PROBLEMS OF MODERN SCIENCE 



researches that definite groups of atoms in a 

 molecule may be replaced by other groups of 

 atoms or even by a single atom. It was evident 

 that those atoms which are removed together from 

 a molecule, or persist in union throughout a series 

 of chemical changes, are in some way intimately 

 connected together. By an exhaustive application 

 of this kind of process to a molecule, various 

 clusters of the component atoms can be detected ; 

 and then, the molecule having been thus resolved 

 into simpler components, the fragments may be 

 imagined to be pieced together and a picture of 

 the complete molecular architecture so obtained. 

 The case of acetic acid may be quoted as an illus- 

 tration. The molecule of this substance contains 

 two atoms of carbon, four of hydrogen, and two of 

 oxygen. These facts may be summarised by the 

 formula C 2 H 4 O 2 , where the letters C, H, and O 

 represent carbon, hydrogen, and oxygen, and the 

 numerals the number of each kind of atom present. 

 Numerous chemical reactions of acetic acid show 

 the presence of the following groups of atoms : 

 (OH), (CH 3 ), (CH 3 CO), and (CO,) ; hence, 

 putting these fragments together, the molecular 

 structure of acetic acid appears to be CH 3 COOH. 



The enormous volume of research which has 

 been carried out on these lines has involved the 

 production of many new molecules which have 

 resulted from the breaking up of more complex 

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