650 



TRANS. ST. I.OUIS ACAD. SCIENCE. 



the ions is used in overcoming and virtually reducino^ to zero the 

 polarities which held them together. This work is equivalent to 

 the energy evolved when the ions reassume their polarities, i.e., 

 when they reunite. 



Two atoms united into a molecule may be compared to two 

 permanent magnets united by their opposite poles and forming 

 a molecule which would present no external polarity. If, now, 

 these magnets be separated by removing one to an infinite dis- 

 tance, their polarities (toward each other, not their internal polar- 

 ities) are reduced to zero ; and the energy expended in removing 

 the magnet reappears when they reassume their polarities, i.e., 

 when they unite again. 



The valence or capacity of an atom for electro -polarity may 

 vary greatly, depending upon the intensity of the force tending to 

 polarize it, that is, upon the valence of the ion with which it com- 

 bines. The valence of many atoms, however, such as O, seems 

 to be constant. The maximum and minimum valences of an atom 

 represent the limits of its capacity for polarization, or its satura- 

 tion points. 



This conception may be more easily understood by reference to 

 the illustration previously cited. 



Let M and M', Fig. i, be two permanent magnets bent in the 

 form of rings with their poles close together at NS and N^S' re- 

 spectively. Suppose the permanent magnetism is due not to any 

 peculiar quality of the material, but to a perpetual electrical vor- 

 tex-ring coinciding with the magnet. 



Around each magnet is wound a coil of insulated wire, through 

 which a current may be passed at will. 



Suppose the poles of the magnet, M, are in actual contact. The 

 magnet is then a closed ring and has no polarity. Suppose two 

 such magnets are made to approach each other, and that this op- 

 eration is equivalent to separating their poles. The two magnets 

 now unite by their opposite poles as shown in Fig. 2, forming a 

 molecule which is itself a closed magnetic ring having no exter- 

 nal polarity. If the polarizing capacity (valence) of M is n times 

 that of M', it will require n of the latter to neutralize one of the 

 former and produce a saturated molecule. 



Suppose a current is passed through the coils so as to oppose 

 the magnetism of the rings. If the magnetic field set up by the 



