CHEMISTRY SINCE TIME OF DALTON 



the trio, linked in this close bond, have no tendency to 

 reach out for any other companion, nor, indeed, any 

 power to hold another should it thrust itself upon them. 

 They form a " stable " compound, which under all ordi- 

 nary circumstances will retain its identity as a molecule 

 of water, even though the physical mass of which it is 

 a part changes its condition from a solid to a gas 

 from ice to vapor. 



But a consideration of this condition of stable equi- 

 librium in the molecule at once suggests a new question : 

 How can an aggregation of atoms, having all their 

 affinities satisfied, take any further part in chemical 

 reactions? Seemingly such a molecule, whatever its 

 physical properties, must be chemically inert, incapable 

 of any atomic readjustments. And so in point of fact 

 it is, so long as its component atoms cling to one an- 

 other unremittingly. But this, it appears, is precisely 

 what the atoms are little prone to do. It seems that 

 they are fickle to the last degree in their individual at- 

 tachments, and are as prone to break away from bond- 

 age as they are to enter into it. Thus the oxygen atom 

 which has just flung itself into the circuit of two hydro- 

 gen atoms, the next moment flings itself free again and 

 seeks new companions. It is for all the world like the 

 incessant change of partners in a rollicking dance. 



This incessant dissolution and reformation of mole- 

 cules in a substance which as a whole remains apparrnt- 

 ly unchanged was first fully appreciated by Ste. -Claire 

 Deville, and by him named dissociation. It is a proc- 

 ess which goes on much more actively in some com- 

 pounds than in others, and very much more actively 

 under some physical conditions (such as increase of 



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