THE CENTURY'S PROGRESS IN CHEMISTRY 



Ho\v 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 another 

 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 attachments, 

 and are as prone to break away from bondage as they are 

 to enter into it. Thus the oxygen atom which has just 

 flung itself into the circuit of two hydrogen atoms, the 

 next moment flings itself free again and seeks new com- 

 panions. It is for all the world like the incessant change 

 of partners in a rollicking dance. 



This incessant dissolution and reformation of molecules 

 in a substance which as a whole remains apparently un- 

 changed was first fully appreciated by Ste.-Claire Deville, 

 and by him named dissociation. It is a process which 

 goes on much more activety in some compounds than in 

 others, and very much more actively under some physi- 

 cal conditions (such as increase of temperature) than un- 

 der others. But apparently no substances at ordinary 

 temperatures, and no temperature above the absolute 

 zero, are absolutely free from its disturbing influence. 

 Hence it is that molecules having all the valency of 

 their atoms fullv satisfied do not lose their chemical 

 activity since each atom is momentarily free in the 

 exchange of partners, and may seize upon different 

 atoms from its former partners, if those it prefers are 

 at hand. 



While, however, an appreciation of this ceaseless 

 activity of the atom is essential to a proper understand- 

 s 273 



