$word_{count}$: 210

Tyndall effect: light scattering by particles (1-1000 nm range). Blue sky = Tyndall scattering by atmospheric particles. Brownian motion: random zig-zag movement due to unequal molecular bombardment. Stabilises colloid by preventing settling. Electrophoresis: migration of charged particles to oppositely charged electrode. Cataphoresis (particles to cathode = positive colloid). Anaphoresis (to anode = negative colloid). Electroosmosis: movement of dispersion medium under electric field. Coagulation: neutralisation of charge by electrolyte. Hardy-Schulze: coagulating power proportional to valence of oppositely charged ion. Negative colloids (As2S3, Au, Ag, starch, clay): coagulated by cations: $Al^{3+}$ > $Mg^{2+}$ > Na+. Positive colloids (Fe(OH)3, Al(OH)3): coagulated by anions: $PO4^{3-}$ > $SO4^{2-}$ > Cl-. Gold number: mg of protective colloid (lyophilic) needed to prevent coagulation of 10 mL gold sol by 1 mL of 10% NaCl. Lower gold number = better protective action. Gelatin (0.005-0.01) > albumin > starch > gum arabic.