198 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Maltose 

 CH 2 OH GHOH-QH-(CHOH) 2 -CH-O-GH2 CHOH- GH (CHOH) 2 -CHOH 



CH 2 OB-CHOH-CH-(CHOH)7CH-0-CH^ CHOH-CH (CHOH) 2 'CHOH 



or 



.^-0^^ CH 2 OH Q ^ 



CH 2 OH CHOH CH (GHOH) 2 CH-0 CH CH (CHDH) 2 CHOH 

 galactose residue glucose residue 



The large number of possible disaccharides may be partly due to 

 the possibility of combination with the several hydroxyl groups and 

 partly to the possibility of the combination of a- or ft- forms of the 

 constituents, thus 



a a, ft a, 

 -A /8-/8. 



CANE SUGAR. 



Cane sugar is very widely distributed in the vegetable kingdom : 20 per 

 cent, is present in the juice of the sugar cane, 10-20 per cent, in beetroot; 

 smaller quantities are present in the maple and birch and sweet fruits contain 

 cane sugar together with glucose and fructose, which are probably derived 

 from it by hydrolysis; 5-12 percent, of cane sugar is present in bananas, 

 apricots, strawberries and pineapple. The mixture of glucose and fructose in 

 honey is probably the result of the hydrolysis of cane sugar of the flowers by 

 the formic acid secreted by the bees. 



Preparation. 



Cane sugar is prepared mainly from the cane and beet, though other 

 plants, e.g. maple, palm, are used as sources of cane sugar. The manufacture 

 in all cases is very similar. The juice of the cane, prepared by crushing the 

 cane and pressing out, or the aqueous extract of beet, prepared by diffusion 

 in a series of vessels, is treated with milk of lime to neutralise acids and boiled 

 to precipitate proteins. The solution is treated with carbon dioxide to remove 

 the last traces of calcium and with sulphur dioxide to decolorise it. It is 

 again boiled and filtered and evaporated in vacuo until it crystallises. The 

 residue, termed molasses, which does not readily crystallise yields more cane 

 sugar on treatment of the boiling solution with lime or strontia, by which 

 means an insoluble calcium or strontium saccharate is formed. The solid is 

 separated and decomposed with carbon dioxide and the solution yields cane 

 sugar on evaporation. Cane sugar molasses are most frequently fermented 

 and converted into rum. 



Properties. 



Cane sugar in contrast to other sugars crystallises extremely readily and 

 forms colourless monoclinic crystals easily soluble in water and only slightly 

 soluble in alcohol. A saturated solution contains 66 per cent, of cane sugar. 

 It melts on heating to about 160 to a glassy mass termed barley sugar which 

 gradually crystallises again. If it be further heated to about 200 it is changed 

 into a brown substance, caramel, which does not crystallise. 



