# Colloids dispersion classification

I've been teaching chemistry for 25 years, but now I'm confused. Is a colloidal dispersion a heterogeneous or homogeneous mixture? I've seen both answers on the web.

• +1 for the "teaching chemistry for 25 years and am still learning it" - one of the best things about chemistry – Sean Doris Feb 26 '16 at 6:32

A colloid is a homogeneous substance, consisting of large molecules or ultramicroscopic particles of one substance dispersed through a second substance. Colloids are classified as homogenous mixtures because the particles (generally of sizes $1-1000\:\mathrm{nm}$) do not settle out and cannot be separated out by ordinary filtering or centrifuging like those in a suspension, though the particle sizes are still greater than those in a true solution.