Final Crystallization.—The sirup is now ready for the final process, which takes place in what is known as the vacuum strike pan, Fig. 74. A considerable quantity of sirup is introduced so as to cover the lower coils of this pan and, after the vacuum is established by a pump, evaporated to the crystallizing point. An additional quantity of cold sirup is then drawn into the pan, chilling the mass and thus producing incipient crystallization in the form of extremely minute crystals. The evaporation is now continued with the addition of sirup from time to time, by which process the sugar crystals begin to grow. In the course of a few hours the pan is full of crystals of the size desired.
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Fig. 74.—Vacuum Strike Pan.—(Farmers' Bulletin 52.)
Purification of the Sugar.—The vacuum is broken and the crystallized mass of sugar drawn into a mixing apparatus whereby all lumps are broken up and a uniform magma secured. This is done while the mass is still warm. Were it allowed to cool it would be extremely difficult to break it up. The warm mixture is then passed into the centrifugal machine, by means of which the molasses is separated from the crystals and these remain as white pure crystals in the pan. The whole process of separating the juice from the massecuite, as the mass is called, occupies only a few minutes. Thus the sugar is often centrifugalled and in the barrels before it is cold from the vacuum pan.
