54 THE THEORY OF IONS 



to the dyad or bipolar oxygen, while one pole is 

 occupied by the H atom, and the fourth valency 

 remains free and demands satisfaction. CHO is 

 therefore a monad or monovalent ion. Where this 

 is satisfied by an H ion directly, or indirectly through 

 displacement of the by an OH ion, we have the 

 molecule CH 2 0, which is methyl aldehyde. This has 

 a strong tendency to polymerise ; in fact, poly- 

 merisation is a great characteristic of the aldehydes 

 as a group. Thus when two molecules are linked 

 together they form glycollic aldehyde, C 2 H 4 2 ; 

 when three molecules are linked together they form 

 Trioses, C 3 H 6 3 , e.g. glycerose ; four molecules form 

 Tetroses, C 4 H 8 O 4 , e.g. erythose ; five molecules form 

 Pentoses, C 5 H 10 5 , e.g. arabinose or xylose ; and by 

 linking together six molecules we have formed the 

 Hexoses or Glucoses, C 6 H 12 6 , including dextrose, 

 laevulose, galactose, mannose, acrose, etc. Singly 

 linked compounds of carbon containing hydroxyls, 

 besides the aldehyde nucleus, are termed Aldols 

 (contracted from alcoholic aldehyde), and when each 

 carbon atom except the aldehyde nucleus is linked 

 with one hydroxyl (OH) it is called a carbohydrate* 

 Thus : 



6 

 Dextrose, C G H 12 6 



Holler's " Chemistry/' p. 155. 



