64 



general lieating purposes throughout the factory. The water of con- 

 densation secured from this steam after it is used for the purposes 

 named is pumped back to the boiler feed tanks and again used for 

 boiler supply. One of the difficulties in the repeated use of this water 

 after passing through the mill engines is that it contains oil and other 

 impurities which become mixed with it on passing through the engines, 

 pipe lines, and steam belts where it is used. Where water is scarce that 

 evaporated from the juice in the multiple effects and vacuum pans can 

 also be used for boiler supply, but often contains impurities which make 

 it undesirable, 



Crystallizers. — After the massecuite has been discharged from the 

 \'acuum pan it may be handled in a number of ways, but most of the 

 modern mills place it in closed crystallizers equipped with a stirring 

 device for keeping it in motion during the period of a few hours or 

 even for several days where the sugar being manufactured is of low 

 grade. This stirring aids in the building up of the sugar crystals by 

 any additional crystallizable sugar which may remain in the massecuite 

 and keeps the material in a semifluid state so that it will flow into the 

 centrifugals for purification. 



Where closed crystallizers are not used the massecuite is often placed 

 in open mixers which may or may not be provided with stirring devices 

 similar to crystallizers. In the smaller mills this mixer is generally 

 placed just above the centrifugals and so arranged that the contents 

 may be emptied directly into the crystallizer baskets. Some of the 

 older mills, especially of the smaller capacities, have neither of these 

 but use a small tank car or truck sometimes called "coolers." Enougrh 

 of these should be provided to store the entire contents of the vacuum 

 pans in use and have a surplus to avoid congestion in case any accident 

 happens to the centrifugals. 



Centrifugals. — Sugar centrifugals are an essential part of modern 

 milling equipment. These machines are made singly or in batteries of 

 from two to eight arranged in continuous iron frames with the neces- 

 sary supports and connections for their operation. The simplest form 

 is driven by a belt to each machine, though there is a tendency to drive 

 them by water or by electric motors. The essential working part of a 

 centrifugal is an iron basket 76 to 102 centimetei-s in diameter suspended 

 on a vertical shaft at the top of which the driving arrangement is at- 

 tached. There is a large opening in the bottom of the basket which is 

 closed during operation by a conical steel cover fitting around the shaft. 

 There; is also a receiving trough in the bed of the machine just under 

 the basket into which the molasses thrown out of the sugar catches 

 and flows away to the molasses tank. The operation of these centrifugals 

 is quite simple and consist in placing 100 lo 200 kilos of massecuite 

 in the basket after which it is set in motion and the centrifugal force 



