THE CHEMISTRY OP 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 CH2O. As a matter of fact this is 



H 



formaldehyde with the constitutional formula | .H. 



C< 

 



There is considerable evidence for beUeving 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, aU of which have the general formula 

 C„H2„0„ ; the best known members of this group are, however, 

 the hexoses of the general formula CgHisOe, 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 Ci2H220xi. The 

 poly-saccharoses are much more complicated substances whose 

 molecular formulae are unknown, but they have the general 

 formula (CeHioOs)^. 



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) C12H24O1J 

 di-saccharoses C12H22O11 



poly-saccharoses {n = 2) C12H20O10 



We can thus see at a glance how these important naturally 



o 2 



