An important process in the treatment of water, sewage, and industrial wastes is the formation of suspended floes which can be effectively removed from the liquid by settling or filtration. This process is known as flocculation or coagulation. Prior to 1920, the nature of the process was not well understood by sanitary engineers and was frequently confused with mixing–the purpose of which is to distribute the coagulating chemicals in the liquid being treated so as to promote solution of the chemicals and completion of the chemical reactions. It has since been learned that flocculation is a physical process requiring gentle turbulence and time. Little progress has been made, however, in the scientific development of the principles involved and their application to design.