THE STORY OF NINETEENTH-CENTURY SCIENCE 



ing of its chemical efficiency, yet from another point of 

 view the " saturated " molecule that is, the molecule 

 whose atoms have their valency all satisfied may be 

 thought of as a relatively fixed or stable organism. 

 Even though it may presently be torn down, it is for 

 the time being a completed structure ; and a considera- 

 tion of the valency of its atoms gives the best clew that 

 has hitherto been obtainable as to the character of its 

 architecture. How important this matter of architecture 

 of the molecule of space relations of the atoms may 

 be was demonstrated as long ago as 1823, when Liebigand 

 Wohler proved, to the utter bewilderment of the chem- 

 ical world, that two substances may have precisely the 

 same chemical constitution the same number and kind 

 of atoms and yet differ utterly in physical properties. 

 The word isomerism was coined by Berzelius to express 

 this anomalous condition of things, which seemed to 

 negative the most fundamental truths of chemistry. 

 Naming the condition by no means explained it, but 

 the fact was made clear that something besides the 

 mere number and kind of atoms is important in the 

 architecture of a molecule. It became certain that 

 atoms are not thrown together haphazard to build a 

 molecule, any more than bricks are thrown together 

 at random to form a house. 



How delicate may be the gradations of architectural 

 design in building a molecule was well illustrated about 

 1850, when Pasteur discovered that some carbon com- 

 pounds as certain sugars can only be distinguished 

 from one another, when in solution, by the fact of their 

 twisting or polarizing a ray of light to the left or to 

 the right, respectively. But no inkling of an explana- 

 tion of these strange variations of molecular structure 



274 



