THE STORY OF NINETEENTH-CENTURY SCIENCE 



its former prestige as the all-important personage of the 

 chemical world. Since so much depends upon the mere 

 position of the atoms, it may appear that comparatively 

 little depends upon the nature of the atoms themselves. 

 But such a view is incorrect, for on closer consideration 

 it will appear that at no time has the atom been seen to 

 renounce its peculiar personality. Within certain limits 

 the character of a molecule may be altered by changing 

 the positions of its atoms (just as different buildings may 

 be constructed of the same bricks), but these limits are 

 sharply defined, and it would be as impossible to exceed 

 them as it would be to build a stone building with bricks. 

 From first to last the brick remains a brick, whatever 

 the style of architecture it helps to construct; it never 

 becomes a stone. And just as closely does each atom 

 retain its own peculiar properties, regardless of its sur- 

 roundings. 



Thus, for example, the carbon atom may take part in 

 the formation at one time of a diamond, again of a piece 

 of coal, and yet again of a particle of sugar, of wood 

 fibre, of animal tissue, or of a gas in the atmosphere; 

 but from first to last from glass-cutting gem to in- 

 tangible gas there is no demonstrable change whatever 

 in any single property of the atom itself. So far as we 

 know, its size, its weight, its capacity for vibration or 

 rotation, and its inherent affinities, remain absolutely 

 unchanged throughout all these varying fortunes of po- 

 sition and association. And the same thing is true of 

 every atom of all of the sixty-odd elementary substances 

 with which the modern chemist is acquainted. Every 

 one appears always to maintain its unique integrity, 

 gaining nothing and losing nothing. 



All this being true, it would seem as if the position of 



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