motion of the vapour molecules. A spoonful of salt placed in a bowl of water will eventually spread throughout the water.

This entry comes from Encyclopædia Britannica Concise.
For the full entry on diffusion, visit Britannica.com.

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