In most general chemistry and introductory physical chemistry classes, critical point is defined as that temperature-pressure point on a phase diagram where the liquid-gas interface disappears, a phenomenon that generally occurs at relatively high temperatures or high pressures. Two examples are: water, with a critical point at 647 K (critical temperature: T[subscript c]) and 215 bar (critical pressure: P[subscript c]); and carbon dioxide, with a critical point of 304 K (T [subscript c]) and 73 bar (P[subscript c]). In colloid chemistry, there is another critical point, which occurs at a specific temperature and mole fraction in a specific binary liquid system where immiscible or partially miscible species become completely miscible. These phenomena of colloidal systems occur at atmospheric pressure and over a temperature range which, for some systems, includes room temperature ([similar to]300 K). The purpose of this demonstration is to show this critical-temperature phase-transition phenomenon for a specific binary liquid system, where T[subscript c] is approximately 300 K. (Contains 2 figures.)