CONSTITUENTS OF PLANTS 369 



solution, in a series of vessels. The water comes in contact first 

 with beet slices nearly exhausted of sugar, then it is brought in 

 contact with slices richer in sugar, and finally passes through the 

 vessel containing fresh beet slices. This system exhausts the 

 beet, and at the same time secures a comparatively strong solu- 

 tion of sugar. 



The sugar juice is acid. It is treated with lime to neutralize 

 the acid, which would otherwise invert the cane sugar when the 

 juice is heated and decrease the yield. The lime also precipitates 

 a quantity of impurities. The lime which goes into solution is 

 next precipitated with carbon doxide and the solution is finally 

 neutralized and bleached with sulphur dioxide. 



The sugar solution is next evaporated until the sugar is ready 

 to crystallize. Since inversion would take place at the tempera- 

 ture required for rapid evaporation in the open air, and since 

 there would also be danger of burning, the evaporation is carried 

 on in a vacuum, in which the solution boils at a comparatively 

 low temperature. The solution is drawn off when the sugar is 

 ready to crystallize, allowed to cool, and the mother liquor ex- 

 tracted from the crystals in a centrifuge by centrifugal force. 



Sugar is prepared from sugar cane in essentially the same way. 

 The juice is squeezed out by passing the cane between heavy 

 rollers, instead of being extracted by diffusion. The pressed cane 

 is termed bagasse. The sugar is sent to a refinery for further 

 purification. 



Syrup is prepared from sorghum, sugar cane, or maple sap by 

 evaporating the juice, usually in open kettles, with or without 

 previous purification with lime and sulphur. 



Milk Sugar, C 12 H 2! ,O n , (lactose) is not found in plants, but 

 occurs in the milk of animals to the extent of 3 to 6 per cent. It 

 remains in solution when the casein and fat of milk have been 

 separated (as occurs in the manufacture of cheese), and may be 

 prepared by evaporating the liquid and recrystallization of the 

 product. It appears as hard white crystals with a slightly sweetish 

 taste. It is not as easily soluble in water as cane sugar. It is 

 hydrolyzed to d-galactose and d-glucose. 



