402 SMITH'S INTERMEDIATE CHEMISTRY 



class, the carbohydrates. The word refers to the fact that they 

 contain hydrogen and oxygen in the proportions required to form 

 water, and are, therefore, in a sense, hydrates of carbon. When 

 dehydrating agents like concentrated sulphuric acid (p. 270) 

 act on the carbohydrates, a black mass of carbon is left. 



Sucrose or Cane-Sugar C^E^On. The sugar-cane and the 

 beet produce exceptionally large amounts of this sugar, which is 

 the one commonly used as table sugar. Maple sugar, obtained 

 by evaporating the sap of the tree, is composed mainly of the same 

 substance. 



The sugar-cane forms stalks from ten to twelve feet high. 

 ^hejuices^re_extraced by^crushing the plants betweeiL-rollers. 

 TVip. liquid is evaporated in closed pn,nfi_ A vacuum maintained 

 in the pans permits the boiling of the solution at a low tempera- 

 ture (about 65 degrees) and prevents the decomposition of a part 

 of the sugar which would otherwise occur. When the syrup cools, 

 the sugar crystallizes and the_crystals are freed from the liquid in 

 centrifugal machines. The crystals are brown in color. At the 

 sugar refinery they~are dissolved, and the solutiorus_passed through 

 a column of bone chaxcpal. This adsorbs the coloring matter, 

 and the filtrate is once more evaporated and allowed to crystallize. 

 Refined cane-sugar has a faint yellow tint, and a small amount 

 of ultramarine is added to cover up this tint, and give the 

 white appearance which is popularly connected with purity in 

 sugar. 



The sugar beets, which contain 16 per cent or more of cane- 

 sugar, are slice^ and steepf^ wafpr |n pvtract the su^ar. The 

 liquid con tarns gummy material in colloidal suspension. This is 

 coagulated and precipitated by adding " milk of lime " (calcium 

 hydroxide Ca(OH) 2 suspended in water) and boiling. Carbon 

 dioxide is then passed through the solution to precipitate the 

 excess of lime : 



Ca(OH) ? + C0 2 - CaC0 3 1 + H 2 0. 



