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CHAPTER XVI 



Prior to this time both beet and cane 



great influence on sugar manufacture, 

 sugar houses speciahzing in white sugars had employed animal charcoal 

 filtration, and the first efforts to eliminate this agent may be traced to Melsens' 

 work. In Louisiana the application of sulphitation dates from i860, where 

 it was used under Stewart's patent (U.S. 22590, 1859), and at about the same 

 time it was introduced into Mauritius through the agency of leery. 



Sulphitation Processes. — There are a great many ways in which sulphur 

 is used alone and in combination with other agents. Some of these methods 

 are described below. 



Raw Juice Sulphitation. — In the older schemes, sulphitation was carried 



out on the raw juice, the lime and sulphurous acid being added separate^ 



to the cold juice, practice diftering as to which defecant was added first. 



In either case the same end point was aimed at, namely, a juice with an acidity 



in terms of phenolphthalein of from 0-5 to 0-7 c.c. normal per 100 c.c. 



When the operation is conducted on cold juice, however, a 



rather serious trouble arises. Calcium sulphite is more soluble 



at ordinary than at higher temperatures, and it has also the 



property of forming supersaturated solutions. Consequently, 



when a cold limed and sulphured juice is heated, it deposits 



large quantities of calcium sulphite on the tubes of the heaters, 



and also upon the tubes of the evaporator. Java practice has 



developed a routine which satisfactorily eliminates this trouble. 



The raw juice is heated to a temperature variously quoted as 



70° C. to 80° C, over which region the solubility of calcium 



sulphite is at a minimum. After reception of the hot juice in 



open vessels, the necessar}^ quantities of milk-of-lime and of 



sulphur dioxide are added simultaneously. The treated juice 



now passes through a second heater, where its temperature is 



, raised to 100° C, and thence to the settling or filter supply 



/4 Ly~t^ tanks. In this way is avoided the coloration due to lime- 



FiG. 170 reducing sugar decomposition products following on heating 



after addition of lime only, or inversion due to heating after 



addition of sulphur dioxide only. 



Any deposit of scale which may form on the second heating can be sys- 

 tematically removed by alternating the flow of juice through the first and 

 second heaters. Whatever method is adopted, it seems general to use about 

 twice as much lime as would be used in ordinary lime defecation, so as to 

 obtain a sufficient bulk of calcium sulphite to carry down and entangle the 

 colloids ; at the same time the simultaneous application of lime and sulphur 

 dioxide reduces the quantities that are requisite for a good defecation. 



The action of sulphur dioxide on cane juice has been examined by 

 Browne.^ He shows that due to the action of sulphur alone a precipitate 

 amounting to 0-3 to 0-4 per cent, on the weight of the juice is formed, and 

 the composition of this precipitate he finds as below : — 



