416 CHEMICAL DISCOVERY AND INVENTION 



in any approach to completeness before the general reader. It 

 will be sufficient if we endeavour to trace the transformations of 

 a few of the more important members of the group, and if 

 possible give some idea of the views entertained by modern 

 chemists as to their constitution. 



The origin of cane sugar has been already sufficiently described. 

 Another sugar which has the same composition but very different 

 properties is contained in milk to the extent of nearly 5 per cent. 

 Milk sugar or lactose is obtained by evaporating clear whey to a 

 syrup, when on standing the sugar crystallises in hard crusts 

 and crystals which contain C^H^O^ united with one molecule 

 of water of crystallisation. 



Maltose is another sugar having the same formula which is 

 produced by the action of malt extract, containing diastase, on 

 starch, and hence is formed in the preliminary stages of the 

 fermentation of beer or grain spirit. Both these substances are 

 less sweet than common sugar, but all three agree in undergoing 

 a change under the influence of a small quantity of an acid 

 which results in each breaking up into two sugars of a simpler 

 type, the molecule of which contains only six atoms of carbon, 

 and which are called glucoses or saccharoses. 



Disaccharose. Saccharoses. 



Cane sugar Glucose Fructose 1 



C 12 H 22 11 +H 2 0=C 6 H 12 6 +C 6 H 12 6 



Milk sugar Glucose Galactose 



Maltose Glucose 



C 12 H 22 11 +H 2 0=2C 6 H 12 6 



Glucose or grape sugar occurs in ripe grapes and raisins, and is 

 manufactured by heating starch with water till liquefied, and 

 boiling the solution with a small quantity of sulphuric acid. 

 After complete conversion of the starch the liquid is neutralised 

 by adding a slight excess of chalk, filtering, and after passing 

 through charcoal, evaporating the solution to crystallising con- 

 sistency. Glucose is manufactured for use in preserving fruit 

 and jam, and in the production of beer and so-called " malt " 

 vinegar. 



Fructose or fruit sugar is associated with glucose in many 

 fruits. Like glucose it ferments in the presence of yeast and 

 1 This change occurs when sugar is cooked with sour fruit. 



