Diffusion
a word having several applications. (1) The act of diffusing or spreading about of a liquid, fluid, etc.; (2) a spreading or diffusing abroad of a matter; (3) the state of being spread or dispersed widely; (4) the act of spreading, extending or propagating widely, as the diffusion of knowledge; (5) copiousness, exuberance of style, prolixity, verbosity. Diffusion of gases is the passing of one gas into the space occupied by another. The name given to that phenomenon by which the composition of the atmosphere is kept uniform, or nearly so. Gases diffuse into one another according to a fixed law, that is, inversely as the square root of their densities.
Diffusion of heat is a term applied to those modes by which the equilibrium of heat is effected-viz., conduction, radiation, and convention. Diffusion of liquids: When two liquids that are capable of mixing are put in contact they gradually diffuse one into the other, notwithstanding the action of gravity.