340 CHAPTER XVIII 



earlier in this chapter. The capacities of apparatus with other numbers 

 of effects in series may be obtained from comparison with the quadruple 

 figures recorded here. Probably double and triple effects will have rather 

 larger capacities than calculated, the reverse holding with quintuple and 

 sextuple apparatus. 



The figures quoted here are rather of the nature of maxima, and the writer 

 does not wish to be taken as advising these as a basis of design. 



Development of the Practice of Evaporation. — The earliest method used 

 was doubtless evaporation in vessels over a direct fire. This method sur- 

 vived on the large scale till well into the nineteenth century in the copper 

 wall so well described by Ligon, Dutrone and other early writers. It is 

 still to be found in parts of the Southern States, and South America; and in 

 British India very large quantities of sugar are thus produced at the present 

 time. The final stage of the direct fire-heated system is to be found in 

 Fryer's concretor (patents 418 of 1865 and 2144 of 1868), which was once 

 in very extended use. In this system the juice travelled in a thin stream 

 in a zigzag course over a heated surface. It was finally concentrated almost 

 to dryness in a rotating cylinder, in which were revolving scrolls. The 

 resulting material was shipped under the name of concrete sugar without 

 separation of the molasses. 



Steam as the heating agent first appears in Wood's patent (1492, 1785), 

 which employs a double-bottomed apparatus. This was followed by the 

 introduction of a tubular heating surface in Taylor's patents (4032, 4197, 

 1816), which, in the eliminator or skimming pan, survives almost unchanged. 

 The substitution of the coil for the tubular heating surface was due to 

 French engineers. An attempt to improve on steam is seen in Wilson's 

 patent (4095, 1817), which proposes the circulation of heated oil. A variant 

 of oil is the use of concentrated salt solutions as found in Ure's patent 

 (6165, 1831). Heated oil is still used in the manufacture of basket sugar 

 in the Orient under Miller's patent (22438 of 1899). 



Increased rapidity of evaporation with increased surface is recognised 

 in Wyatt's patent (4130, 1817) ; he caused spheres or discs to rotate partly 

 immersed in the liquid. This idea was developed further by Cleland (patent 

 5520, 1827) and Aitchison (5848, 1829). who made the rotating elements 

 hollow and admitted steam to their interior. This type of evaporator 

 was further developed by Bour (patent 523 of 1854), who employed opposed 

 hollow spherical caps united along their bases and carried on a horizontal 

 rotating shaft. Another form took the shape of a helix with very flat angle, 

 rotating about a horizontal axis. The form most used is that indicated in 

 Fig. 187, and known as a Wetzel. It is contained in patent 3031 of 1867 

 issued to Bourron, though in use before this date. Many years later these 

 devices have been proposed for use in the vacuimi pan, as in McNeil's patent 

 (8814 of 1899), which foUows Bour's model, and in Czapiowski's patent 

 (15031 of 1902), which resembles the Wetzel pattern. All the above devices 

 for film evaporation employed moving heating surfaces ; a stationary heat 

 surface, over which the juice flows in a film, is first found in Dihl's patent 

 (3965, 1815), and is quite efficiently developed in Cleland's (4696, 1822). 

 Since then film evaporation with fixed heating surfaces has formed a frequent 

 subject of invention, as recently found in the patents of Yaryan (14162 of 

 1886) ; of LiUie (3006 and 12391 of 1888, 11686 of 1890) ; of Meyer and 

 Arbuckle (4218, 9078 and 19962 of 1903) ; and of Kestner (24024 of 1899). 



