CRYSTALLIZATION 69 



of thickening, because many substances which were 

 soluble in the thin juice, become insoluble as it thickens. 

 These substances make the juice turbid, and also deposit 

 themselves in the tubes, which, therefore, require con- 

 stant cleansing. In the case of cane juice, phosphate, 

 sulphate, carbonate, silicate and oxalate of lime, oxide 

 of iron, silica and a few organic impurities are found 

 in this deposit. For this turbid, thickened juice, a 

 further clarification is necessary. If it has been through 

 the double carbonatation there will be no difficulty in 

 the filtration, but in the case of cane juice from the ordin- 

 ary defecation it must be treated again in the defecating 

 pans, and neutralized, if necessary, with sulphurous 

 or phosphoric acid, or, if acid, with soda. These help 

 the settlement of the precipitate. Acidity in thickened 

 cane juice may come from fermentation. The only 

 way to avoid this fatal trouble is cleanliness. That 

 must be the first rule in every sugar factory or refinery. 

 The triple-effet is now used universally in all large sugar 

 factories, and has sometimes become a Quadruple-effet. 

 Many modifications have appeared but need not be 

 described here in detail, though they are interesting 

 and instructive. Some are film evaporators, and some 

 substitute horizontal for vertical pans. 



The thick juice, after filtration, goes to the vacuum 

 pan, and its treatment there depends on the kind of 

 sugar to be made. It may be boiled into large grained 

 yellow crystals, as in Demerara ; or into still larger 

 grained sugar which is afterwards washed white, as 

 in France ; or into small grained sugar, afterwards 

 washed white, as is the practice in Germany, Austria, 

 and Russia, in making " granulated " ; or into a supe- 

 rior crystalline raw sugar for the use of sugar refiners, as 

 is the case in Cuba, Peru, St. Domingo, Java, and many 

 other progressive cane sugar countries, and also in most 



5-(i 4 6 3 ) 



