RAW SUGAR 



433 



The last two classes of colouring matter are objectionable to the refiner as 

 resistant to the action of bonechar. All these characteristics are of more 

 interest to the refiner than to the producer. The former is benefited by 

 the absence of insoluble matter, by a large and regular grain with the absence 

 of nests of crystals cemented together by molasses, by a nucleus formed 

 from syrup and not from seed grain, and by little colour, especially that 

 formed by overheating or by the breaking down of reducing sugars. 



Sugar Drying. In the manufacture of white sugar the crystals are dried 

 after they are discharged from the machine. The apparatus usually employed 

 for this purpose consists of a long inclined drum, Fig. 272, which is caused 

 to rotate about its axis at a speed of about 12 revolutions per minute. At- 

 tached to the inner periphery of the drum are a series of paddles, which serve 

 both to carry the sugar forward and at the same time to throw it down in 

 a shower as each paddle in turn reaches the upper point in its revolution. 

 A current of hot air is drawn through the drum in a direction counter to 

 the travel of the sugar. The air enters at about 180 F. and leaves at about 



FIG. 272 



130 F., while the sugar remains in the drum about twenty minutes. The 

 heating surface consists of an external system of steam-heated pipes, an 

 allowance of 75 sq. ft. per ton-sugar-hour being usually found. These 

 dryers are often made in pairs, the second one dispensing with hot air but 

 being provided with an interior steam-heated drum. Sometimes the drum 

 and hot-air system are combined in one unit, but in this combination there 

 is a tendency for wet sugar to cake on the drum. Quite irrationally this 

 apparatus is frequently called a granulator. 



In some houses it is not unusual to use simpler means for removing some 

 part of the water. These means may take the place of one or more tables 

 caused to rotate rapidly in a horizontal plane. These are arranged in the bin 

 in which the sugar is discharged, and by the exposure of a large area permit 

 of the removal of some of the water. In Java it was, and perhaps still is, the 

 custom to dry the sugar by exposure on the flat roofs of the factories. 



Drying of sugars, though of great benefit to the producer of raw sugar, 

 is but little practised. The advantages to the latter are discussed in 

 detail in a following section. To these benefits must be added the protection 

 afforded against deterioration, since it has been conclusively shown that a 

 concentrated film of molasses forms a medium in which the activity of micro- 

 organisms is suspended. 



2G 



