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PRINCIPLES OF AGRICULTURAL, CHEMISTRY 



which is prepared from sugar cane or sugar beets, is the most 

 common sugar. Sugars are divided into two groups : the simple 

 sugars, or monosaccharides, represented by glucose, and the com- 

 plex sugars, or polysaccharides, represented by cane sugar or suc- 

 rose. The complex sugars can be split up into one or more kinds 

 of simple sugars. The sugars can all be crystallized, but in some 

 cases crystallization is difficult. 



Fig. 80. A polariscope. 



Sugars are acted upon by acids and alkalies, forming various 

 products, some of which are brown in color. Boiled with con- 

 centrated hydrochloric acid, cane sugar gives a black precipitate 

 called humic acid, the name being given chiefly on account of its 

 black color. 



Optical Properties of Sugars. If a ray of light is passed 

 through a crystal of Iceland spar, it is split up into two rays, 

 having peculiar properties, and called polarized light. If a ray 

 of this polarized light falls upon another parallel crystal, in one 

 position no light will pass through ; if the crystal is rotated at an 

 angle of 45, all the light goes through, while in intermediate posi- 

 tions only a part is transmitted. 



If the two crystals referred to above are placed so that all the 

 light passes through, and a solution of sugar then placed between 

 them, the polarized light will no longer all go through the second 

 prism, but the prism must be rotated to a certain angle before the 

 light will all pass through. The sugar has twisted the ray of 



