THE CHEMISTRY OF THE SUGARS 83 



and comprises a large number of substances which are classified 

 as carbohydrates. A carbohydrate is a compound of carbon 

 with hydrogen and oxygen, the last two elements being in 

 the proportion to form water ; the simplest carbohydrate, 

 therefore, would be CH 2 0. As a matter of fact this is 



H 



formaldehyde with the constitutional formula | /H. 



<0 



There is considerable evidence for believing that the great 

 family of carbohydrates as found in nature may originate 

 in the first instance from formaldehyde. A suggestion of this 

 sort appears reasonable even when we simply look at the 

 empirical formulae of the three great classes of carbohydrates 

 generally termed the mono-saccharoses, the di-saccharoses, 

 and the poly-saccharoses. These terms are not altogether 

 satisfactory, because the so-called mono-saccharoses include a 

 large number of substances of differing molecular weight and 

 molecular formulae, all of which have the general formula 

 C n H 2n O n ; the best known members of this group are, however, 

 the hexoses of the general formula C 6 H 12 6 , and the di- 

 saccharoses are so named because by addition of a molecule of 

 water they give rise to two molecules of a hexose. The general 

 formula, therefore, of the di-saccharoses is C 12 H2 2 U . The 

 poly-saccharoses are much more complicated substances whose 

 molecular formulae are unknown, but they have the general 

 formula (C 6 H 10 5 ) n . 



Taking now, for the sake of comparison, an even number 

 of carbon atoms in all three cases we get the following relation- 

 ship : 



mono-saccharoses (two or more molecules) C^H^O^ 

 di-saccharoses Ci2H 22 O n 



poly-saccharoses (n = 2) C 12 H 20 10 



We can thus see at a glance how these important naturally 



02 



