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CANE SUGAR.than can saturated steam; the very reasons that make superheated steamadvantageous for use in engines prevent its satisfactory use for evaporation,where a rapid condensation and quick transference of heat is required.Early Methods.—The earliest method of evaporation was in potsover a naked fire, a system still pursued by the ryots of India and on a fairlylarge scale in Barbados, the whole system of tayches being called a copper wall.The earliest improvement over this method was the introduction of steam-heatedpans, followed by the Aspinall, Wetzel, and other devices; all these consistedessentially of an open pan in which revolved steam-heated coils or discs, soarranged that half the coil was immersed; the rotating coil carried upwards athin film of liquid and thus exposed a large surface to evaporation.In 1865, Fryer introduced the Concretor, a patent which has beenextensively used. In this plant the thin juice flows over a series of traysplaced over a flue, the whole being built on a slight incline ; the flue is aboutforty feet long and the juice travels in a zigzag path about two hundred feet ;reaching the end at a density of about 50° Brix, it flows into a revolvingcylindrical vessel, in the interior of which are fitted scroll-shaped plates, sothat, as the cylinder revolves, a large surface is exposed to evaporation ; at thesame time a current of hot air is blown through. After twenty minutes'treatment in this cylinder the evaporated juice sets on cooling to a solid mass,and is shipped to refineries for further treatment.A modernized form of this scheme is used in Miller's patent employed inthe manufacture of 'basket' sugar in the Straits ; the final concentration iseffected by a revolving coil containing heated oil, the temperature of whichcan be regulated.286