264 The Sugar-Beet in America 



reason, evaporation is carried on under reduced pres- 

 sure which lowers the boiling point of the liquid. After 

 the juice is reduced from about 82 per cent of water to 

 about 40 per cent, it is again treated with sulfur and 

 filtered in a manner similar to that used for the "thin 

 juice." This is the final process of purifying the beet 

 juice, which is then ready for graining. 



In refining cane-sugar, there is no treatment with sulfur ; 

 impurities are removed with bone black. This is the 

 chief difference in the method of making sugar from cane 

 and from beets in the United States. In Europe, where 

 raw beet-sugar is produced by many factories, this prod- 

 uct also is refined by the aid of bone black. In early 

 days blood was used extensively in sugar refining, but this 

 practice has now been discontinued entirely. 



GRAINING 



The vacuum-pan serves not only for evaporating the 

 sirup but also for crystallizing the sugar. This pan is a 

 large cast-iron tank in which the air pressure can be kept 

 low to reduce the danger of browning the sugar by high 

 heat. If the juice has been purified properly, there is no 

 trouble about producing good sugar in this pan; but if 

 impurities remain, it is difficult to obtain good crystal- 

 lization. This mixture of crystals and sirup is called 

 " massecuite." It is run through a centrifugal machine, 

 like that shown in Plate XXIX, revolving at a rate of 1200 

 revolutions a minute. The sirup is thrown out through 

 fine perforations in the wall of the machine, and the 

 crystals of sugar remain, dropping out through the bottom 



