CANE SUGAR. 



than can saturated steam ; the very reasons that make superheated steam 

 advantageous 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 pots 

 over a naked fire, a system still pursued by the ryots of India and on a fairly 

 large scale in Barbados, the whole system of tayches being called a copper wall. 

 The earliest improvement over this method was the introduction of steam-heated 

 pans, followed by the Aspinall, Wetzel, and other devices ; all these consisted 

 essentially of an open pan in which revolved steam-heated coils or discs, so 

 arranged that half the coil was immersed ; the rotating coil carried upwards a 

 thin film of liquid and thus exposed a large surface to evaporation. 



In 1865, Fryer introduced the Concretor, a patent which has been 

 extensively used. In this plant the thin juice flows over a series of trays 

 placed over a flue, the whole being built on a slight incline ; the flue is about 



FIG. 157. 



forty 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 revolving 

 cylindrical vessel, in the interior of which are fitted scroll-shaped plates, so 

 that, as the cylinder revolves, a large surface is exposed to evaporation ; at the 

 same 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 in 

 the manufacture of * basket ' sugar in the Straits ; the final concentration is 

 effected by a revolving coil containing heated oil, the temperature of which 

 can be regulated. 



286 



