PROPERTIES OF AQUEOUS SALT SOLUTIONS 323 



bivalent metals one of 30 per cent, and although the un-ionized 

 molecules present contain in some cases the elements hydrogen, lith- 

 ium, and beryllium of very small atomic weights, and in two others 

 the elements thallium and barium of large atomic weights. 



If there were not other evidence to the contrary, the existence of 

 this general principle, which is also applicable to many other proper- 

 ties, would almost warrant the conclusion that the salts are completely 

 ionized up to the concentration in question, and that the decrease in 

 conductivity is due merely to a change in migration-velocity. But, 

 in view of the apparently conclusive evidence against such an hypo- 

 thesis, we can only conclude that the form of union represented by the 

 un-ionized molecules of salts differs essentially from ordinary chemical 

 combination, it being so much less intimate that the ions still exhibit 

 their characteristic properties, in so far as these are not dependent 

 upon their existence as separate aggregates. 



These, then, are the empirical principles to which a critical analysis 

 of the experimental data leads. Upon these principles must be based 

 the rational, theoretical explanation of the phenomena in question. 

 The discovery of that explanation constitutes one of the most import- 

 ant of the present problems of physical chemistry. 



