426 



CHAPTER XX 



In this scheme the molasses are expelled in the first set of machines, the sugar 

 being dropped without any washing. It is then made up to a magma with 

 purging syrup and redried or affined in a second set of machines. In the 

 first operation the sugar from the first drying is made up to a magma with 

 water, and the resulting " molasses " forms the purging syrup used in 

 subsequent operations, circulating continuously ; the excess as it accumu- 

 lates is boiled into first product, or it may be returned to thin juice, since, 

 being of very high density, it is not advisable to introduce it direct to the 

 pan without dilution. The second quality white sugar may be treated in a 



FIG. 270 



similar way, or after mixing with first molasses it may be dried along with 

 the first massecuite, the factory then producing only one grade of white 

 sugar. The great advantage of double curing lies in the complete classifica- 

 tion of the molasses which it affords. 



When calculating the number of centrifugals required fcr white sugar 

 manufacture, only half the capacity of that accepted for 96 test should be 

 taken, so as to allow for the extra time consumed in washing with water 

 and steam. If steam washing is dispensed with in favour of a sugar dryer, 

 this extra allowance may be decreased. If double curing be installed, 



FIG. 271 



either set should have the same capacity as would be employed with 96 

 test sugar. 



Conveyance of Sugar. Occasionally the dried sugar is discharged direct 

 from the machines into bags, but it is usually conveyed to an upper floor 

 or bagging bin by means of an elevator of the type shown in Fig. 269. The 

 crystals are carried from the machines to this elevator by a screw conveyor, 

 as indicated in Fig. 270, or by a " grasshopper " conveyor, Fig. 271. This 

 consists of a suspended trough, which is supported on flexible inclined blades, 

 and to which a to-and-fro motion is transmitted by means of an eccentric. 



