coagulation [key], the collecting into a mass of minute particles of a solid dispersed throughout a liquid (a sol), usually followed by the precipitation or separation of the solid mass from the liquid. The casein in milk is coagulated (curdled) by the addition of acetic acid or citric acid. The albumin in egg white is coagulated by heating. The clotting of blood is another example of coagulation. Coagulation usually involves a chemical reaction. Lyophobic particles (see colloid) lose their electric charge by reacting with oppositely charged particles. Lyophilic particles undergo a reaction that causes them to lose their solubility. In either case coagulation occurs. The formation of a gel by evaporation or cooling of a sol is usually called gelation rather than coagulation.
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